# EDGAR Filing Document

**Accession Number:** 0001745020
**File Stem:** 0000947871-23-000321
**Filing Date:** 2023-3
**Character Count:** 35671
**Document Hash:** 88f174523c6f9164b6e8fa190f3be082
**Contains OCR:** False
**Source Format:** 

## Filing Content

## Filing Summary
**0000947871-23-000321.hdr.sgml**: 20230314

**ACCESSION NUMBER**: 0000947871-23-000321

**CONFORMED SUBMISSION TYPE**: SC 13D/A

**PUBLIC DOCUMENT COUNT**: 2

**FILED AS OF DATE**: 20230314

**DATE AS OF CHANGE**: 20230314

**GROUP MEMBERS**: ORBIMED CAPITAL GP VII LLC

**GROUP MEMBERS**: ORBIMED GENESIS GP LLC

**SUBJECT COMPANY**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** Theseus Pharmaceuticals, Inc.
- **CENTRAL INDEX KEY:** 0001745020
- **STANDARD INDUSTRIAL CLASSIFICATION:** PHARMACEUTICAL PREPARATIONS [2834]
- **IRS NUMBER:** 830712806
- **STATE OF INCORPORATION:** DE
- **FISCAL YEAR END:** 1231

**FILING VALUES:**
- **FORM TYPE:** SC 13D/A
- **SEC ACT:** 1934 Act
- **SEC FILE NUMBER:** 005-92944
- **FILM NUMBER:** 23731262

**BUSINESS ADDRESS:**
- **STREET 1:** 314 MAIN STREET, SUITE 04-200
- **CITY:** CAMBRIDGE
- **STATE:** MA
- **ZIP:** 02142
- **BUSINESS PHONE:** (857) 400-9491

**MAIL ADDRESS:**
- **STREET 1:** 314 MAIN STREET, SUITE 04-200
- **CITY:** CAMBRIDGE
- **STATE:** MA
- **ZIP:** 02142
**FILED BY**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** ORBIMED ADVISORS LLC
- **CENTRAL INDEX KEY:** 0001055951
- **IRS NUMBER:** 133976876
- **STATE OF INCORPORATION:** DE

**FILING VALUES:**
- **FORM TYPE:** SC 13D/A

**BUSINESS ADDRESS:**
- **STREET 1:** 601 LEXINGTON AVENUE
- **STREET 2:** 54TH FLOOR
- **CITY:** NEW YORK
- **STATE:** NY
- **ZIP:** 10022
- **BUSINESS PHONE:** (212) 739-6400

**MAIL ADDRESS:**
- **STREET 1:** 601 LEXINGTON AVENUE
- **STREET 2:** 54TH FLOOR
- **CITY:** NEW YORK
- **STATE:** NY
- **ZIP:** 10022

**UNITED STATES**

**SECURITIES AND EXCHANGE COMMISSION**

**Washington, D.C. 20549**

**SCHEDULE 13D**

**(Amendment No. 2)\***

**Under the Securities Exchange Act of 1934**

---

| |
|:---|
| **Theseus Pharmaceuticals, Inc.** |
| &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; (Name of Issuer)<br>|
| **Common Stock** |
| &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; (Title of Class of Securities)<br>|
| **88369M101** |
| &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; (CUSIP Number)<br>|
| &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; **OrbiMed Advisors LLC**<br> **OrbiMed Capital GP VII LLC**<br> **OrbiMed Genesis GP LLC**<br>**601 Lexington Avenue, 54th Floor**<br> **New York, NY 10022**<br> **Telephone: (212) 739-6400**<br>|
| &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; (Name, Address and Telephone Number of Person Authorized to<br> Receive Notices and Communications)<br>|
| **March 9, 2023** |
| (Date of Event which Requires Filing of this Statement) |

---

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box. ☐

**Note:** Schedules filed in paper format shall include a signed original and five copies of the schedule, including all exhibits. See §240.13d-7(b) for other parties to whom copies are to be sent.

\* The remainder of this cover page shall be filled out for a Reporting Person's initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which would alter disclosures provided in a prior cover page.

The information required on the remainder of this cover page shall not be deemed to be "filed" for the purpose of Section 18 of the Securities Exchange Act of 1934 ("<u>Act</u>") or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

&nbsp;&nbsp;**CUSIP No. 88369M101**

---

| | | | | |
|:---|:---|:---|:---|:---|
| 1 | Names of Reporting Persons. <br> OrbiMed Advisors LLC | Names of Reporting Persons. <br> OrbiMed Advisors LLC | Names of Reporting Persons. <br> OrbiMed Advisors LLC | Names of Reporting Persons. <br> OrbiMed Advisors LLC |
| 2 | Check the Appropriate Box if a Member of a Group (See Instructions).<br> (a) □<br> (b) □ | Check the Appropriate Box if a Member of a Group (See Instructions).<br> (a) □<br> (b) □ | Check the Appropriate Box if a Member of a Group (See Instructions).<br> (a) □<br> (b) □ |  |
| 3 | &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; SEC Use Only  | &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; SEC Use Only  | &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; SEC Use Only  | &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; SEC Use Only  |
| 4 | Source of Funds (See Instructions)<br> AF | Source of Funds (See Instructions)<br> AF | Source of Funds (See Instructions)<br> AF | Source of Funds (See Instructions)<br> AF |
| 5 | Check if Disclosure of Legal Proceedings Is Required Pursuant to Items 2(d) or 2(e) | Check if Disclosure of Legal Proceedings Is Required Pursuant to Items 2(d) or 2(e) | Check if Disclosure of Legal Proceedings Is Required Pursuant to Items 2(d) or 2(e) | □ |
| 6 | Citizenship or Place of Organization <br> Delaware | Citizenship or Place of Organization <br> Delaware | Citizenship or Place of Organization <br> Delaware | Citizenship or Place of Organization <br> Delaware |
| NUMBER OF<br> SHARES<br> BENEFICIALLY<br> OWNED BY<br> EACH<br> REPORTING<br> PERSON<br> WITH | NUMBER OF<br> SHARES<br> BENEFICIALLY<br> OWNED BY<br> EACH<br> REPORTING<br> PERSON<br> WITH | 7 | Sole Voting Power <br> 0 | Sole Voting Power <br> 0 |
| NUMBER OF<br> SHARES<br> BENEFICIALLY<br> OWNED BY<br> EACH<br> REPORTING<br> PERSON<br> WITH | NUMBER OF<br> SHARES<br> BENEFICIALLY<br> OWNED BY<br> EACH<br> REPORTING<br> PERSON<br> WITH | 8 | Shared Voting Power <br> 17,233,668 | Shared Voting Power <br> 17,233,668 |
| NUMBER OF<br> SHARES<br> BENEFICIALLY<br> OWNED BY<br> EACH<br> REPORTING<br> PERSON<br> WITH | NUMBER OF<br> SHARES<br> BENEFICIALLY<br> OWNED BY<br> EACH<br> REPORTING<br> PERSON<br> WITH | 9 | Sole Dispositive Power <br> 0 | Sole Dispositive Power <br> 0 |
| NUMBER OF<br> SHARES<br> BENEFICIALLY<br> OWNED BY<br> EACH<br> REPORTING<br> PERSON<br> WITH | NUMBER OF<br> SHARES<br> BENEFICIALLY<br> OWNED BY<br> EACH<br> REPORTING<br> PERSON<br> WITH | 10 | Shared Dispositive Power <br> 17,233,668 | Shared Dispositive Power <br> 17,233,668 |
| 11 | Aggregate Amount Beneficially Owned by Each Reporting Person <br> 17,233,668 | Aggregate Amount Beneficially Owned by Each Reporting Person <br> 17,233,668 | Aggregate Amount Beneficially Owned by Each Reporting Person <br> 17,233,668 | Aggregate Amount Beneficially Owned by Each Reporting Person <br> 17,233,668 |
| 12 | Check if the Aggregate Amount in Row (11) Excludes Certain Shares (See Instructions) | Check if the Aggregate Amount in Row (11) Excludes Certain Shares (See Instructions) | Check if the Aggregate Amount in Row (11) Excludes Certain Shares (See Instructions) | □ |
| 13 | Percent of Class Represented by Amount in Row (11) <br> 39.6%\* | Percent of Class Represented by Amount in Row (11) <br> 39.6%\* | Percent of Class Represented by Amount in Row (11) <br> 39.6%\* | Percent of Class Represented by Amount in Row (11) <br> 39.6%\* |
| 14 | Type of Reporting Person (See Instructions) <br> IA | Type of Reporting Person (See Instructions) <br> IA | Type of Reporting Person (See Instructions) <br> IA | Type of Reporting Person (See Instructions) <br> IA |

---

\* This percentage is calculated based upon 43,561,124 shares of common stock, par value $0.0001 per share, outstanding of Theseus Pharmaceuticals, Inc. (the "<u>Issuer</u>"), as set forth in the Issuer's Annual Report on Form 10-K for the year ending December 31, 2022 filed with the Securities and Exchange Commission on March 9, 2023.

&nbsp;&nbsp;**CUSIP No. 88369M101**

---

| | | | | |
|:---|:---|:---|:---|:---|
| 1 | Names of Reporting Persons. <br> OrbiMed Capital GP VII LLC | Names of Reporting Persons. <br> OrbiMed Capital GP VII LLC | Names of Reporting Persons. <br> OrbiMed Capital GP VII LLC | Names of Reporting Persons. <br> OrbiMed Capital GP VII LLC |
| 2 | Check the Appropriate Box if a Member of a Group (See Instructions).<br> (a) □<br> (b) □ | Check the Appropriate Box if a Member of a Group (See Instructions).<br> (a) □<br> (b) □ | Check the Appropriate Box if a Member of a Group (See Instructions).<br> (a) □<br> (b) □ |  |
| 3 | SEC Use Only | SEC Use Only | SEC Use Only | SEC Use Only |
| 4 | Source of Funds (See Instructions) <br> AF | Source of Funds (See Instructions) <br> AF | Source of Funds (See Instructions) <br> AF | Source of Funds (See Instructions) <br> AF |
| 5 | Check if Disclosure of Legal Proceedings Is Required Pursuant to Items 2(d) or 2(e) | Check if Disclosure of Legal Proceedings Is Required Pursuant to Items 2(d) or 2(e) | Check if Disclosure of Legal Proceedings Is Required Pursuant to Items 2(d) or 2(e) | □ |
| 6 | Citizenship or Place of Organization <br> Delaware | Citizenship or Place of Organization <br> Delaware | Citizenship or Place of Organization <br> Delaware | Citizenship or Place of Organization <br> Delaware |
| NUMBER OF<br> SHARES<br> BENEFICIALLY<br> OWNED BY<br> EACH<br> REPORTING<br> PERSON<br> WITH | NUMBER OF<br> SHARES<br> BENEFICIALLY<br> OWNED BY<br> EACH<br> REPORTING<br> PERSON<br> WITH | 7 | Sole Voting Power <br> 0 | Sole Voting Power <br> 0 |
| NUMBER OF<br> SHARES<br> BENEFICIALLY<br> OWNED BY<br> EACH<br> REPORTING<br> PERSON<br> WITH | NUMBER OF<br> SHARES<br> BENEFICIALLY<br> OWNED BY<br> EACH<br> REPORTING<br> PERSON<br> WITH | 8 | Shared Voting Power <br> 16,734,518 | Shared Voting Power <br> 16,734,518 |
| NUMBER OF<br> SHARES<br> BENEFICIALLY<br> OWNED BY<br> EACH<br> REPORTING<br> PERSON<br> WITH | NUMBER OF<br> SHARES<br> BENEFICIALLY<br> OWNED BY<br> EACH<br> REPORTING<br> PERSON<br> WITH | 9 | Sole Dispositive Power <br> 0 | Sole Dispositive Power <br> 0 |
| NUMBER OF<br> SHARES<br> BENEFICIALLY<br> OWNED BY<br> EACH<br> REPORTING<br> PERSON<br> WITH | NUMBER OF<br> SHARES<br> BENEFICIALLY<br> OWNED BY<br> EACH<br> REPORTING<br> PERSON<br> WITH | 10 | Shared Dispositive Power <br> 16,734,518 | Shared Dispositive Power <br> 16,734,518 |
| 11 | Aggregate Amount Beneficially Owned by Each Reporting Person <br> 16,734,518 | Aggregate Amount Beneficially Owned by Each Reporting Person <br> 16,734,518 | Aggregate Amount Beneficially Owned by Each Reporting Person <br> 16,734,518 | Aggregate Amount Beneficially Owned by Each Reporting Person <br> 16,734,518 |
| 12 | Check if the Aggregate Amount in Row (11) Excludes Certain Shares (See Instructions) | Check if the Aggregate Amount in Row (11) Excludes Certain Shares (See Instructions) | Check if the Aggregate Amount in Row (11) Excludes Certain Shares (See Instructions) | □ |
| 13 | Percent of Class Represented by Amount in Row (11) <br> 38.4%\* | Percent of Class Represented by Amount in Row (11) <br> 38.4%\* | Percent of Class Represented by Amount in Row (11) <br> 38.4%\* | Percent of Class Represented by Amount in Row (11) <br> 38.4%\* |
| 14 | Type of Reporting Person (See Instructions) <br> OO | Type of Reporting Person (See Instructions) <br> OO | Type of Reporting Person (See Instructions) <br> OO | Type of Reporting Person (See Instructions) <br> OO |

---

\* This percentage is calculated based upon 43,561,124 shares of common stock, par value $0.0001 per share, outstanding of Theseus Pharmaceuticals, Inc. (the "<u>Issuer</u>"), as set forth in the Issuer's Annual Report on Form 10-K for the year ending December 31, 2022 filed with the Securities and Exchange Commission on March 9, 2023.

---

| | | | |
|:---|:---|:---|:---|
| &nbsp;&nbsp;**CUSIP No. 88369M101** | &nbsp;&nbsp;**CUSIP No. 88369M101** | &nbsp;&nbsp;**CUSIP No. 88369M101** |  |
| 1 | Names of Reporting Persons. <br> OrbiMed Genesis GP LLC | Names of Reporting Persons. <br> OrbiMed Genesis GP LLC | Names of Reporting Persons. <br> OrbiMed Genesis GP LLC |
| 2 | Check the Appropriate Box if a Member of a Group (See Instructions).<br> (a) □<br> (b) □ | Check the Appropriate Box if a Member of a Group (See Instructions).<br> (a) □<br> (b) □ |  |
| 3 | SEC Use Only | SEC Use Only | SEC Use Only |
| 4 | Source of Funds (See Instructions) <br> AF | Source of Funds (See Instructions) <br> AF | Source of Funds (See Instructions) <br> AF |
| 5 | Check if Disclosure of Legal Proceedings Is Required Pursuant to Items 2(d) or 2(e) | Check if Disclosure of Legal Proceedings Is Required Pursuant to Items 2(d) or 2(e) | □ |
| 6 | Citizenship or Place of Organization <br> Cayman Islands | Citizenship or Place of Organization <br> Cayman Islands | Citizenship or Place of Organization <br> Cayman Islands |
| NUMBER OF<br> SHARES<br> BENEFICIALLY<br> OWNED BY<br> EACH<br> REPORTING<br> PERSON<br> WITH | 7 | Sole Voting Power <br> 0 | Sole Voting Power <br> 0 |
| NUMBER OF<br> SHARES<br> BENEFICIALLY<br> OWNED BY<br> EACH<br> REPORTING<br> PERSON<br> WITH | 8 | Shared Voting Power <br> 499,150 | Shared Voting Power <br> 499,150 |
| NUMBER OF<br> SHARES<br> BENEFICIALLY<br> OWNED BY<br> EACH<br> REPORTING<br> PERSON<br> WITH | 9 | Sole Dispositive Power <br> 0 | Sole Dispositive Power <br> 0 |
| NUMBER OF<br> SHARES<br> BENEFICIALLY<br> OWNED BY<br> EACH<br> REPORTING<br> PERSON<br> WITH | 10 | Shared Dispositive Power <br> 499,150 | Shared Dispositive Power <br> 499,150 |
| 11 | Aggregate Amount Beneficially Owned by Each Reporting Person <br> 499,150 | Aggregate Amount Beneficially Owned by Each Reporting Person <br> 499,150 | Aggregate Amount Beneficially Owned by Each Reporting Person <br> 499,150 |
| 12 | Check if the Aggregate Amount in Row (11) Excludes Certain Shares (See Instructions) | Check if the Aggregate Amount in Row (11) Excludes Certain Shares (See Instructions) | □ |
| 13 | Percent of Class Represented by Amount in Row (11) <br> 1.2%\* | Percent of Class Represented by Amount in Row (11) <br> 1.2%\* | Percent of Class Represented by Amount in Row (11) <br> 1.2%\* |
| 14 | Type of Reporting Person (See Instructions) <br> IA | Type of Reporting Person (See Instructions) <br> IA | Type of Reporting Person (See Instructions) <br> IA |

---

\* This percentage is calculated based upon 43,561,124 shares of common stock, par value $0.0001 per share, outstanding of Theseus Pharmaceuticals, Inc. (the "<u>Issuer</u>"), as set forth in the Issuer's Annual Report on Form 10-K for the year ending December 31, 2022 filed with the Securities and Exchange Commission on March 9, 2023.

**Item 1. Security and Issuer**

This Amendment No. 2 ("<u>Amendment No. 2</u>") to Schedule 13D supplements and amends the Statement on Schedule 13D of OrbiMed Advisors LLC, OrbiMed Capital GP VII LLC, and OrbiMed Genesis GP LLC (the "<u>Statement</u>") originally filed with the Securities and Exchange Commission (the "<u>SEC</u>") on October 19, 2021, as amended by Amendment No. 1 filed with the SEC on November 18, 2021. This Statement relates to the common stock, par value $0.0001 per share (the "<u>Shares</u>"), of Theseus Pharmaceuticals, Inc., a corporation organized under the laws of Delaware (the "<u>Issuer</u>"), with its principal executive offices located at 314 Main Street, Cambridge, Massachusetts 02142. The Shares are listed on the NASDAQ Global Select Market under the ticker symbol "THRX". Information given in response to each item shall be deemed incorporated by reference in all other items, as applicable.

The Reporting Persons (as defined below) are filing this Amendment No. 2 to report a decrease in the percentage of the total number of outstanding Shares of the Issuer beneficially owned by the Reporting Persons due to an increase in the total number of outstanding Shares of the Issuer as reported on the Issuer's Annual Report on Form 10-K for the year ended December 31, 2022.

**Item 2. Identity and Background**

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(a) This Schedule 13D is being filed by OrbiMed Advisors LLC ("<u>OrbiMed Advisors</u>"), OrbiMed Capital GP VII LLC, ("<u>GP VII</u>"), and OrbiMed Genesis GP LLC ("<u>Genesis GP</u>") (collectively, the "<u>Reporting Persons</u>").

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(b) — (c), (f) GP VII, a limited liability company organized under the laws of Delaware, is the general partner of a limited partnership, as more particularly described in Item 6 below. GP VII has its principal offices at 601 Lexington Avenue, 54th Floor, New York, New York 10022.

Genesis GP, a limited liability company organized under the laws of Delaware, is the general partner of a limited partnership, as more particularly described in Item 6 below. Genesis GP has its principal offices at 601 Lexington Avenue, 54th Floor, New York, New York 10022.

OrbiMed Advisors, a limited liability company organized under the laws of Delaware and a registered investment adviser under the Investment Advisers Act of 1940, as amended, is the managing member of GP VII and Genesis GP, as more particularly described in Item 6 below. OrbiMed Advisors has its principal offices at 601 Lexington Avenue, 54th Floor, New York, New York 10022.

The directors and executive officers of OrbiMed Advisors, GP VII, and Genesis GP are set forth on Schedules I, II, and III, respectively, attached hereto. Schedules I, II, and III set forth the following information with respect to each such person:

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(i) name;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(ii) business address;

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(iii) present principal occupation of employment and the name, principal business and address of any corporation or other organization in which such employment is conducted; and

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(iv) citizenship.

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(d) — (e) During the last five years, neither the Reporting Persons nor any Person named in Schedules I through III has been (i) convicted in a criminal proceeding (excluding traffic violations or similar misdemeanors) or (ii) a party to a civil proceeding of a judicial or administrative body of competent jurisdiction and as a result of such proceeding was or is subject to a judgment, decree or final order enjoining future violations of, or prohibiting or mandating activities subject to, federal or state securities laws or finding any violation with respect to such laws.

**Item 3. Source and Amount of Funds or Other Consideration**

Not applicable.

**Item 4. Purpose of Transaction**

The Shares acquired by the Reporting Persons were acquired for the purpose of making an investment in the Issuer and not with the intention of acquiring control of the Issuer's business on behalf of the Reporting Persons' respective advisory clients.

The Reporting Persons from time to time intend to review their investment in the Issuer on the basis of various factors, including the Issuer's business, financial condition, results of operations and prospects, general economic and industry conditions, the securities markets in general and those for the Issuer's Shares in particular, as well as other developments and other investment opportunities. Based upon such review, the Reporting Persons will take such actions in the future as the Reporting Persons may deem appropriate in light of the circumstances existing from time to time. If the Reporting Persons believe that further investment in the Issuer is attractive, whether because of the market price of Shares or otherwise, they may acquire Shares or other securities of the Issuer either in the open market or in privately negotiated transactions. Similarly, depending on market and other factors, the Reporting Persons may determine to dispose of some or all of the Shares currently owned by the Reporting Persons or otherwise acquired by the Reporting Persons either in the open market or in privately negotiated transactions.

Except as set forth in this Schedule 13D, the Reporting Persons have not formulated any plans or proposals which relate to or would result in: (a) the acquisition by any person of additional securities of the Issuer or the disposition of securities of the Issuer, (b) an extraordinary corporate transaction, such as a merger, reorganization or liquidation, involving the Issuer or any of its subsidiaries, (c) a sale or transfer of a material amount of the assets of the Issuer or any of its subsidiaries, (d) any change in the present Board of Directors or management of the Issuer, including any plans or proposals to change the number or term of directors or to fill any existing vacancies on the board, (e) any material change in the Issuer's capitalization or dividend policy of the Issuer, (f) any other material change in the Issuer's business or corporate structure, (g) any change in the Issuer's charter or bylaws or other instrument corresponding thereto or other action which may impede the acquisition of control of the Issuer by any person, (h) causing a class of the Issuer's securities to be deregistered or delisted from a national securities exchange or to cease to be authorized to be quoted in an inter-dealer quotation system of a registered national securities association, (i) a class of equity securities of the Issuer becoming eligible for termination of registration pursuant to Section 12(g)(4) of the Act or (j) any action similar to any of those enumerated above.

**Item 5. Interest in Securities of the Issuer**

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(a) — (b) The following disclosure is based upon 43,561,124 Shares outstanding of Issuer, as set forth in the Issuer's Annual Report on Form 10-K for the year ending December 31, 2022 filed with the SEC on March 9, 2023.

As of the date of this filing, OrbiMed Private Investments VII, LP ("<u>OPI VII</u>"), a limited partnership organized under the laws of Delaware, holds 16,734,518 Shares, constituting approximately 38.4% of the issued and outstanding Shares. GP VII is the general partner of OPI VII, pursuant to the terms of the limited partnership agreement of OPI VII, and OrbiMed Advisors is the managing member of GP VII, pursuant to the terms of the limited liability company agreement of GP VII. As a result, OrbiMed Advisors and GP VII share power to direct the vote and disposition of the Shares held by OPI VII and may be deemed directly or indirectly, including by reason of their mutual affiliation, to be the beneficial owners of the Shares held by OPI VII. OrbiMed Advisors exercises this investment and voting power through a management committee comprised of Carl L. Gordon, Sven H. Borho, and W. Carter Neild, each of whom disclaims beneficial ownership of the Shares held by OPI VII.

In addition, OrbiMed Advisors and GP VII, pursuant to their authority under the limited partnership agreement of OPI VII, caused OPI VII to enter into the agreements referred to in Item 6 below.

As of the date of this filing, OrbiMed Genesis Master Fund, L.P. ("<u>Genesis</u>"), a limited partnership organized under the laws of the Cayman Islands, holds 499,150 Shares constituting approximately 1.2% of the issued and outstanding Shares. Genesis GP is the general partner of Genesis, pursuant to the terms of the limited partnership agreement of Genesis, and OrbiMed Advisors is the managing member of Genesis GP, pursuant to the terms of the limited liability company agreement of Genesis GP. As a result, OrbiMed Advisors and Genesis GP share power to direct the vote and disposition of the Shares held by Genesis and may be deemed, directly or indirectly, including by reason of their mutual affiliation, to be the beneficial owners of the Shares held by Genesis. OrbiMed Advisors exercises this investment and voting power through a management committee comprised of Carl L. Gordon, Sven H. Borho, and W. Carter Neild, each of whom disclaims beneficial ownership of the Shares held by Genesis.

In addition, OrbiMed Advisors and Genesis GP, pursuant to their authority under the limited partnership agreement of Genesis, caused Genesis to enter into the agreements referred to in Item 6 below.

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(c) The Reporting Persons have not effected any transactions during the past sixty (60) days in any Shares.

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(d) Not applicable.

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(e) Not applicable.

**Item 6. Contracts, Arrangements, Understandings or Relationships with Respect to Securities of the Issuer**

In addition to the relationships between the Reporting Persons described in Items 2 and 5 above, GP VII is the general partner of OPI VII, pursuant to the terms of the limited partnership agreement of OPI VII. Pursuant to this agreement and relationship, GP VII has discretionary investment management authority with respect to the assets of OPI VII. Such authority includes the power to vote and otherwise dispose of securities held by OPI VII. The number of outstanding Shares of the Issuer attributable to OPI VII is 16,734,518 Shares. GP VII, pursuant to its authority under the limited partnership agreement of OPI VII, may be considered to hold indirectly 16,734,518 Shares.

In addition to the relationships between the Reporting Persons described in Items 2 and 5 above, Genesis GP is the general partner of Genesis, pursuant to the terms of the limited partnership agreement of Genesis. Pursuant to this agreement and relationship, Genesis GP has discretionary investment management authority with respect to the assets of Genesis. Such authority includes the power to vote and otherwise dispose of securities held by Genesis. The number of outstanding Shares of the Issuer attributable to Genesis is 499,150 Shares. Genesis GP, pursuant to its authority under the limited partnership agreement of Genesis, may be considered to hold indirectly 499,150 Shares.

In addition to the relationships between the Reporting Persons described in Items 2 and 5 above, OrbiMed Advisors is the managing member of GP VII and Genesis GP, pursuant to the terms of the limited liability company agreements of GP VII and Genesis GP. Pursuant to these agreements and relationships, OrbiMed Advisors and GP VII have discretionary investment management authority with respect to the assets of OPI VII. OrbiMed Advisors and Genesis GP have discretionary investment management authority with respect to the assets of Genesis. Such authority includes the power of GP VII to vote and otherwise dispose of securities held by OPI VII and the power of Genesis GP to vote and otherwise dispose of the securities held by Genesis. The number of outstanding Shares attributable to OPI VII is 16,734,518 Shares and the number of Shares attributed to Genesis is 499,150 Shares. OrbiMed Advisors, pursuant to its authority under the terms of the limited liability company agreements of GP VII and Genesis GP, may also be considered to hold indirectly 17,233,668 Shares.

Carl Gordon ("<u>Gordon</u>"), a member of OrbiMed Advisors, is a member of the Board of Directors of the Issuer and, accordingly, OrbiMed Advisors and GP VII may have the ability to affect and influence control of the Issuer. From time to time, Gordon may receive stock options or other awards of equity-based compensation pursuant to the Issuer's compensation arrangements for non-employee directors. Pursuant to an agreement with OrbiMed Advisors and GP VII, Gordon is obligated to transfer any securities issued under any such stock options or other awards, or the economic benefit thereof, to OrbiMed Advisors and GP VII, which will in turn ensure that such securities or economic benefits are provided to OPI VII.

 

***Investors' Rights Agreement***

In addition, OPI VII, Genesis, and certain other stockholders of the Issuer entered into an Amended and Restated Investors' Rights Agreement with the Issuer (the "<u>Investors' Rights Agreement</u>"), dated as of January 22, 2021. Pursuant to the Investors' Rights Agreement and subject to the terms and conditions therein, the parties agreed that:

 

*Demand Registration Rights*

At any time beginning six months following the date of the effective date of the registration statement of the Issuer's initial public offering, a majority of the holders of the registrable securities then outstanding of the Issuer may make a written request that the Issuer register some or all of their registrable securities, subject to certain specified conditions and exceptions, including that the aggregated gross offering price of such offering must exceed $15 million. The Issuer is required to use commercially reasonable efforts to effect the registration and will pay all registration expenses, other than underwriting discounts and commissions, related to any demand registration. The Issuer is not obligated to effect more than two of these registrations.

 

*Piggyback Registration Rights*

 

Whenever the Issuer proposes to file a registration statement under the Securities Act, other than with respect to certain excluded registrations, OPI VII and Genesis will be entitled to notice of the registration and have the right, subject to limitations that the underwriters may impose on the number of Shares included in the registration, to include the Shares held by them in the registration.

*Form S-3 Registration Rights*

 

At any time after the Issuer is qualified to file a registration statement on Form S-3 under the Securities Act, and subject to limitations and conditions specified in the Investors' Rights Agreement, holders of the registrable securities then outstanding may make a written request that the Issuer prepare and file a registration statement on Form S-3 covering their Shares, so long as the aggregate price to the public equal or exceeds $10 million. The Issuer is not obligated to effect more than two of these Form S-3 registrations in any 12-month period.

The foregoing description of the Investors' Rights Agreement does not purport to be complete and is qualified in its entirety by reference to the full text of the Investors' Rights Agreement, which is filed as Exhibit 2 and incorporated herein by reference.

**Item 7. Material to Be Filed as Exhibits**

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| | |
|:---|:---|
| &nbsp;&nbsp;**Exhibit** | &nbsp;&nbsp;**Description** |
| &nbsp;&nbsp;1. | &nbsp;&nbsp;Joint Filing Agreement among OrbiMed Advisors LLC, OrbiMed Capital GP VII LLC, and OrbiMed Genesis GP LLC. |
| &nbsp;&nbsp;2. | &nbsp;&nbsp;Amended and Restated Investors' Rights Agreement by and among the Issuer and each of the signatories thereto, dated as of January 22, 2021 (incorporated by reference to Exhibit 4.2 to the Issuer's Registration Statement on Form S-1 (SEC 333-259549), filed with the SEC on September 15, 2021). |

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**Signature**

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Dated: March 14, 2023

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| | |
|:---|:---|
| ORBIMED ADVISORS LLC | ORBIMED ADVISORS LLC |
| By: | <u>/s/ Carl L. Gordon</u> |
|  | Name: Carl L. Gordon |
|  | Title: Member |
| ORBIMED CAPITAL GP VII LLC | ORBIMED CAPITAL GP VII LLC |
| By: | ORBIMED ADVISORS LLC, its managing member |
| By: | <u>/s/ Carl L. Gordon</u> |
|  | Name: Carl L. Gordon |
|  | Title: Member of OrbiMed Advisors LLC |
| ORBIMED GENESIS GP LLC | ORBIMED GENESIS GP LLC |
| By: | ORBIMED ADVISORS LLC, its managing member |
| By: | <u>s/ Carl L. Gordon</u> |
|  | Name: Carl L. Gordon |
|  | Title: Member of OrbiMed Advisors LLC |

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**SCHEDULE I**

The names and present principal occupations of each of the executive officers and directors of OrbiMed Advisors LLC are set forth below. Unless otherwise noted, each of these persons is a United States citizen and has a business address of 601 Lexington Avenue, 54th Floor, New York, NY 10022.

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| | | |
|:---|:---|:---|
| <u>Name</u> | <u>Position with Reporting Person</u> | <u>Principal Occupation</u> |
| Carl L. Gordon | Member | Member<br> OrbiMed Advisors LLC |
| Sven H. Borho<br> German and Swedish Citizen | Member | Member<br> OrbiMed Advisors LLC |
| W. Carter Neild | Member | Member<br> OrbiMed Advisors LLC |
| Geoffrey C. Hsu | Member | Member<br> OrbiMed Advisors LLC |
| C. Scotland Stevens | Member | Member<br> OrbiMed Advisors LLC |
| David P. Bonita | Member | Member<br> OrbiMed Advisors LLC |
| Peter A. Thompson | Member | Member<br> OrbiMed Advisors LLC |
| Matthew S. Rizzo | Member | Member<br> OrbiMed Advisors LLC |
| Trey Block | Chief Financial Officer<br>| Chief Financial Officer<br> OrbiMed Advisors LLC |

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**SCHEDULE II**

The business and operations of OrbiMed Capital GP VII LLC are managed by the executive officers and directors of its managing member, OrbiMed Advisors LLC, set forth on Schedule I attached.

**SCHEDULE III**

The business and operations of OrbiMed Genesis GP LLC are managed by the executive officers and directors of its managing member, OrbiMed Advisors LLC, set forth on Schedule I attached.

**EXHIBIT INDEX**

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| | |
|:---|:---|
| &nbsp;&nbsp;**Exhibit** | &nbsp;&nbsp;**Description** |
| &nbsp;&nbsp;1. | &nbsp;&nbsp;Joint Filing Agreement among OrbiMed Advisors LLC, OrbiMed Capital GP VII LLC, and OrbiMed Genesis GP LLC. |
| &nbsp;&nbsp;2. | &nbsp;&nbsp;Amended and Restated Investors' Rights Agreement by and among the Issuer and each of the signatories thereto, dated as of January 22, 2021 (incorporated by reference to Exhibit 4.2 to the Issuer's Registration Statement on Form S-1 (SEC 333-259549), filed with the SEC on September 15, 2021). |

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## Exhibit 99.1

**<u>Exhibit 1</u>**

JOINT FILING AGREEMENT

The undersigned hereby agree that the Statement on Schedule 13D, dated March 9, 2023, with respect to the common stock of Theseus Pharmaceuticals, Inc. is filed on behalf of each of us pursuant to and in accordance with the provisions of Rule 13d-1(k) under the Securities Exchange Act of 1934, as amended. Each of the undersigned agrees to be responsible for the timely filing of this Statement, and for the completeness and accuracy of the information concerning itself contained therein. This Agreement may be executed in any number of counterparts, all of which taken together shall constitute one and the same instrument.

IN WITNESS WHEREOF, the undersigned have executed this Agreement as of the 14<sup>th</sup> day of March 2023.

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| | |
|:---|:---|
| ORBIMED ADVISORS LLC | ORBIMED ADVISORS LLC |
| By: | <u>/s/ Carl L. Gordon</u> |
|  | Name: Carl L. Gordon |
|  | Title: Member |
| ORBIMED CAPITAL GP VII LLC | ORBIMED CAPITAL GP VII LLC |
| By: | ORBIMED ADVISORS LLC, its managing member |
| By: | <u>/s/ Carl L. Gordon</u> |
|  | Name: Carl L. Gordon |
|  | Title: Member of OrbiMed Advisors LLC |
| ORBIMED GENESIS GP LLC | ORBIMED GENESIS GP LLC |
| By: | ORBIMED ADVISORS LLC, its managing member |
| By: | <u>s/ Carl L. Gordon</u> |
|  | Name: Carl L. Gordon |
|  | Title: Member of OrbiMed Advisors LLC |

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