# EDGAR Filing Document

**Accession Number:** 0001722964
**File Stem:** 0001104659-25-074284
**Filing Date:** 2025-8
**Character Count:** 69981
**Document Hash:** 527ecdbeaa46d073c44404a1eee0da1d
**Contains OCR:** False
**Source Format:** 

## Filing Content

## Filing Summary
**0001104659-25-074284.hdr.sgml**: 20250805

**ACCESSION NUMBER**: 0001104659-25-074284

**CONFORMED SUBMISSION TYPE**: SC14D9C

**PUBLIC DOCUMENT COUNT**: 8

**FILED AS OF DATE**: 20250805

**DATE AS OF CHANGE**: 20250805

**SUBJECT COMPANY**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** Y-mAbs Therapeutics, Inc.
- **CENTRAL INDEX KEY:** 0001722964
- **STANDARD INDUSTRIAL CLASSIFICATION:** PHARMACEUTICAL PREPARATIONS [2834]
- **ORGANIZATION NAME:** 03 Life Sciences
- **EIN:** 474619612
- **STATE OF INCORPORATION:** DE
- **FISCAL YEAR END:** 1231

**FILING VALUES:**
- **FORM TYPE:** SC14D9C
- **SEC ACT:** 1934 Act
- **SEC FILE NUMBER:** 005-90649
- **FILM NUMBER:** 251186126

**BUSINESS ADDRESS:**
- **STREET 1:** 202 CARNEGIE CENTER
- **STREET 2:** SUITE 301
- **CITY:** PRINCETON
- **STATE:** NJ
- **ZIP:** 08540
- **BUSINESS PHONE:** 646-885-8505

**MAIL ADDRESS:**
- **STREET 1:** 202 CARNEGIE CENTER
- **STREET 2:** SUITE 301
- **CITY:** PRINCETON
- **STATE:** NJ
- **ZIP:** 08540
**FILED BY**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** Y-mAbs Therapeutics, Inc.
- **CENTRAL INDEX KEY:** 0001722964
- **STANDARD INDUSTRIAL CLASSIFICATION:** PHARMACEUTICAL PREPARATIONS [2834]
- **ORGANIZATION NAME:** 03 Life Sciences
- **EIN:** 474619612
- **STATE OF INCORPORATION:** DE
- **FISCAL YEAR END:** 1231

**FILING VALUES:**
- **FORM TYPE:** SC14D9C

**BUSINESS ADDRESS:**
- **STREET 1:** 202 CARNEGIE CENTER
- **STREET 2:** SUITE 301
- **CITY:** PRINCETON
- **STATE:** NJ
- **ZIP:** 08540
- **BUSINESS PHONE:** 646-885-8505

**MAIL ADDRESS:**
- **STREET 1:** 202 CARNEGIE CENTER
- **STREET 2:** SUITE 301
- **CITY:** PRINCETON
- **STATE:** NJ
- **ZIP:** 08540

**UNITED STATES**

**SECURITIES AND EXCHANGE COMMISSION**

**Washington, D.C. 20549**

**SCHEDULE 14D-9**

**Solicitation/Recommendation Statement**

**Under Section 14(d)(4) of the Securities Exchange Act of 1934**

**Y-MABS THERAPEUTICS, INC.** 

(Name of Subject Company)

**Y-MABS THERAPEUTICS, INC.** 

(Name of Persons Filing Statement)

**Common Stock, $0.0001 par value per share**

(Title of Class of Securities)

**984241109** 

(CUSIP Number of Class of Securities)

**Michael Rossi**

**President and Chief Executive Officer**

**Y-mAbs Therapeutics, Inc.**

**202 Carnegie Center Drive**

**Suite 301**

**Princeton, New Jersey 08540**

**(646) 885-8505**

(Name, address, and telephone number of person authorized to receive notices and communications

on behalf of the persons filing statement)

***With a copy to:***

**Divakar Gupta** 

**Sarah K. Sellers**

**Bill Sorabella**

**Bill Roegge**

**Cooley LLP** 

**55 Hudson Yards** 

**New York, New York 10001** 

**(212) 479-6000** 

&nbsp;&nbsp;&nbsp;&nbsp;⌧ Check the box if the filing relates solely to preliminary communications
made before the commencement of a tender offer.

This Schedule 14D-9 filing consists of certain communications relating to the proposed acquisition of Y-mAbs Therapeutics, Inc., a Delaware corporation (the "Company" or "Y-mAbs"), by Perseus BidCo US, Inc., a Delaware corporation ("Parent"), and Yosemite Merger Sub, Inc., a Delaware corporation and a wholly owned subsidiary of Parent ("Purchaser"), pursuant to the terms and subject to the conditions of an Agreement and Plan of Merger, dated as of August 4, 2025 (the "Merger Agreement"), by and among the Company, Parent, Purchaser, and Stark International Lux, a Luxembourg private limited liability company (*société à responsabilité limitée*). Pursuant to the Merger Agreement, upon the terms and subject to the conditions thereof, Purchaser will commence a tender offer (the "Tender Offer") to acquire all of the outstanding shares of common stock of the Company, $0.0001 par value per share (the "Shares"), at an offer price of $8.60 per Share in cash, without interest, and subject to any applicable withholding taxes. If successful, the Tender Offer will be followed by a merger of Purchaser with and into the Company (the "Merger") pursuant to Section 251(h) of the Delaware General Corporation Law, with the Company continuing as the surviving corporation in the Merger.

This Schedule 14D-9 filing consists of the following communications relating to the proposed Tender Offer and the Merger:

&nbsp;&nbsp;&nbsp;&nbsp;· [Exhibit 99.1: Joint Press Release issued by Parent and the Company, dated August 5, 2025 (incorporated by reference to Exhibit 99.1 of the Current Report on Form 8-K filed by the Company with the U.S. Securities and Exchange Commission on August 5, 2025).](tm2522599d1_ex99-1.htm)

&nbsp;&nbsp;&nbsp;&nbsp;· [Exhibit 99.2: Email from Michael Rossi, President and Chief Executive Officer of the Company, sent to employees, dated August 5, 2025.](tm2522599d1_ex99-2.htm)

&nbsp;&nbsp;&nbsp;&nbsp;· [Exhibit 99.3: Investor/Analyst Letter, dated August 5, 2025.](tm2522599d1_ex99-3.htm)

&nbsp;&nbsp;&nbsp;&nbsp;· [Exhibit 99.4: Patient and Patient Advocacy Organization Letter, dated August 5, 2025.](tm2522599d1_ex99-4.htm)

&nbsp;&nbsp;&nbsp;&nbsp;· [Exhibit 99.5: Vendor/Supplier Letter, dated August 5, 2025.](tm2522599d1_ex99-5.htm)

&nbsp;&nbsp;&nbsp;&nbsp;· [Exhibit 99.6: LinkedIn Post, dated August 5, 2025.](tm2522599d1_ex99-6.htm)

## Exhibit 99.1

**Exhibit 99.1**

**FOR IMMEDIATE RELEASE** 

**SERB Pharmaceuticals Agrees to Acquire Y-mAbs Therapeutics**

*Acquisition to Include DANYELZA<sup>®</sup>(Naxitamab-gqgk), Further Broadening SERB's Rare Oncology Product Portfolio*

 

*Transaction Expands SERB's Investment in the U.S.*

*SERB to Commence All-Cash Tender Offer to Acquire All Outstanding Shares of Y-mAbs for $8.60 Per Share* 

 

*Represents 105% Premium to Y-mAbs Closing Share Price on August 4, 2025*

 

**WEST CONSHOHOCKEN, PA and PRINCETON, NJ, August 5, 2025** – SERB Pharmaceuticals ("SERB"), a global specialty pharmaceutical company focused on medicines for rare diseases and medical emergencies, and Y-mAbs Therapeutics, Inc. (Nasdaq: YMAB) ("Y-mAbs" or "the Company"), a commercial-stage biopharmaceutical company focused on the development and commercialization of antibody-based therapeutics for the treatment of cancer, today announced that they have entered into a definitive merger agreement under which SERB will acquire Y-mAbs, including its lead commercial oncology asset, DANYELZA<sup>®</sup> (naxitamab-gqgk), in an all-cash transaction, representing an equity value for Y-mAbs of approximately $412 million.

 

Under the terms of the merger agreement, SERB will commence an all-cash tender offer to purchase all outstanding shares of Y-mAbs common stock. Holders of Y-mAbs common stock would receive $8.60 per share in cash, representing a premium of approximately 105% to Y-mAbs' closing share price on August 4, 2025, the last full trading day prior to the transaction announcement.

The transaction was unanimously approved by the Y-mAbs Board of Directors following a review of strategic alternatives to maximize value for Y-mAbs stockholders, with the assistance of external advisors. The process included discussions with numerous potential buyers for Y-mAbs or for the DANYELZA or Radiopharmaceuticals businesses on a standalone basis. In addition, the Board reviewed potential sources of additional capital to support accelerating the further development of the Company's pipeline.

With a focus on pediatric oncology, Y-mAbs successfully developed and commercialized the anti-GD2 therapy, DANYELZA (naxitamab-gqgk). DANYELZA is the first FDA-approved treatment for relapsed or refractory high-risk neuroblastoma – a rare and aggressive pediatric cancer – and was approved in the United States under accelerated approval based on overall response rate and duration of response. DANYELZA is indicated for the treatment of pediatric patients one year of age and older and adult patients with relapsed or refractory high-risk neuroblastoma in the bone or bone marrow who have demonstrated a partial response, minor response, or stable disease to prior therapy. In addition to inpatient use, doctors can choose to administer DANYELZA in an outpatient setting, which may reduce the logistical burden on patients and their families. Y-mAbs' portfolio also includes an investigational therapy targeting GD2 in solid tumors and CD38 in circulating tumors in ongoing Phase 1 clinical trial from its Self-Assembly DisAssembly ("SADA") Pretargeted Radioimmunotherapy Platform ("PRIT").

Vanessa Wolfeler, Chief Executive Officer of SERB: "High-risk neuroblastoma is not only a rare and devastating pediatric cancer but also one of the most difficult to treat. DANYELZA is recognized as a critical treatment option for patients and expands the treatment pathways available to providers in an outpatient setting. Working together with the team from Y-mAbs, I believe we can continue generating data for this product, expand partnerships to additional oncology centers, and have a positive impact on the lives of more neuroblastoma patients and their families."

Jeremie Urbain, Chairman of SERB: "Following SERB's expansion into the United States five years ago, this acquisition reflects another milestone in the execution of our growth strategy to build a leading global specialty pharma platform. DANYELZA is an excellent strategic fit for SERB as it strengthens our existing rare oncology portfolio and will allow us to leverage our existing global footprint and our medical, regulatory, and commercial expertise to expand the reach of DANYELZA to new markets."

SERB has a growing portfolio of medicines for rare emergency medicine, rare diseases, and CBRN preparedness, supplying healthcare providers around the world. The acquisition of DANYELZA broadens SERB's existing Rare Oncology portfolio (Voraxaze<sup>®</sup>, Vistogard<sup>®</sup>, Xermelo<sup>®</sup>) and furthers its mission of building a leading portfolio of medicines that improve the standard of care for patients globally.

Michael Rossi, President, Chief Executive Officer and a member of the Board of Directors, Y-mAbs: "Our Board regularly reviews our business, including our strategy, the current state of the biopharmaceutical sector and the time and resources required to execute on our strategic plans. Following the thorough process to explore all of the potential paths forward for the Company, we are now moving forward with this agreement with SERB that we believe reflects the most attractive option available to Y-mAbs, providing significant, immediate and certain value to our stockholders."

Mr. Rossi continued: "This transaction is a testament to our team's hard work in building a strong foundation as a commercial organization with a differentiated, FDA-approved product in DANYELZA. We believe that Y-mAbs has made important progress advancing DANYELZA and our Radiopharmaceuticals platform. By combining our expertise and resources with SERB's specialty commercial capabilities, we can extend our shared commitment of improving the lives of even more patients and families on a global scale."

**Transaction Details**

Under the terms of the merger agreement, SERB is obligated to commence a tender offer by August 19, 2025, to purchase all of Y-mAbs' outstanding shares for $8.60 per share in cash. Assuming a majority of the outstanding Y-mAbs shares are tendered into, and not withdrawn from, the tender offer, and subject to the satisfaction of other customary conditions, including the receipt of a majority of Y-mAbs shares in the tender offer and expiration or termination of the applicable waiting period under the Hart-Scott-Rodino Antitrust Improvements Act, SERB is required to close the tender offer, following which, Y-mAbs will be merged with a subsidiary of SERB. After such merger, Y-mAbs shares that were not tendered in the tender offer will be converted into the right to receive the same $8.60 per share in cash paid for shares in the tender offer, and Y-mAbs' stock will no longer be listed on the Nasdaq exchange.

Y-mAbs stockholders holding approximately 16% of Y-mAbs' outstanding shares of common stock have entered into a tender and support agreement with SERB, pursuant to which such stockholders have agreed, among other things, to tender all of their shares of Y-mAbs common stock in the tender offer, subject to the terms and conditions of such agreement.

The transaction is expected to close by the fourth quarter of 2025.

**Advisors**

Rothschild & Co. is acting as exclusive financial advisor, Freshfields US LLP is acting as legal counsel and H/Advisors Abernathy is acting as strategic communications advisor to SERB.

Centerview Partners is acting as exclusive financial advisor, Cooley LLP is acting as legal counsel and Joele Frank, Wilkinson Brimmer Katcher is acting as strategic communications advisor to Y-mAbs.

**About SERB Pharmaceuticals**

SERB is a global specialty pharmaceutical company with a growing portfolio of medicines for rare emergency medicine, rare diseases, and CBRN preparedness. For over 30 years we have made treating complex and life-threatening conditions possible, supporting clinicians, healthcare systems and governments while offering hope to patients and their families. The company's Rare Oncology portfolio includes Voraxaze<sup>®</sup> (glucarpidase), Vistogard<sup>®</sup> (uridine triacetate), Xermelo<sup>®</sup> (telotristat ethyl). SERB is also a leading provider of essential acute care medicines, addressing unmet medical needs and supplying antidotes and medical countermeasures for chemical, biological, radiological and nuclear (CBRN) risks. As a fully integrated company, we have the experience and capabilities to acquire, develop, and manufacture our medicines to the highest standards, and make them available worldwide through our secure supply chain.**** 

<br> Learn more at https://SERB.com

**About Y-mAbs**

Y-mAbs is a commercial-stage biopharmaceutical company focused on the development and commercialization of novel, radioimmunotherapy and antibody-based therapeutic cancer products. The Company's broad and advanced commercial product pipeline includes the anti-GD2 therapy DANYELZA<sup>®</sup> (naxitamab-gqgk), the first FDA-approved treatment for patients with relapsed or refractory high-risk neuroblastoma in the bone or bone marrow after a partial response, minor response, or stable disease to prior therapy. The Company's technologies include its investigational Self-Assembly DisAssembly ("SADA") Pretargeted Radioimmunotherapy Platform ("PRIT") and bispecific antibodies generated using the Y-BiClone platform.

**About DANYELZA<sup>®</sup> (naxitamab-gqgk)**

DANYELZA<sup>®</sup> (naxitamab-gqgk) is indicated, in combination with granulocyte-macrophage colony-stimulating factor ("GM-CSF"), for the treatment of pediatric patients one year of age and older and adult patients with relapsed or refractory high-risk neuroblastoma in the bone or bone marrow who have demonstrated a partial response, minor response, or stable disease to prior therapy. This indication was approved under accelerated approval based on overall response rate and duration of response. Continued approval for this indication may be contingent upon verification and description of clinical benefits in a confirmatory trial. DANYELZA<sup>®</sup> includes a Boxed Warning for serious infusion-related reactions, such as cardiac arrest and anaphylaxis, and neurotoxicity, such as severe neuropathic pain and transverse myelitis. See full Prescribing Information for complete Boxed Warning and other important safety information <u>here</u>.

DANYELZA is currently not approved for the treatment of osteosarcoma in any jurisdiction.

**Forward-Looking Statements**

This press release contains forward-looking statements that involve risks and uncertainties relating to future events and the future performance of Y-mAbs and Serb, including statements relating to the ability to complete and the timing of completion of the transactions contemplated by the Agreement and Plan of Merger dated as of August 4, 2025 by and among Y-mAbs, Serb, and the other parties thereto (the "Merger Agreement"), including the anticipated occurrence, manner and timing of the proposed tender offer, the parties' ability to satisfy the conditions to the consummation of the tender offer and the other conditions to the consummation of the subsequent merger set forth in the Merger Agreement, the possibility of any termination of the Merger Agreement, and the prospective benefits of the proposed transaction, including with respect to the potential for additional data for DANYELZA, the potential expansion of partnerships to additional oncology centers, the ability to have a positive impact on the lives of more neuroblastoma patients and their families and Serb's ability to leverage its existing global footprint and its medical, regulatory, and commercial expertise to expand the reach of DANYELZA to new markets; and other statements that are not historical facts. The forward-looking statements contained in this release are based on current expectations and assumptions that are subject to risks and uncertainties which may cause actual results to differ materially from the forward-looking statements. These statements may contain words such as "may," "will," "would," "could," "expect," "anticipate," "intend," "plan," "believe," "estimate," "project," "seek," "should," "strategy," "future," "opportunity," "potential" or other similar words and expressions indicating future results. Risks that may cause these forward-looking statements to be inaccurate include, without limitation: uncertainties as to the timing of the tender offer; uncertainties as to how many of Y-mAbs' stockholders will tender their stock in the offer; the possibility that competing offers or acquisition proposals will be made; the possibility that various closing conditions for the transaction may not be satisfied or waived, including that a governmental entity may prohibit, delay, or refuse to grant approval for the consummation of the transaction (or only grant approval subject to adverse conditions or limitations); the difficulty of predicting the timing or outcome of regulatory approvals or actions, if any; the occurrence of any event, change or other circumstance that could give rise to the termination of the Merger Agreement; the possibility that the transaction does not close; risks related to the parties' ability to realize the anticipated benefits of the proposed transaction, including the possibility that the expected benefits from the proposed acquisition will not be realized or will not be realized within the expected time period and that Y-mAbs and Serb will not be integrated successfully or that such integration may be more difficult, time-consuming or costly than expected; the effects of the transaction on relationships with employees, customers, suppliers, other business partners or governmental entities; negative effects of this announcement or the consummation of the proposed transaction on the market price of Y-mAbs' common stock and/or Y-mAbs' operating results; significant transaction costs; unknown or inestimable liabilities; the risk of litigation and/or regulatory actions related to the proposed transaction; SERB's ability to fund the proposed transaction; obtaining and maintaining adequate coverage and reimbursement for products; the time-consuming and uncertain regulatory approval process; the costly and time-consuming pharmaceutical product development process and the uncertainty of clinical success, including risks related to failure or delays in successfully initiating or completing clinical trials and assessing patients; global economic, financial, and healthcare system disruptions and the current and potential future negative impacts to the parties' business operations and financial results; the sufficiency of the parties' cash flows and capital resources; the parties' ability to achieve targeted or expected future financial performance and results and the uncertainty of future tax, accounting and other provisions and estimates; and other risks and uncertainties affecting Y-mAbs and Serb, including those described from time to time under the caption "Risk Factors" and elsewhere in Y-mAbs' filings and reports with the U.S. Securities and Exchange Commission (the "SEC"), including Y-mAbs' Annual Report on Form 10-K for the fiscal year ended December 31, 2024 and Quarterly Report on Form 10-Q for the quarterly period ended March 31, 2025, as well as the Tender Offer Statement on Schedule TO and related tender offer documents to be filed by Serb and its acquisition subsidiary, and the Solicitation/Recommendation Statement on Schedule 14D-9 to be filed by Y-mAbs. Any forward-looking statements are made based on the current beliefs and judgments of Y-mAbs' and Serb's management, and the reader is cautioned not to rely on any forward-looking statements made by Y-mAbs or Serb. Except as required by law, Y-mAbs and Serb do not undertake any obligation to update (publicly or otherwise) any forward-looking statement, including without limitation any financial projection or guidance, whether as a result of new information, future events, or otherwise.

**Important Information about the Tender Offer and Where to Find It**

The tender offer (the "Offer") for the Y-mAbs outstanding common stock referred to in this release has not yet commenced. The description contained in this release is neither an offer to purchase nor a solicitation of an offer to sell any securities, nor is it a substitute for the tender offer materials that Serb will file with the SEC. The solicitation and offer to purchase Y-mAbs' common stock will only be made pursuant to an offer to purchase and related tender offer materials. At the time the Offer is commenced, Serb will file a tender offer statement on Schedule TO and thereafter Y-mAbs will file a solicitation/recommendation statement on Schedule 14D-9 with the SEC with respect to the Offer.

THE TENDER OFFER MATERIALS (INCLUDING AN OFFER TO PURCHASE, A RELATED LETTER OF TRANSMITTAL AND CERTAIN OTHER OFFER DOCUMENTS) AND THE SOLICITATION/RECOMMENDATION STATEMENT ON SCHEDULE 14D-9, AS THEY MAY BE AMENDED OR SUPPLEMENTED FROM TIME TO TIME, WILL CONTAIN IMPORTANT INFORMATION. ANY HOLDERS OF Y-mAbs SHARES ARE URGED TO READ THESE DOCUMENTS CAREFULLY WHEN THEY BECOME AVAILABLE BECAUSE THEY WILL CONTAIN IMPORTANT INFORMATION THAT HOLDERS SHOULD CONSIDER BEFORE MAKING ANY DECISION REGARDING TENDERING THEIR SHARES.

The offer to purchase, the letter of transmittal, the solicitation/recommendation statement and related offer documents will be made available for free at the SEC's website at <u>www.sec.gov</u>. Copies of those offer documents and all other documents filed by Serb and Y-mAbs will be made available at no charge by directing a request to the information agent for the Offer, which will be named in the Schedule TO to be filed with the SEC. Copies of the solicitation/recommendation statement on Schedule 14D-9 to be filed with the SEC by Y-mAbs will be available free of charge on Y-mAbs' investor relations website at <u>https://ir.ymabs.com/</u> or by contacting Y-mAbs' investor relations contact at <u>cdu@ymabs.com</u>.

In addition, Y-mAbs files annual, quarterly and current reports and other information with the SEC, which are also made available free of charge on the Company's investor relations website at <u>https://ir.ymabs.com/</u> and at the SEC's website at www.sec.gov.

**CONTACTS**

**SERB Media** 

Chris Sampson,

Director, Corporate Communications and ESG

<u>chris.sampson@serb.com</u>

**Y-mAbs Investors**

Courtney Dugan

VP, Head of Investor Relations

<u>cdu@ymabs.com</u>

**Y-mAbs Media** 

Aaron Palash / Fouad Boutros

Joele Frank, Wilkinson Brimmer Katcher

212-355-4449

## Exhibit 99.2

**Exhibit 99.2**

**Y-mAbs Employee Email**

***Sender***: Mike Rossi

***Subject***: Important Update on the Next Step in Our Y-mAbs Journey

***Send***  ***Date***: August 5, 2025

***Distribution***: All Employees

Y-mAbs Team,

Since day one, our mission at Y-mAbs Therapeutics has been clear: bring important new therapies to patients as quickly as possible. Through DANYELZA®, our company has brought one of the most important innovations in pediatric neuroblastoma to market, helping to improve the lives of countless patients and giving the gifts of childhood and invaluable quality time back to them and their families. At the same time, we have also made progress advancing our Radiopharmaceuticals businesses. Our focus on helping extend and improve patients' lives through innovative therapeutic solutions for life's most threatening diseases has not changed.

Today, we are announcing a transaction that reflects the hard work of our current and past employees who have built a strong foundation as a commercial organization with a differentiated, FDA-approved anti-GD2 therapy.

Specifically, we have entered into an agreement under which SERB Pharmaceuticals has agreed to acquire Y-mAbs for $8.60 per share in an all-cash transaction with an equity value of $412 million. You can view the full press release that we just issued <u>here</u>.

SERB is a global specialty pharmaceutical company with a portfolio of critical medicines that treat complex and life-threatening conditions. By combining our expertise and resources with their specialty commercial capabilities, we can extend our shared commitment of improving the lives of even more patients and families on a global scale.

This transaction is the result of the Board of Directors' review of strategic alternatives to maximize value for Y-mAbs stockholders, with the assistance of external advisors. We are now moving forward with this agreement, which we believe reflects the most attractive option available to Y-mAbs and provides significant, immediate and certain value to our stockholders. At the same time, we believe that the transaction will deliver benefits for even more patients and their families.

**Next Steps: Business as Usual**

While we are announcing this transaction today, it is only day one. We expect the transaction to close by the fourth quarter of 2025, subject to the satisfaction of the conditions in the merger agreement, completion of the cash tender offer by SERB for our shares and certain other closing conditions.

Between now and then, we remain an independent, publicly traded company, and it is business as usual for all of us. Patients are still counting on your important work, so we ask that you stay focused on your daily responsibilities.

We will be working with the SERB team to determine how we will bring our companies together. Many of the forward-looking decisions around the business will be made following the closing of this transaction. We will provide updates as we move forward and have news to share.

Please join me for an All-Employee Town Hall at 10:00 AM ET today – an invitation will be sent to all employees shortly. In the meantime, we have attached a "Frequently Asked Questions" document to help address questions you may have. You may also reach out to your manager or me directly at any time if you have further questions.

Finally, as a reminder, announcements like these are likely to draw increased media attention and may lead to inquiries from outside parties. As always, it is important that we speak with one voice. If you are contacted regarding today's news, please do not respond and simply forward all inquiries to our Head of IR, Courtney Dugan, <u>cdu@ymabs.com</u>.

On behalf of the Board and management team, thank you for everything you've done – and continue to do – to support our company and the patients and customers we serve. We are connected by one set of shared values and our commitment to serving our patients.

Sincerely,

Mike

**Forward-Looking Statements**

This communication contains forward-looking statements that involve risks and uncertainties relating to future events and the future performance of Y-mAbs and Serb, including statements relating to the ability to complete and the timing of completion of the transactions contemplated by the Agreement and Plan of Merger dated as of August 4, 2025 by and among Y-mAbs, Serb, and the other parties thereto (the "Merger Agreement"), including the anticipated occurrence, manner and timing of the proposed tender offer, the parties' ability to satisfy the conditions to the consummation of the tender offer and the other conditions to the consummation of the subsequent merger set forth in the Merger Agreement, the possibility of any termination of the Merger Agreement, and the prospective benefits of the proposed transaction, and other statements that are not historical facts. The forward-looking statements contained in this email are based on current expectations and assumptions that are subject to risks and uncertainties which may cause actual results to differ materially from the forward-looking statements. These statements may contain words such as "may," "will," "would," "could," "expect," "anticipate," "intend," "plan," "believe," "estimate," "project," "seek," "should," "strategy," "future," "opportunity," "potential" or other similar words and expressions indicating future results. Risks that may cause these forward-looking statements to be inaccurate include, without limitation: uncertainties as to the timing of the tender offer; uncertainties as to how many of Y-mAbs's stockholders will tender their stock in the offer; the possibility that competing offers or acquisition proposals will be made; the possibility that various closing conditions for the transaction may not be satisfied or waived, including that a governmental entity may prohibit, delay, or refuse to grant approval for the consummation of the transaction (or only grant approval subject to adverse conditions or limitations); the difficulty of predicting the timing or outcome of regulatory approvals or actions, if any; the occurrence of any event, change or other circumstance that could give rise to the termination of the Merger Agreement; the possibility that the transaction does not close; risks related to the parties' ability to realize the anticipated benefits of the proposed transaction, including the possibility that the expected benefits from the proposed acquisition will not be realized or will not be realized within the expected time period and that Y-mAbs and Serb will not be integrated successfully or that such integration may be more difficult, time-consuming or costly than expected; the effects of the transaction on relationships with employees, customers, suppliers, other business partners or governmental entities; negative effects of this announcement or the consummation of the proposed transaction on the market price of Y-mAbs's common stock and/or Y-mAbs's operating results; significant transaction costs; unknown or inestimable liabilities; the risk of litigation and/or regulatory actions related to the proposed transaction; Serb's ability to fund the proposed transaction; obtaining and maintaining adequate coverage and reimbursement for products; the time-consuming and uncertain regulatory approval process; the costly and time-consuming pharmaceutical product development process and the uncertainty of clinical success, including risks related to failure or delays in successfully initiating or completing clinical trials and assessing patients; global economic, financial, and healthcare system disruptions and the current and potential future negative impacts to the parties' business operations and financial results; the sufficiency of the parties' cash flows and capital resources; the parties' ability to achieve targeted or expected future financial performance and results and the uncertainty of future tax, accounting and other provisions and estimates; and other risks and uncertainties affecting Y-mAbs and Serb, including those described from time to time under the caption "Risk Factors" and elsewhere in Y-mAbs's filings and reports with the U.S. Securities and Exchange Commission (the "SEC"), including Y-mAbs's Annual Report on Form 10-K for the fiscal year ended December 31, 2024 and Quarterly Report on Form 10-Q for the quarterly period ended March 31, 2025, as well as the Tender Offer Statement on Schedule TO and related tender offer documents to be filed by Serb and its acquisition subsidiary, and the Solicitation/Recommendation Statement on Schedule 14D-9 to be filed by Y-mAbs. Any forward-looking statements are made based on the current beliefs and judgments of Y-mAbs's and Serb's management, and the reader is cautioned not to rely on any forward-looking statements made by Y-mAbs or Serb. Except as required by law, Y-mAbs and Serb do not undertake any obligation to update (publicly or otherwise) any forward-looking statement, including without limitation any financial projection or guidance, whether as a result of new information, future events, or otherwise.

**Important Information about the Tender Offer and Where to Find It**

The tender offer (the "Offer") for the Y-mAbs outstanding common stock referred to in this email has not yet commenced. The description contained in this email is neither an offer to purchase nor a solicitation of an offer to sell any securities, nor is it a substitute for the tender offer materials that Serb will file with the SEC. The solicitation and offer to purchase Y-mAbs's common stock will only be made pursuant to an offer to purchase and related tender offer materials. At the time the Offer is commenced, Serb will file a tender offer statement on Schedule TO and thereafter Y-mAbs will file a solicitation/recommendation statement on Schedule 14D-9 with the SEC with respect to the Offer.

THE TENDER OFFER MATERIALS (INCLUDING AN OFFER TO PURCHASE, A RELATED LETTER OF TRANSMITTAL AND CERTAIN OTHER OFFER DOCUMENTS) AND THE SOLICITATION/RECOMMENDATION STATEMENT ON SCHEDULE 14D-9, AS THEY MAY BE AMENDED OR SUPPLEMENTED FROM TIME TO TIME, WILL CONTAIN IMPORTANT INFORMATION. ANY HOLDERS OF Y-mAbs SHARES ARE URGED TO READ THESE DOCUMENTS CAREFULLY WHEN THEY BECOME AVAILABLE BECAUSE THEY WILL CONTAIN IMPORTANT INFORMATION THAT HOLDERS SHOULD CONSIDER BEFORE MAKING ANY DECISION REGARDING TENDERING THEIR SHARES.

The offer to purchase, the letter of transmittal, the solicitation/recommendation statement and related offer documents will be made available for free at the SEC's website at <u>www.sec.gov</u>. Copies of those offer documents and all other documents filed by Serb and Y-mAbs will be made available at no charge by directing a request to the information agent for the Offer, which will be named in the Schedule TO to be filed with the SEC. Copies of the solicitation/recommendation statement on Schedule 14D-9 to be filed with the SEC by Y-mAbs will be available free of charge on Y-mAbs's investor relations website at https://ir.ymabs.com/ or by contacting Y-mAbs's investor relations contact at <u>cdu@ymabs.com</u>.

In addition, Y-mAbs files annual, quarterly and current reports and other information with the SEC, which are also made available free of charge on the Company's investor relations website at https://ir.ymabs.com/ and at the SEC's website at www.sec.gov.

## Exhibit 99.3

**Exhibit 99.3**

**Y-mAbs Investor / Analyst Courtesy Letter**

**Subject:** Y-mAbs Agrees to be Acquired by SERB for $8.60 per Share

Good morning,

I'm pleased to share that Y-mAbs Therapeutics has entered into a definitive agreement under which SERB Pharmaceuticals has agreed to acquire Y-mAbs in a transaction with an equity value of $412 million.

Members of the management team will be available to answer questions. Please reach out to me to schedule a call.

Best Regards,

Courtney

**Forward-Looking Statements**

This communication contains forward-looking statements that involve risks and uncertainties relating to future events and the future performance of Y-mAbs and Serb, including statements relating to the ability to complete and the timing of completion of the transactions contemplated by the Agreement and Plan of Merger dated as of August 4, 2025 by and among Y-mAbs, Serb, and the other parties thereto (the "Merger Agreement"), including the anticipated occurrence, manner and timing of the proposed tender offer, the parties' ability to satisfy the conditions to the consummation of the tender offer and the other conditions to the consummation of the subsequent merger set forth in the Merger Agreement, the possibility of any termination of the Merger Agreement, and the prospective benefits of the proposed transaction, and other statements that are not historical facts. The forward-looking statements contained in this email are based on current expectations and assumptions that are subject to risks and uncertainties which may cause actual results to differ materially from the forward-looking statements. These statements may contain words such as "may," "will," "would," "could," "expect," "anticipate," "intend," "plan," "believe," "estimate," "project," "seek," "should," "strategy," "future," "opportunity," "potential" or other similar words and expressions indicating future results. Risks that may cause these forward-looking statements to be inaccurate include, without limitation: uncertainties as to the timing of the tender offer; uncertainties as to how many of Y-mAbs's stockholders will tender their stock in the offer; the possibility that competing offers or acquisition proposals will be made; the possibility that various closing conditions for the transaction may not be satisfied or waived, including that a governmental entity may prohibit, delay, or refuse to grant approval for the consummation of the transaction (or only grant approval subject to adverse conditions or limitations); the difficulty of predicting the timing or outcome of regulatory approvals or actions, if any; the occurrence of any event, change or other circumstance that could give rise to the termination of the Merger Agreement; the possibility that the transaction does not close; risks related to the parties' ability to realize the anticipated benefits of the proposed transaction, including the possibility that the expected benefits from the proposed acquisition will not be realized or will not be realized within the expected time period and that Y-mAbs and Serb will not be integrated successfully or that such integration may be more difficult, time-consuming or costly than expected; the effects of the transaction on relationships with employees, customers, suppliers, other business partners or governmental entities; negative effects of this announcement or the consummation of the proposed transaction on the market price of Y-mAbs's common stock and/or Y-mAbs's operating results; significant transaction costs; unknown or inestimable liabilities; the risk of litigation and/or regulatory actions related to the proposed transaction; Serb's ability to fund the proposed transaction; obtaining and maintaining adequate coverage and reimbursement for products; the time-consuming and uncertain regulatory approval process; the costly and time-consuming pharmaceutical product development process and the uncertainty of clinical success, including risks related to failure or delays in successfully initiating or completing clinical trials and assessing patients; global economic, financial, and healthcare system disruptions and the current and potential future negative impacts to the parties' business operations and financial results; the sufficiency of the parties' cash flows and capital resources; the parties' ability to achieve targeted or expected future financial performance and results and the uncertainty of future tax, accounting and other provisions and estimates; and other risks and uncertainties affecting Y-mAbs and Serb, including those described from time to time under the caption "Risk Factors" and elsewhere in Y-mAbs's filings and reports with the U.S. Securities and Exchange Commission (the "SEC"), including Y-mAbs's Annual Report on Form 10-K for the fiscal year ended December 31, 2024 and Quarterly Report on Form 10-Q for the quarterly period ended March 31, 2025, as well as the Tender Offer Statement on Schedule TO and related tender offer documents to be filed by Serb and its acquisition subsidiary, and the Solicitation/Recommendation Statement on Schedule 14D-9 to be filed by Y-mAbs. Any forward-looking statements are made based on the current beliefs and judgments of Y-mAbs's and Serb's management, and the reader is cautioned not to rely on any forward-looking statements made by Y-mAbs or Serb. Except as required by law, Y-mAbs and Serb do not undertake any obligation to update (publicly or otherwise) any forward-looking statement, including without limitation any financial projection or guidance, whether as a result of new information, future events, or otherwise.

**Important Information about the Tender Offer and Where to Find It**

The tender offer (the "Offer") for the Y-mAbs outstanding common stock referred to in this email has not yet commenced. The description contained in this email is neither an offer to purchase nor a solicitation of an offer to sell any securities, nor is it a substitute for the tender offer materials that Serb will file with the SEC. The solicitation and offer to purchase Y-mAbs's common stock will only be made pursuant to an offer to purchase and related tender offer materials. At the time the Offer is commenced, Serb will file a tender offer statement on Schedule TO and thereafter Y-mAbs will file a solicitation/recommendation statement on Schedule 14D-9 with the SEC with respect to the Offer.

THE TENDER OFFER MATERIALS (INCLUDING AN OFFER TO PURCHASE, A RELATED LETTER OF TRANSMITTAL AND CERTAIN OTHER OFFER DOCUMENTS) AND THE SOLICITATION/RECOMMENDATION STATEMENT ON SCHEDULE 14D-9, AS THEY MAY BE AMENDED OR SUPPLEMENTED FROM TIME TO TIME, WILL CONTAIN IMPORTANT INFORMATION. ANY HOLDERS OF Y-mAbs SHARES ARE URGED TO READ THESE DOCUMENTS CAREFULLY WHEN THEY BECOME AVAILABLE BECAUSE THEY WILL CONTAIN IMPORTANT INFORMATION THAT HOLDERS SHOULD CONSIDER BEFORE MAKING ANY DECISION REGARDING TENDERING THEIR SHARES.

The offer to purchase, the letter of transmittal, the solicitation/recommendation statement and related offer documents will be made available for free at the SEC's website at <u>www.sec.gov</u>. Copies of those offer documents and all other documents filed by Serb and Y-mAbs will be made available at no charge by directing a request to the information agent for the Offer, which will be named in the Schedule TO to be filed with the SEC. Copies of the solicitation/recommendation statement on Schedule 14D-9 to be filed with the SEC by Y-mAbs will be available free of charge on Y-mAbs's investor relations website at https://ir.ymabs.com/ or by contacting Y-mAbs's investor relations contact at <u>cdu@ymabs.com</u>.

In addition, Y-mAbs files annual, quarterly and current reports and other information with the SEC, which are also made available free of charge on the Company's investor relations website at https://ir.ymabs.com/ and at the SEC's website at www.sec.gov.

## Exhibit 99.4

**Exhibit 99.4**

**Y-mAbs Patient and Patient Advocacy Organizations Courtesy Letter** 

Hello,

I am reaching out with important news about Y-mAbs Therapeutics. Today, we announced that we have entered into a definitive agreement under which SERB Pharmaceuticals has agreed to acquire Y-mAbs.

Since our founding, patients have been the top priority for Y-mAbs. We recognize that our work with patients is critical as we further our mission of bringing important new cancer therapies to them as quickly as possible. We're as committed as ever to meeting our patients' needs, and our focus on providing life-changing medicines remains the same.

As you may know, SERB is a global specialty pharmaceutical company with a portfolio of critical medicines that treat complex and life-threatening conditions. By combining our expertise and resources with their specialty commercial capabilities, we can extend our shared commitment of improving the lives of even more patients and families on a global scale.

We believe that Y-mAbs has made important progress advancing DANYELZA® and our Radiopharmaceuticals platform. This transaction we are announcing today is the result of the Board of Directors' review of strategic alternatives to maximize value for Y-mAbs stockholders, with the assistance of external advisors.

We believe the transaction reflects the most attractive option available to Y-mAbs and provides significant, immediate and certain value to our stockholders. At the same time, we believe that the transaction will deliver benefits for even more patients and their families.

**Next Steps: Business as Usual**

We expect the transaction to close by the fourth quarter of 2025, subject to the completion of the tender offer by SERB for our shares and certain other closing conditions. Until then, we will continue to operate as a separate and independent company, and it is business as usual for Y-mAbs.

If you have any further questions, please do not hesitate to reach out to your normal company contact.

We value our relationship with you and the work you do to advocate for patients and their families.

Sincerely,

Michael Rossi

President and CEO

**Forward-Looking Statements**

This communication contains forward-looking statements that involve risks and uncertainties relating to future events and the future performance of Y-mAbs and Serb, including statements relating to the ability to complete and the timing of completion of the transactions contemplated by the Agreement and Plan of Merger dated as of August 4, 2025 by and among Y-mAbs, Serb, and the other parties thereto (the "Merger Agreement"), including the anticipated occurrence, manner and timing of the proposed tender offer, the parties' ability to satisfy the conditions to the consummation of the tender offer and the other conditions to the consummation of the subsequent merger set forth in the Merger Agreement, the possibility of any termination of the Merger Agreement, and the prospective benefits of the proposed transaction, and other statements that are not historical facts. The forward-looking statements contained in this email are based on current expectations and assumptions that are subject to risks and uncertainties which may cause actual results to differ materially from the forward-looking statements. These statements may contain words such as "may," "will," "would," "could," "expect," "anticipate," "intend," "plan," "believe," "estimate," "project," "seek," "should," "strategy," "future," "opportunity," "potential" or other similar words and expressions indicating future results. Risks that may cause these forward-looking statements to be inaccurate include, without limitation: uncertainties as to the timing of the tender offer; uncertainties as to how many of Y-mAbs's stockholders will tender their stock in the offer; the possibility that competing offers or acquisition proposals will be made; the possibility that various closing conditions for the transaction may not be satisfied or waived, including that a governmental entity may prohibit, delay, or refuse to grant approval for the consummation of the transaction (or only grant approval subject to adverse conditions or limitations); the difficulty of predicting the timing or outcome of regulatory approvals or actions, if any; the occurrence of any event, change or other circumstance that could give rise to the termination of the Merger Agreement; the possibility that the transaction does not close; risks related to the parties' ability to realize the anticipated benefits of the proposed transaction, including the possibility that the expected benefits from the proposed acquisition will not be realized or will not be realized within the expected time period and that Y-mAbs and Serb will not be integrated successfully or that such integration may be more difficult, time-consuming or costly than expected; the effects of the transaction on relationships with employees, customers, suppliers, other business partners or governmental entities; negative effects of this announcement or the consummation of the proposed transaction on the market price of Y-mAbs's common stock and/or Y-mAbs's operating results; significant transaction costs; unknown or inestimable liabilities; the risk of litigation and/or regulatory actions related to the proposed transaction; Serb's ability to fund the proposed transaction; obtaining and maintaining adequate coverage and reimbursement for products; the time-consuming and uncertain regulatory approval process; the costly and time-consuming pharmaceutical product development process and the uncertainty of clinical success, including risks related to failure or delays in successfully initiating or completing clinical trials and assessing patients; global economic, financial, and healthcare system disruptions and the current and potential future negative impacts to the parties' business operations and financial results; the sufficiency of the parties' cash flows and capital resources; the parties' ability to achieve targeted or expected future financial performance and results and the uncertainty of future tax, accounting and other provisions and estimates; and other risks and uncertainties affecting Y-mAbs and Serb, including those described from time to time under the caption "Risk Factors" and elsewhere in Y-mAbs's filings and reports with the U.S. Securities and Exchange Commission (the "SEC"), including Y-mAbs's Annual Report on Form 10-K for the fiscal year ended December 31, 2024 and Quarterly Report on Form 10-Q for the quarterly period ended March 31, 2025, as well as the Tender Offer Statement on Schedule TO and related tender offer documents to be filed by Serb and its acquisition subsidiary, and the Solicitation/Recommendation Statement on Schedule 14D-9 to be filed by Y-mAbs. Any forward-looking statements are made based on the current beliefs and judgments of Y-mAbs's and Serb's management, and the reader is cautioned not to rely on any forward-looking statements made by Y-mAbs or Serb. Except as required by law, Y-mAbs and Serb do not undertake any obligation to update (publicly or otherwise) any forward-looking statement, including without limitation any financial projection or guidance, whether as a result of new information, future events, or otherwise.

**Important Information about the Tender Offer and Where to Find It**

The tender offer (the "Offer") for the Y-mAbs outstanding common stock referred to in this email has not yet commenced. The description contained in this email is neither an offer to purchase nor a solicitation of an offer to sell any securities, nor is it a substitute for the tender offer materials that Serb will file with the SEC. The solicitation and offer to purchase Y-mAbs's common stock will only be made pursuant to an offer to purchase and related tender offer materials. At the time the Offer is commenced, Serb will file a tender offer statement on Schedule TO and thereafter Y-mAbs will file a solicitation/recommendation statement on Schedule 14D-9 with the SEC with respect to the Offer.

THE TENDER OFFER MATERIALS (INCLUDING AN OFFER TO PURCHASE, A RELATED LETTER OF TRANSMITTAL AND CERTAIN OTHER OFFER DOCUMENTS) AND THE SOLICITATION/RECOMMENDATION STATEMENT ON SCHEDULE 14D-9, AS THEY MAY BE AMENDED OR SUPPLEMENTED FROM TIME TO TIME, WILL CONTAIN IMPORTANT INFORMATION. ANY HOLDERS OF Y-mAbs SHARES ARE URGED TO READ THESE DOCUMENTS CAREFULLY WHEN THEY BECOME AVAILABLE BECAUSE THEY WILL CONTAIN IMPORTANT INFORMATION THAT HOLDERS SHOULD CONSIDER BEFORE MAKING ANY DECISION REGARDING TENDERING THEIR SHARES.

The offer to purchase, the letter of transmittal, the solicitation/recommendation statement and related offer documents will be made available for free at the SEC's website at <u>www.sec.gov</u>. Copies of those offer documents and all other documents filed by Serb and Y-mAbs will be made available at no charge by directing a request to the information agent for the Offer, which will be named in the Schedule TO to be filed with the SEC. Copies of the solicitation/recommendation statement on Schedule 14D-9 to be filed with the SEC by Y-mAbs will be available free of charge on Y-mAbs's investor relations website at https://ir.ymabs.com/ or by contacting Y-mAbs's investor relations contact at <u>cdu@ymabs.com</u>.

In addition, Y-mAbs files annual, quarterly and current reports and other information with the SEC, which are also made available free of charge on the Company's investor relations website at https://ir.ymabs.com/ and at the SEC's website at www.sec.gov.

## Exhibit 99.5

**Exhibit 99.5**

**Y-mAbs Vendor / Supplier Courtesy Letter**

Dear Valued Partner,

I am reaching out with important news about Y-mAbs Therapeutics. Today, we announced that we have entered into a definitive agreement under which SERB Pharmaceuticals has agreed to acquire Y-mAbs.

Since our founding, patients have been the top priority for Y-mAbs. We recognize that our work with patients is critical as we further our mission of bringing important new cancer therapies to them as quickly as possible. We're as committed as ever to meeting our patients' needs, and our focus on providing life-changing medicines remains the same.

As you may know, SERB is a global specialty pharmaceutical company with a portfolio of critical medicines that treat complex and life-threatening conditions. By combining our expertise and resources with their specialty commercial capabilities, we can extend our shared commitment of improving the lives of even more patients and families on a global scale.

We believe that Y-mAbs has made important progress advancing DANYELZA® and our Radiopharmaceuticals platform. This transaction we are announcing today is the result of the Board of Directors' review of strategic alternatives to maximize value for Y-mAbs stockholders, with the assistance of external advisors.

We believe the transaction reflects the most attractive option available to Y-mAbs and provides significant, immediate and certain value to our stockholders. At the same time, we believe that the transaction will deliver benefits for even more patients and their families.

**Next Steps: Business as Usual**

We expect the transaction to close by the fourth quarter of 2025, subject to the completion of the tender offer by SERB for our shares and certain other closing conditions. Until then, we will continue to operate as a separate and independent company, and it is business as usual for Y-mAbs.

If you have any further questions, please do not hesitate to reach out to your normal company contact.

Sincerely,

Michael Rossi

President and CEO<br>

**Forward-Looking Statements**

This communication contains forward-looking statements that involve risks and uncertainties relating to future events and the future performance of Y-mAbs and Serb, including statements relating to the ability to complete and the timing of completion of the transactions contemplated by the Agreement and Plan of Merger dated as of August 4, 2025 by and among Y-mAbs, Serb, and the other parties thereto (the "Merger Agreement"), including the anticipated occurrence, manner and timing of the proposed tender offer, the parties' ability to satisfy the conditions to the consummation of the tender offer and the other conditions to the consummation of the subsequent merger set forth in the Merger Agreement, the possibility of any termination of the Merger Agreement, and the prospective benefits of the proposed transaction, and other statements that are not historical facts. The forward-looking statements contained in this email are based on current expectations and assumptions that are subject to risks and uncertainties which may cause actual results to differ materially from the forward-looking statements. These statements may contain words such as "may," "will," "would," "could," "expect," "anticipate," "intend," "plan," "believe," "estimate," "project," "seek," "should," "strategy," "future," "opportunity," "potential" or other similar words and expressions indicating future results. Risks that may cause these forward-looking statements to be inaccurate include, without limitation: uncertainties as to the timing of the tender offer; uncertainties as to how many of Y-mAbs's stockholders will tender their stock in the offer; the possibility that competing offers or acquisition proposals will be made; the possibility that various closing conditions for the transaction may not be satisfied or waived, including that a governmental entity may prohibit, delay, or refuse to grant approval for the consummation of the transaction (or only grant approval subject to adverse conditions or limitations); the difficulty of predicting the timing or outcome of regulatory approvals or actions, if any; the occurrence of any event, change or other circumstance that could give rise to the termination of the Merger Agreement; the possibility that the transaction does not close; risks related to the parties' ability to realize the anticipated benefits of the proposed transaction, including the possibility that the expected benefits from the proposed acquisition will not be realized or will not be realized within the expected time period and that Y-mAbs and Serb will not be integrated successfully or that such integration may be more difficult, time-consuming or costly than expected; the effects of the transaction on relationships with employees, customers, suppliers, other business partners or governmental entities; negative effects of this announcement or the consummation of the proposed transaction on the market price of Y-mAbs's common stock and/or Y-mAbs's operating results; significant transaction costs; unknown or inestimable liabilities; the risk of litigation and/or regulatory actions related to the proposed transaction; Serb's ability to fund the proposed transaction; obtaining and maintaining adequate coverage and reimbursement for products; the time-consuming and uncertain regulatory approval process; the costly and time-consuming pharmaceutical product development process and the uncertainty of clinical success, including risks related to failure or delays in successfully initiating or completing clinical trials and assessing patients; global economic, financial, and healthcare system disruptions and the current and potential future negative impacts to the parties' business operations and financial results; the sufficiency of the parties' cash flows and capital resources; the parties' ability to achieve targeted or expected future financial performance and results and the uncertainty of future tax, accounting and other provisions and estimates; and other risks and uncertainties affecting Y-mAbs and Serb, including those described from time to time under the caption "Risk Factors" and elsewhere in Y-mAbs's filings and reports with the U.S. Securities and Exchange Commission (the "SEC"), including Y-mAbs's Annual Report on Form 10-K for the fiscal year ended December 31, 2024 and Quarterly Report on Form 10-Q for the quarterly period ended March 31, 2025, as well as the Tender Offer Statement on Schedule TO and related tender offer documents to be filed by Serb and its acquisition subsidiary, and the Solicitation/Recommendation Statement on Schedule 14D-9 to be filed by Y-mAbs. Any forward-looking statements are made based on the current beliefs and judgments of Y-mAbs's and Serb's management, and the reader is cautioned not to rely on any forward-looking statements made by Y-mAbs or Serb. Except as required by law, Y-mAbs and Serb do not undertake any obligation to update (publicly or otherwise) any forward-looking statement, including without limitation any financial projection or guidance, whether as a result of new information, future events, or otherwise.

**Important Information about the Tender Offer and Where to Find It**

The tender offer (the "Offer") for the Y-mAbs outstanding common stock referred to in this email has not yet commenced. The description contained in this email is neither an offer to purchase nor a solicitation of an offer to sell any securities, nor is it a substitute for the tender offer materials that Serb will file with the SEC. The solicitation and offer to purchase Y-mAbs's common stock will only be made pursuant to an offer to purchase and related tender offer materials. At the time the Offer is commenced, Serb will file a tender offer statement on Schedule TO and thereafter Y-mAbs will file a solicitation/recommendation statement on Schedule 14D-9 with the SEC with respect to the Offer.

THE TENDER OFFER MATERIALS (INCLUDING AN OFFER TO PURCHASE, A RELATED LETTER OF TRANSMITTAL AND CERTAIN OTHER OFFER DOCUMENTS) AND THE SOLICITATION/RECOMMENDATION STATEMENT ON SCHEDULE 14D-9, AS THEY MAY BE AMENDED OR SUPPLEMENTED FROM TIME TO TIME, WILL CONTAIN IMPORTANT INFORMATION. ANY HOLDERS OF Y-mAbs SHARES ARE URGED TO READ THESE DOCUMENTS CAREFULLY WHEN THEY BECOME AVAILABLE BECAUSE THEY WILL CONTAIN IMPORTANT INFORMATION THAT HOLDERS SHOULD CONSIDER BEFORE MAKING ANY DECISION REGARDING TENDERING THEIR SHARES.

The offer to purchase, the letter of transmittal, the solicitation/recommendation statement and related offer documents will be made available for free at the SEC's website at <u>www.sec.gov</u>. Copies of those offer documents and all other documents filed by Serb and Y-mAbs will be made available at no charge by directing a request to the information agent for the Offer, which will be named in the Schedule TO to be filed with the SEC. Copies of the solicitation/recommendation statement on Schedule 14D-9 to be filed with the SEC by Y-mAbs will be available free of charge on Y-mAbs's investor relations website at https://ir.ymabs.com/ or by contacting Y-mAbs's investor relations contact at <u>cdu@ymabs.com</u>.

In addition, Y-mAbs files annual, quarterly and current reports and other information with the SEC, which are also made available free of charge on the Company's investor relations website at https://ir.ymabs.com/ and at the SEC's website at www.sec.gov.

## Exhibit 99.6

**Exhibit 99.6**

**Y-mAbs LinkedIn Post**

![](tm2522599d1_ex99-8img001.jpg)

**Forward-Looking Statements**

This communication contains forward-looking statements that involve risks and uncertainties relating to future events and the future performance of Y-mAbs and Serb, including statements relating to the ability to complete and the timing of completion of the transactions contemplated by the Agreement and Plan of Merger dated as of August 4, 2025 by and among Y-mAbs, Serb, and the other parties thereto (the "Merger Agreement"), including the anticipated occurrence, manner and timing of the proposed tender offer, the parties' ability to satisfy the conditions to the consummation of the tender offer and the other conditions to the consummation of the subsequent merger set forth in the Merger Agreement, the possibility of any termination of the Merger Agreement, and the prospective benefits of the proposed transaction, and other statements that are not historical facts. The forward-looking statements contained in this email are based on current expectations and assumptions that are subject to risks and uncertainties which may cause actual results to differ materially from the forward-looking statements. These statements may contain words such as "may," "will," "would," "could," "expect," "anticipate," "intend," "plan," "believe," "estimate," "project," "seek," "should," "strategy," "future," "opportunity," "potential" or other similar words and expressions indicating future results. Risks that may cause these forward-looking statements to be inaccurate include, without limitation: uncertainties as to the timing of the tender offer; uncertainties as to how many of Y-mAbs's stockholders will tender their stock in the offer; the possibility that competing offers or acquisition proposals will be made; the possibility that various closing conditions for the transaction may not be satisfied or waived, including that a governmental entity may prohibit, delay, or refuse to grant approval for the consummation of the transaction (or only grant approval subject to adverse conditions or limitations); the difficulty of predicting the timing or outcome of regulatory approvals or actions, if any; the occurrence of any event, change or other circumstance that could give rise to the termination of the Merger Agreement; the possibility that the transaction does not close; risks related to the parties' ability to realize the anticipated benefits of the proposed transaction, including the possibility that the expected benefits from the proposed acquisition will not be realized or will not be realized within the expected time period and that Y-mAbs and Serb will not be integrated successfully or that such integration may be more difficult, time-consuming or costly than expected; the effects of the transaction on relationships with employees, customers, suppliers, other business partners or governmental entities; negative effects of this announcement or the consummation of the proposed transaction on the market price of Y-mAbs's common stock and/or Y-mAbs's operating results; significant transaction costs; unknown or inestimable liabilities; the risk of litigation and/or regulatory actions related to the proposed transaction; Serb's ability to fund the proposed transaction; obtaining and maintaining adequate coverage and reimbursement for products; the time-consuming and uncertain regulatory approval process; the costly and time-consuming pharmaceutical product development process and the uncertainty of clinical success, including risks related to failure or delays in successfully initiating or completing clinical trials and assessing patients; global economic, financial, and healthcare system disruptions and the current and potential future negative impacts to the parties' business operations and financial results; the sufficiency of the parties' cash flows and capital resources; the parties' ability to achieve targeted or expected future financial performance and results and the uncertainty of future tax, accounting and other provisions and estimates; and other risks and uncertainties affecting Y-mAbs and Serb, including those described from time to time under the caption "Risk Factors" and elsewhere in Y-mAbs's filings and reports with the U.S. Securities and Exchange Commission (the "SEC"), including Y-mAbs's Annual Report on Form 10-K for the fiscal year ended December 31, 2024 and Quarterly Report on Form 10-Q for the quarterly period ended March 31, 2025, as well as the Tender Offer Statement on Schedule TO and related tender offer documents to be filed by Serb and its acquisition subsidiary, and the Solicitation/Recommendation Statement on Schedule 14D-9 to be filed by Y-mAbs. Any forward-looking statements are made based on the current beliefs and judgments of Y-mAbs's and Serb's management, and the reader is cautioned not to rely on any forward-looking statements made by Y-mAbs or Serb. Except as required by law, Y-mAbs and Serb do not undertake any obligation to update (publicly or otherwise) any forward-looking statement, including without limitation any financial projection or guidance, whether as a result of new information, future events, or otherwise.

**Important Information about the Tender Offer and Where to Find It**

The tender offer (the "Offer") for the Y-mAbs outstanding common stock referred to in this email has not yet commenced. The description contained in this email is neither an offer to purchase nor a solicitation of an offer to sell any securities, nor is it a substitute for the tender offer materials that Serb will file with the SEC. The solicitation and offer to purchase Y-mAbs's common stock will only be made pursuant to an offer to purchase and related tender offer materials. At the time the Offer is commenced, Serb will file a tender offer statement on Schedule TO and thereafter Y-mAbs will file a solicitation/recommendation statement on Schedule 14D-9 with the SEC with respect to the Offer.

THE TENDER OFFER MATERIALS (INCLUDING AN OFFER TO PURCHASE, A RELATED LETTER OF TRANSMITTAL AND CERTAIN OTHER OFFER DOCUMENTS) AND THE SOLICITATION/RECOMMENDATION STATEMENT ON SCHEDULE 14D-9, AS THEY MAY BE AMENDED OR SUPPLEMENTED FROM TIME TO TIME, WILL CONTAIN IMPORTANT INFORMATION. ANY HOLDERS OF Y-mAbs SHARES ARE URGED TO READ THESE DOCUMENTS CAREFULLY WHEN THEY BECOME AVAILABLE BECAUSE THEY WILL CONTAIN IMPORTANT INFORMATION THAT HOLDERS SHOULD CONSIDER BEFORE MAKING ANY DECISION REGARDING TENDERING THEIR SHARES.

The offer to purchase, the letter of transmittal, the solicitation/recommendation statement and related offer documents will be made available for free at the SEC's website at <u>www.sec.gov</u>. Copies of those offer documents and all other documents filed by Serb and Y-mAbs will be made available at no charge by directing a request to the information agent for the Offer, which will be named in the Schedule TO to be filed with the SEC. Copies of the solicitation/recommendation statement on Schedule 14D-9 to be filed with the SEC by Y-mAbs will be available free of charge on Y-mAbs's investor relations website at https://ir.ymabs.com/ or by contacting Y-mAbs's investor relations contact at <u>cdu@ymabs.com</u>.

In addition, Y-mAbs files annual, quarterly and current reports and other information with the SEC, which are also made available free of charge on the Company's investor relations website at https://ir.ymabs.com/ and at the SEC's website at www.sec.gov.