FORM 3
        
UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549
INITIAL STATEMENT OF BENEFICIAL OWNERSHIP OF SECURITIES

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Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934 or Section 30(h) of the Investment Company Act of 1940
                      
1. Name and Address of Reporting Person * TAKEDA PHARMACEUTICAL CO LTD 2. Date of Event Requiring Statement (MM/DD/YYYY)
10/6/2021 

3. Issuer Name and Ticker or Trading Symbol Theseus Pharmaceuticals, Inc. [THRX]
(Last)       (First)       (Middle)
1-1, NIHONBASHI-HONCHO 2-CHOME
4. Relationship of Reporting Person(s) to Issuer (Check all applicable)_____ Director                          ___X___ 10% Owner
_____ Officer (give title below)        _____ Other (specify below)
(Street)
CHUO-KU, TOKYO, M0 103-8668      
(City)             (State)             (Zip)
5. If Amendment, Date Original Filed(MM/DD/YYYY)
 

6. Individual or Joint/Group Filing(Check Applicable Line)___ Form filed by One Reporting Person
_X_ Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Beneficially Owned
1.Title of Security
(Instr. 4)
2. Amount of Securities Beneficially Owned
(Instr. 4)
3. Ownership Form: Direct (D) or Indirect (I)
(Instr. 5)
4. Nature of Indirect Beneficial Ownership
(Instr. 5)

Table II - Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivate Security
(Instr. 4)
2. Date Exercisable and Expiration Date
(MM/DD/YYYY)
3. Title and Amount of Securities Underlying Derivative Security
(Instr. 4)
4. Conversion or Exercise Price of Derivative Security 5. Ownership Form of Derivative Security: Direct (D) or Indirect (I)
(Instr. 5)
6. Nature of Indirect Beneficial Ownership
(Instr. 5)
Date Exercisable Expiration Date Title Amount or Number of Shares
Series A Preferred Stock   (1)  (1) Common Stock  1615427.0   (1) I  See explanation (2)(3)

Explanation of Responses:
(1)  These shares of the Issuers Series A Preferred Stock are expected to convert on a one-for-one basis into the number of shares of the Issuers common stock, par value $0.0001 per share (Common Stock), shown in Column 3 immediately upon the closing of the Issuers initial public offering without payment of additional consideration. The Series A Preferred Stock has no expiration date.
(2)  This statement is being filed jointly by Takeda Pharmaceutical Company Limited and ARIAD Pharmaceuticals, Inc.
(3)  Takeda Pharmaceutical Company Limiteds beneficial ownership of the reported securities is comprised of 1,615,427 shares of Series A Preferred Stock held by ARIAD Pharmaceuticals, Inc. ARIAD Pharmaceuticals, Inc., is a direct, wholly owned subsidiary of Takeda Pharmaceuticals U.S.A. Inc., which is a direct subsidiary of Takeda Pharmaceutical Company Limited (72.70%) and Takeda Pharmaceuticals International AG (27.3%). Takeda Pharmaceuticals International AG is a direct, wholly owned subsidiary of Takeda Pharmaceutical Company Limited.

Reporting Owners
Reporting Owner Name / Address
Relationships
Director 10% Owner Officer Other
TAKEDA PHARMACEUTICAL CO LTD
1-1, NIHONBASHI-HONCHO 2-CHOME
CHUO-KU, TOKYO, M0 103-8668

X

ARIAD PHARMACEUTICALS INC
40 LANDSDOWNE STREET
CAMBRIDGE, MA 02139

X


Signatures
/s/ Yoshihiro Nakagawa, Corporate Officer, Global General Counsel of Takeda Pharmaceutical Company Limited 10/6/2021
**Signature of Reporting Person Date
/s/ Paul Sundberg, Attorney-in-Fact for ARIAD Pharmaceuticals, Inc. 10/6/2021
**Signature of Reporting Person Date
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