# EDGAR Filing Document

**Accession Number:** 0001845337
**File Stem:** 0001104659-26-001116
**Filing Date:** 2026-1
**Character Count:** 18072
**Document Hash:** df0366e0e4ccd9f0cec45f3c77c7cf58
**Contains OCR:** False
**Source Format:** 

## Filing Content

## Filing Summary
**0001104659-26-001116.hdr.sgml**: 20260106

**ACCESSION NUMBER**: 0001104659-26-001116

**CONFORMED SUBMISSION TYPE**: SC TO-T/A

**PUBLIC DOCUMENT COUNT**: 3

**FILED AS OF DATE**: 20260106

**DATE AS OF CHANGE**: 20260106

**GROUP MEMBERS**: EMERALD MERGER SUB, INC.

**SUBJECT COMPANY**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** Mersana Therapeutics, Inc.
- **CENTRAL INDEX KEY:** 0001442836
- **STANDARD INDUSTRIAL CLASSIFICATION:** PHARMACEUTICAL PREPARATIONS [2834]
- **ORGANIZATION NAME:** 03 Life Sciences
- **EIN:** 000000000
- **STATE OF INCORPORATION:** DE
- **FISCAL YEAR END:** 1231

**FILING VALUES:**
- **FORM TYPE:** SC TO-T/A
- **SEC ACT:** 1934 Act
- **SEC FILE NUMBER:** 005-90033
- **FILM NUMBER:** 26509555

**BUSINESS ADDRESS:**
- **STREET 1:** 840 MEMORIAL DRIVE
- **CITY:** CAMBRIDGE
- **STATE:** MA
- **ZIP:** 02139
- **BUSINESS PHONE:** 617-498-0020

**MAIL ADDRESS:**
- **STREET 1:** 840 MEMORIAL DRIVE
- **CITY:** CAMBRIDGE
- **STATE:** MA
- **ZIP:** 02139

**FORMER COMPANY:**
- **FORMER CONFORMED NAME:** MERSANA THERAPEUTICS INC
- **DATE OF NAME CHANGE:** 20080813
**FILED BY**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** Day One Biopharmaceuticals, Inc.
- **CENTRAL INDEX KEY:** 0001845337
- **STANDARD INDUSTRIAL CLASSIFICATION:** PHARMACEUTICAL PREPARATIONS [2834]
- **ORGANIZATION NAME:** 03 Life Sciences
- **EIN:** 832415215
- **STATE OF INCORPORATION:** DE
- **FISCAL YEAR END:** 1231

**FILING VALUES:**
- **FORM TYPE:** SC TO-T/A

**BUSINESS ADDRESS:**
- **STREET 1:** 1800 SIERRA POINT PARKWAY, SUITE 200
- **CITY:** BRISBANE
- **STATE:** CA
- **ZIP:** 94005
- **BUSINESS PHONE:** 650 484-0899

**MAIL ADDRESS:**
- **STREET 1:** 1800 SIERRA POINT PARKWAY, SUITE 200
- **CITY:** BRISBANE
- **STATE:** CA
- **ZIP:** 94005

**FORMER COMPANY:**
- **FORMER CONFORMED NAME:** Day One Biopharmaceuticals Holding Co LLC
- **DATE OF NAME CHANGE:** 20210209

**UNITED STATES<br> SECURITIES AND EXCHANGE COMMISSION**

**Washington, D.C. 20549**

**SCHEDULE TO**

**Tender Offer Statement under Section 14(d)(1) or 13(e)(1)<br> of the Securities Exchange Act of 1934**

**(Amendment No. 2)**

**MERSANA THERAPEUTICS, INC.**

(Name of Subject Company (issuer))

**EMERALD MERGER SUB, INC.**

(Offeror)

**a direct wholly owned subsidiary of**

**DAY ONE BIOPHARMACEUTICALS, INC.**

(Parent of Offeror) <br> (Names of Filing Persons (identifying status as offeror, issuer or other person))

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

(Title of Class of Securities)

**59045L 106**

(CUSIP Number of Class of Securities)

**Adam Dubow<br> General Counsel<br> Day One Biopharmaceuticals, Inc.<br> 1800 Sierra Point Parkway, Suite 200<br> Brisbane, California 94005<br> Telephone: (650) 484-0899**

(Name, address, and telephone numbers of person authorized to receive notices and communications on behalf of filing persons)

***Copy to:***

**Robert A. Freedman<br> David Michaels<br> Julia Forbess<br> Fenwick & West LLP<br> 401 Union Street, Floor 5**

**Seattle, WA 98101**

**Telephone: (206) 389-4510**

◻ Check the box if the filing relates solely to preliminary communications made before the commencement of a tender offer.

Check the appropriate boxes below to designate any transactions to which the statement relates:

⌧ Third-party tender offer subject to Rule 14d-1.

¨ Issuer tender offer subject to Rule 13e-4.

◻ Going-private transaction subject to Rule 13e-3.

¨ Amendment to Schedule 13D under Rule 13d-2.

Check the following box if the filing is a final amendment reporting the results of the tender offer: ☒

If applicable, check the appropriate box(es) below to designate the appropriate rule provision(s) relied upon:

◻ Rule 13e-4(i) (Cross-Border Issuer Tender Offer)

◻ Rule 14d-1(d) (Cross-Border Third-Party Tender Offer)

This Amendment No. 2 ("Amendment No. 2") to the Tender Offer Statement on Schedule TO (together with any amendments and supplements thereto, the "Schedule TO") amends and supplements the Tender Offer Statement originally filed with the U.S. Securities and Exchange Commission (the "SEC") on December 5, 2025 by Day One Biopharmaceuticals, Inc., a Delaware corporation ("Day One"), and Emerald Merger Sub, Inc., a Delaware corporation and a direct wholly owned subsidiary of Day One (the "Purchaser"). This Amendment No. 2 and the Schedule TO relate to the offer by Purchaser to purchase all of the issued and outstanding shares of common stock, par value $0.0001 per share (the "Shares"), of Mersana Therapeutics, Inc., a Delaware corporation ("Mersana"), which constitute all of the issued and outstanding shares of capital stock of Mersana, at a purchase price of (i) $25.00 per Share, net to the stockholder in cash, without interest and less any applicable tax withholding, plus (ii) one non-tradable contingent value right (each a "CVR") per Share, representing the right to receive certain contingent payments of up to an aggregate amount of $30.25 per CVR in cash, without interest, less any applicable tax withholding, upon the achievement of certain specified milestones on or prior to the applicable milestone outside dates in accordance with the terms and conditions set forth in the Contingent Value Rights Agreement, to be entered into with Computershare Trust Company, N.A., a Delaware corporation, upon the terms and subject to the conditions set forth in the Offer to Purchase, dated and filed with the SEC on December 5, 2025 (as it may be amended or supplemented from time to time, the "Offer to Purchase"), and in the related Letter of Transmittal (as it may be amended or supplemented from time to time, the "Letter of Transmittal"), copies of which are filed with the Schedule TO as Exhibits (a)(1)(A) and (a)(1)(B), respectively.

Capitalized terms used, but not otherwise defined herein shall have the respective meanings ascribed to them in the Offer to Purchase. The information set forth in the Schedule TO remains unchanged and is incorporated herein by reference, except that such information is hereby amended or supplemented to the extent specifically provided herein.

***Items 1 through 9 and Item 11.***

The Offer to Purchase and Items 1 through 9 and Item 11 of the Schedule TO, to the extent such Items incorporate by reference the information contained in the Offer to Purchase, are hereby amended and supplemented to include the following:

"The Offer and withdrawal rights expired as scheduled at one minute past 11:59 p.m. Eastern time, on January 5, 2026 (the "Expiration Date"). The Depositary has advised Purchaser that, as of the Expiration Date, 3,029,135 Shares were validly tendered (and not validly withdrawn) pursuant to the Offer, representing approximately 60.57% of the total outstanding Shares as of the Expiration Date. The number of Shares validly tendered and not validly withdrawn pursuant to the Offer satisfies the Minimum Condition.

All conditions to the Offer having been satisfied, on January 6, 2026, Day One irrevocably accepted for payment all Shares validly tendered (and not validly withdrawn) prior to the Expiration Date, and payment of the Offer Price for such Shares will be made promptly in accordance with the terms of the Offer and the Merger Agreement.

Promptly following the Expiration Date and Purchaser's acceptance for payment of the Shares pursuant to the Offer, Day One and Purchaser consummated the Merger pursuant to the terms of the Merger Agreement and without any action by the stockholders of Mersana in accordance with Section 251(h) of the DGCL. At the Effective Time, Purchaser was merged with and into Mersana, with Mersana continuing as the Surviving Corporation, and each Share that was issued and outstanding immediately prior to the Effective Time (other than Shares owned by Day One, Purchaser or Mersana or by any of their respective subsidiaries (or held in Mersana's treasury)) was cancelled and (other than any Dissenting Shares) was converted into the right to receive the Offer Price, without interest, subject to any applicable withholding of taxes. The Shares will no longer be listed on Nasdaq and will be deregistered under the Exchange Act.

On January 6, 2026, Day One issued a press release announcing the expiration and results of the Offer and the consummation of the Merger. The full text of the press release is included as Exhibit (a)(5)(H) hereto and is incorporated herein by reference."

***Item 12. Exhibits.***

Item 12 of the Schedule TO is hereby amended and supplemented by adding the following exhibit:

<u>Index No.</u> <u>Description</u> <br> [(a)(5)(H)\*\*](tm2534581d1_ex99-a5h.htm) [Press Release issued by Day One, dated January 6, 2026.](tm2534581d1_ex99-a5h.htm)

**SIGNATURES**

After due inquiry and to the best knowledge and belief of the undersigned, each of the undersigned certifies that the information set forth in this statement is true, complete and correct.

---

| |
|:---|
| Date: January 6, 2026 |
| **EMERALD MERGER SUB, INC.** |
| /s/ Charles N. York II  |
| Name: Charles N. York II, M.B.A. |
| Title: Chief Executive Officer and President |
| **DAY ONE BIOPHARMACEUTICALS, INC.** |
| /s/ Jeremy Bender  |
| Name: Jeremy Bender, Ph.D., M.B.A. |
| Title: Chief Executive Officer and President |

---

## Ex-99.(A)(5)(H)

**Exhibit (a)(5)(H)**

![](tm2534581d1_exa5himg001.jpg)

**Day One Completes Acquisition of Mersana Therapeutics**

*Acquisition expands Day One's pipeline with clinical-stage antibody drug conjugate (ADC) emiltatug ledadotin (Emi-Le) targeting rare cancer adenoid cystic carcinoma (ACC)*

**BRISBANE, Calif., JANUARY 6, 2026 –** Day One Biopharmaceuticals, Inc. (Nasdaq: DAWN) ("Day One"), a biopharmaceutical company dedicated to developing and commercializing targeted therapies for people of all ages with life-threatening diseases, today announced the successful close of its acquisition of Mersana Therapeutics, Inc., (NASDAQ: MRSN) ("Mersana") following completion of all conditions of the tender offer to acquire all outstanding shares of Mersana at a price of $25 per share in cash, plus one non-tradable contingent value right ("CVR") per share to receive certain potential milestone payments of up to an aggregate of $30.25 per CVR in cash.

"This acquisition of Mersana is a strategic fit with Day One's mission and ambitions, allowing us to continue to expand into adult oncology while maintaining a focus on rare cancers. With promising early clinical data, Emi-Le represents a potentially transformative advancement in the treatment of ACC, and we will leverage our distinct capabilities to rapidly develop the asset and pursue registration to reach patient communities who have no approved therapies today," said Jeremy Bender, Ph.D., chief executive officer of Day One. "Building on the strong momentum of OJEMDA in the market and our continually progressing pipeline, this acquisition strengthens our overall position to expand our impact on patient communities while delivering sustainable business growth."

Through this acquisition, Day One has added a second novel ADC to the company's clinical pipeline. Emi-Le (emiltatug ledadotin) represents an innovative and differentiated ADC directed against B7-H4, a well-characterized target in certain cancers including adenoid cystic carcinoma (ACC), a challenging rare cancer usually arising within the salivary gland with a clear unmet medical need. For additional background on Emi-Le and the acquisition, please read the announcement <u>press release</u> and view Day One's <u>investor presentation</u>.

**Terms of the Acquisition**

Day One has acquired all outstanding shares of Mersana common stock at a price of $25 per share in cash, plus one non-tradable CVR per share to receive certain potential milestone payments of up to an aggregate of $30.25 per CVR in cash, for total consideration of up to $55.25 per share in cash. The CVR is payable subject to certain terms and conditions of achievement of specified milestones.

The tender offer expired as scheduled at one minute following 11:59 p.m., Eastern Time, on January 5, 2026 (the "Expiration Date"). The depositary for the tender offer, Computershare Trust Company, N.A., advised Day One that, as of the Expiration Date, a total of 3,029,135 shares of Mersana common stock were validly tendered and not validly withdrawn pursuant to the tender offer, representing 60.57% of the outstanding shares of Mersana common stock and satisfying the minimum condition to consummate the tender offer. All of the conditions of the tender offer having been satisfied, Day One accepted for payment all such tendered shares, and following a statutory merger under Section 251(h) of the Delaware General Corporation Law on January 6, 2026, Mersana became a direct wholly owned subsidiary of Day One. All remaining shares of Mersana common stock that were not tendered in the tender offer were converted into the right to receive the same per share consideration as shares that were tendered in the tender offer, as described above. With the completion of the acquisition, Mersana's common stock will cease to trade on the Nasdaq stock exchange prior to market open on January 6, 2026 and Mersana's common stock will be delisted from Nasdaq.

**Advisors**

Gordon Dyal & Co., LLC acted as the exclusive financial advisor to Day One, with Fenwick & West LLP serving as legal counsel. TD Cowen acted as financial advisor to Mersana, with Wilmer Cutler Pickering Hale and Dorr LLP serving as legal counsel.

**About Day One Biopharmaceuticals**

Day One Biopharmaceuticals is a commercial-stage biopharmaceutical company that believes when it comes to pediatric cancer, we can do better. The Company was founded to address a critical unmet need: the dire lack of therapeutic development in pediatric cancer. Inspired by "The Day One Talk" that physicians have with patients and their families about an initial cancer diagnosis and treatment plan, Day One aims to re-envision cancer drug development and redefine what's possible for all people living with cancer—regardless of age—starting from Day One.

Day One partners with leading clinical oncologists, families, and scientists to identify, acquire, and develop important targeted cancer treatments. Day One's pipeline includes tovorafenib (OJEMDA™), DAY301, and following the January 2026 acquisition of Mersana Therapeutics, Emi-Le (emiltatug ledadotin), a novel antibody drug conjugate (ADC) targeting the B7-H4 protein in clinical development to treat the rare cancer adenoid cystic carcinoma (ACC).

Day One is based in Brisbane, California. For more information, please visit <u>www.dayonebio.com</u> or find Day One on <u>LinkedIn</u> or <u>X</u>.

Day One uses its Investor Relations website (ir.dayonebio.com), its X handle (x.com/DayOneBio), and LinkedIn Home Page (linkedin.com/company/dayonebio) as a means of disseminating or providing notification of, among other things, news or announcements regarding its business or financial performance, investor events, press releases, and earnings releases, and as a means of disclosing material nonpublic information and for complying with its disclosure obligations under Regulation FD.

**Cautionary Note Regarding Forward-Looking Statements**

This press release contains "forward-looking" statements, including, but not limited to: Day One's plans to develop and commercialize cancer therapies and its pipeline, including the ability of Emi-Le to treat ACC or other cancers, statements regarding the payment and timing of payment of the offer to former Mersana common stockholders, the ability and timing of delisting of Mersana common stock, and the ability to achieve any milestones under the CVR within the milestone payment period under the CVR. Statements including words such as "believe," "plan," "continue," "expect," "will," "develop," "signal," "potential," or "ongoing" and statements in the future tense are forward-looking statements. These forward-looking statements involve risks and uncertainties, as well as assumptions, which, if they do not fully materialize or prove incorrect, could cause our results to differ materially from those expressed or implied by such forward-looking statements.

Forward-looking statements are subject to risks and uncertainties that may cause Day One's actual activities or results to differ significantly from those expressed in any forward-looking statement, including risks and uncertainties in this press release and other risks set forth in our filings with the Securities and Exchange Commission, including risks related to the ability to realize the anticipated benefits of the acquisition, including the possibility that the expected benefits from the acquisition will not be realized or will not be realized within the expected time period; the risk that the businesses will not be integrated successfully; disruption from the transaction making it more difficult to maintain business and operational relationships; negative effects of the consummation of the acquisition on the market price of Day One's common stock and/or operating results; significant transaction costs; unknown liabilities; Day One's ability to develop, obtain and retain regulatory approval for or commercialize any product candidate; Day One's ability to protect intellectual property; the potential impact of global business or macroeconomic conditions, including as a result of inflation, rising interest rates, instability in the global banking system, geopolitical conflicts and the sufficiency of Day One's cash, cash equivalents and investments to fund its operations. These forward-looking statements speak only as of the date hereof and Day One specifically disclaims any obligation to update these forward-looking statements or reasons why actual results might differ, whether as a result of new information, future events or otherwise, except as required by law.

**DAY ONE MEDIA**

<u>media@dayonebio.com</u>

**DAY ONE INVESTORS**

LifeSci Advisors, PJ Kelleher

<u>pkelleher@lifesciadvisors.com</u>

# # #