Statement of Changes in Beneficial Ownership (Form 4)

FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b). Check this box to indicate that a transaction was made pursuant to a contract, instruction or written plan that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP OF SECURITIES Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934 or Section 30(h) of the Investment Company Act of 1940

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(Print or Type Responses)

1. Name and Address of Reporting Person * MPM BIOVENTURES 2018, L.P. 2. Issuer Name and Ticker or Trading Symbol Aktis Oncology, Inc. [AKTS] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director __X__ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) C/O MPM BIOIMPACT LLC, 399 BOYLSTON STREET, SUITE 1100 3. Date of Earliest Transaction (Month/Day/Year) 01/12/2026 (Street) BOSTON, MA 02116 4. If Amendment, Date Original Filed (Month/Day/Year) 6. Individual or Joint/Group Filing (Check Applicable Line) ___ Form filed by One Reporting Person _X_ Form filed by More than One Reporting Person (City) (State) (Zip) Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned

1.Title of Security (Instr. 3) 2. Transaction Date (Month/Day/Year) 2A. Deemed Execution Date, if any (Month/Day/Year) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Common Stock 01/12/2026 C 1,314,262(1) A (2) 1,655,971 I See Footnote(3)(4) Common Stock 01/12/2026 C 5,914,197(5) A (2) 7,570,168 I See Footnote(3)(6) Common Stock 01/12/2026 C 1,577,119(7) A (2) 9,147,287 I See Footnote(3)(8) Common Stock 01/12/2026 P 1,112,777(9) A $18 10,260,064 I See Footnote(3)(10)

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Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned
(e.g., puts, calls, warrants, options, convertible securities)

1. Title of Derivative Security (Instr. 3)

2. Conversion or Exercise Price of Derivative Security

3. Transaction Date (Month/Day/Year)

3A. Deemed Execution Date, if any (Month/Day/Year)

4. Transaction Code (Instr. 8)

5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5)

6. Date Exercisable and Expiration Date (Month/Day/Year)

7. Title and Amount of Underlying Securities (Instr. 3 and 4)

8. Price of Derivative Security (Instr. 5)

9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)

10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4)

11. Nature of Indirect Beneficial Ownership (Instr. 4)

Code

V

(A)

(D)

Date Exercisable

Expiration Date

Title

Amount or Number of Shares

Series Seed Redeemable Convertible Preferred Stock

(2)

01/12/2026

C

5,000,000

(2)

(2)

Common Stock

1,314,262

$ 0 (2)

0

I

See Footnote(1)(3)

Series A Redeemable Convertible Preferred Stock

(2)

01/12/2026

C

22,500,000

(2)

(2)

Common Stock

5,914,197

$ 0 (2)

0

I

See Footnote(3)(5)

Series B Redeemable Convertible Preferred Stock

(2)

01/12/2026

C

6,000,000

(2)

(2)

Common Stock

1,577,119

$ 0 (2)

0

I

See Footnote(3)(7)

Reporting Owners

Reporting Owner Name / Address	Relationships
	Director	10% Owner	Officer	Other
MPM BIOVENTURES 2018, L.P. C/O MPM BIOIMPACT LLC 399 BOYLSTON STREET, SUITE 1100 BOSTON, MA 02116		X
EVNIN LUKE C/O MPM BIOIMPACT LLC 399 BOYLSTON STREET, SUITE 1100 BOSTON, MA 02116		X
MPM BIOVENTURES 2018 (B), L.P. C/O MPM BIOIMPACT LLC 399 BOYLSTON STREET, SUITE 1100 BOSTON, MA 02116		X
MPM BioVentures 2018 LLC C/O MPM BIOIMPACT LLC 399 BOYLSTON STREET, SUITE 1100 BOSTON, MA 02116		X
MPM BioVentures 2018 GP LLC C/O MPM BIOIMPACT LLC 399 BOYLSTON STREET, SUITE 1100 BOSTON, MA 02116		X
MPM ASSET MANAGEMENT INVESTORS BV2018 LLC C/O MPM BIOIMPACT LLC 399 BOYLSTON STREET, SUITE 1100 BOSTON, MA 02116		X
MPM ONCOLOGY INNOVATIONS FUND LP C/O MPM BIOIMPACT LLC 399 BOYLSTON STREET, SUITE 1100 BOSTON, MA 02116		X
MPM Oncology Innovations Fund GP LLC C/O MPM BIOIMPACT LLC 399 BOYLSTON STREET, SUITE 1100 BOSTON, MA 02116		X

Signatures

/s/ Luke Evnin		01/14/2026
**Signature of Reporting Person		Date
/s/ Ansbert Gadicke, managing director of MPM BioVentures 2018 LLC, the managing member of MPM BioVentures 2018 GP LLC, the GP of MPM BioVentures 2018 (B), L		01/14/2026
**Signature of Reporting Person		Date
/s/ Ansbert Gadicke, managing director of MPM BioVentures 2018 LLC		01/14/2026
**Signature of Reporting Person		Date
/s/ Ansbert Gadicke, managing director of MPM BioVentures 2018 LLC, the managing member of MPM BioVentures 2018 GP LLC		01/14/2026
**Signature of Reporting Person		Date
/s/ Ansbert Gadicke, managing director of MPM BioVentures 2018 LLC, the managing member of MPM BioVentures 2018 GP LLC, the GP of MPM BioVentures 2018, L.P.		01/14/2026
**Signature of Reporting Person		Date
/s/ Ansbert Gadicke, managing director of MPM BioVentures 2018 LLC, the manager of MPM Asset Management Investors BV2018 LLC		01/14/2026
**Signature of Reporting Person		Date
/s/ Ansbert Gadicke, manager of MPM Oncology Innovations Fund GP LLC		01/14/2026
**Signature of Reporting Person		Date
/s/ Ansbert Gadicke, manager of MPM Oncology Innovations Fund GP LLC, the general partner of MPM Oncology Innovations Fund, L.P.		01/14/2026
**Signature of Reporting Person		Date

Explanation of Responses:

*	If the form is filed by more than one reporting person, see Instruction 4(b)(v).
**	Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
(1)	The shares of common stock were issued upon conversion as follows: 556,810 by MPM BioVentures 2018, L.P. ("BV 2018"), 29,593 by MPM BioVentures 2018 (B), L.P. ("BV 2018(B)"), 10,988 by MPM Asset Management Investors BV2018 LLC ("AM BV2018"), 119,478 by MPM Oncology Innovations Fund, L.P. ("MPM Oncology") and 597,393 by Oncology Impact Private Investment Fund 2, L.P. ("MPM Oncology Impact"). MPM BioVentures 2018 GP LLC and MPM BioVentures 2018 LLC ("BV2018 LLC") are the direct and indirect general partners of BV 2018 and BV 2018(B). BV 2018 LLC is the manager of AM BV2018. Drs. Evnin and Gadicke are managing directors of BV 2018 LLC and managers of MPM Oncology Innovations Fund GP LLC, which is the general partner of MPM Oncology. Dr. Gadicke is the managing member of MPM Oncology Investments 2 LLC, which is the general partner of MPM Oncology Impact.
(2)	Each share of Series Seed Redeemable Convertible Preferred Stock, Series A Redeemable Convertible Preferred Stock and Series B Redeemable Convertible Preferred Stock automatically converted into shares of the Issuer's Common Stock on a 3.8044-for-1 basis into the number of shares of Common Stock shown in Column 7 without payment of further consideration upon the closing of the initial public offering of the Issuer's Common Stock. The Series Seed Redeemable Convertible Preferred Stock, Series A Redeemable Convertible Preferred Stock and Series B Redeemable Convertible Preferred Stock had no expiration date.
(3)	The Reporting Persons disclaim beneficial ownership of the securities except to the extent of his or its pecuniary interest therein.
(4)	The shares are held as follows: 341,709 by MPM Asset Management LLC ("MPM AM"), 556,810 by BV 2018, 29,593 by BV 2018(B), 10,988 by AM BV2018, 119,478 by MPM Oncology and 597,393 by MPM Oncology Impact. Dr. Gadicke is the manager of MPM AM.
(5)	The shares of common stock were issued upon conversion as follows: 2,505,648 by BV 2018, 133,170 by BV 2018(B), 49,452 by AM BV2018, 537,654 by MPM Oncology and 2,688,273 by MPM Oncology Impact.
(6)	The shares are held as follows: 341,709 by MPM AM, 3,062,458 by BV 2018, 162,763 by BV 2018(B), 60,440 by AM BV2018, 657,132 by MPM Oncology and 3,285,666 by MPM Oncology Impact.
(7)	The shares of common stock were issued upon conversion as follows: 668,173 by BV 2018, 35,512 by BV 2018(B), 13,187 by AM BV2018, 143,374 by MPM Oncology and 716,873 by MPM Oncology Impact.
(8)	The shares are held as follows: 341,709 by MPM AM, 3,730,631 by BV 2018, 198,275 by BV 2018(B), 73,627 by AM BV2018, 800,506 by MPM Oncology and 4,002,539 by MPM Oncology Impact.
(9)	The shares were purchased as follows: 219,897 by BV 2018, 8,689 by BV 2018(B), 4,284 by AM BV2018, 46,574 by MPM Oncology and 833,333 by MPM Oncology Impact.
(10)	The shares are held as follows: 341,709 by MPM AM, 3,950,528 by BV 2018, 206,964 by BV 2018(B), 77,911 by AM BV2018, 847,080 by MPM Oncology and 4,835,872 by MPM Oncology Impact.
Remarks: This filing is 1 of 2 identical filings due to limitations on number of Reporting Persons. See Form 4 filed by Ansbert Gadicke.

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