Common Stock

ITEOS THERAPEUTICS, INC.

321 ARSENAL STREET, WATERTOWN, MA, 02472

The entities and persons filing this statement are MPM BioVentures 2014, L.P. ("BV 2014"), MPM BioVentures 2014 (B), L.P. ("BV 2014(B)"), MPM Asset Management Investors BV2014 LLC ("AM BV2014 LLC"), MPM BioVentures 2018, L.P. ("BV 2018"), MPM BioVentures 2018 (B), L.P. ("BV 2018(B)"), MPM Asset Management Investors BV2018 LLC ("AM BV2018 LLC"), UBS Oncology Impact Fund L.P. ("UBS Oncology"), MPM BioVentures 2014 GP LLC ("BV 2014 GP"), MPM BioVentures 2014 LLC ("BV 2014 LLC"), MPM BioVentures 2018 GP LLC ("BV 2018 GP"), MPM BioVentures 2018 LLC ("BV 2018 LLC"), Oncology Impact Fund (Cayman) Management LP ("Oncology Cayman") and MPM BioImpact LLC ("BioImpact") (collectively, the "MPM Entities") and Ansbert Gadicke, Luke Evnin and Todd Foley (collectively, the "Listed Persons" and, together with the MPM Entities, the "Filing Persons"). The Filing Persons expressly disclaim status as a "group"; for purposes of this Schedule 13D.

The address of the principal place of business for each of the MPM Entities and Ansbert Gadicke, Luke Evnin and Todd Foley is 399 Boylston Street, Suite 1100, Boston, MA 02116.

The principal business of each of the Filing Persons is the venture capital investment business.

During the last five years, none of the Filing Persons has been 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.

Each of the Listed Persons is a United States citizen and each of the MPM Entities is a Delaware limited partnership or limited liability company, other than UBS Oncology and Oncology Cayman which are Cayman Islands limited partnerships. In accordance with the provisions of General Instruction C to Schedule 13D, information concerning the managers and each other person controlling the general partners of the MPM Entities required by Item 2 of Schedule 13D is listed on Schedule 1 to this Amendment No. 4 and is incorporated by reference herein.

See rows (11) and (13) of the Filing Persons Owner Profile of this Amendment No. 4 for the aggregate number of shares of Common Stock and percentages of the shares of Common Stock beneficially owned by the Filing Person. The Common Stock are held as follows: * 621,312 shares are held directly by BV 2014; * 39,135 shares are held directly by BV 2014(B); * 21,385 shares are held directly by AM BV2014 LLC; * 392,407 shares are held directly by BV 2018; * 19,697 shares are held directly by BV 2018(B); * 7,749 shares are held directly by AM BV2018 LLC; and * 702,311 shares are held directly by UBS Oncology. BV 2014 GP and BV 2014 LLC are the direct and indirect general partners of BV 2014 and BV 2014(B) and, accordingly, may be deemed to beneficially own the shares held by BV 2014 and BV 2014(B). BV 2014 LLC is the managing member of AM BV2014 LLC and, accordingly, may be deemed to beneficially own the shares held by AM BV2014 LLC. BV 2018 GP and BV 2018 LLC are the direct and indirect general partners of BV 2018 and BV 2018(B) and, accordingly, may be deemed to beneficially own the shares held by BV 2018 and BV 2018(B). BV 2018 LLC is the managing member of AM BV2018 LLC and, accordingly, may be deemed to beneficially own the shares held by AM BV2018 LLC. BioImpact and Oncology Cayman are the direct and indirect general partners of UBS Oncology and, accordingly, may be deemed to beneficially own the shares held by UBS Oncology. Drs. Gadicke and Evnin and Mr. Foley are the managing directors of BV 2014 LLC and BV 2018 LLC and, accordingly, may be deemed to beneficially own the shares held by BV 2014, BV 2014(B), AM BV2014 LLC, BV 2018, BV 2018(B), AM BV2018 LLC. Dr. Gadicke is the managing partner of BioImpact and, accordingly may be deemed to beneficially own the shares held by UBS Oncology. Calculation of the percentage of the shares of Common Stock beneficially owned is based upon 38,273,795 shares of Common Stock outstanding as of April 22, 2025, as reported in the Issuer's Form 10-Q filed with the SEC on April 28, 2025.

See rows (7) through (10) of the Filing Persons Owner Profile of this Amendment No. 4 for the number of shares as to which there is sole power to vote or to direct the vote, sole power to dispose or to direct the disposition, or shared power to dispose or to direct the disposition.

The Reporting Persons sold the following Common Stock in the open market in the sixty days preceding the date of this filing: Date Price Average BV 2014 BV2014(B) AM BV2014 BV 2018 BV 2018(B) AM BV2018 UBS Range Price LLC LLC Oncology 5/13/25 $7.73-$8.34 $8.06 355,406 22,386 12,233 224,467 11,267 4,432 401,740 5/14/25 $7.32-$7.965 $7.38 567,862 35,768 19,546 358,649 18,002 7,082 641,892

Inapplicable.

All Filing Persons ceased to be the beneficial owners of more than five percent of the Common Stock on May 14, 2025.