Sec Form 4 Filing - GADICKE ANSBERT @ iTeos Therapeutics, Inc. - 2021-04-07

FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person GADICKE ANSBERT 2. Issuer Name and Ticker or Trading Symbol iTeos Therapeutics, Inc. [ ITOS] 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 CAPITAL, 450 KENDALL STREET 3. Date of Earliest Transaction (MM/DD/YY) 04/07/2021 (Street) CAMBRIDGE, MA02142 4. If Amendment, Date Original Filed (MM/DD/YY) 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 (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 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 04/07/2021 S( 1 ) 5,295 ( 2 ) ( 3 ) D $ 32.07 ( 4 ) 6,056,925 I See Footnote ( 5 ) Common Stock 04/07/2021 S( 1 ) 3,083 ( 6 ) D $ 32.84 ( 7 ) 6,053,842 I See Footnote ( 8 ) Common Stock 04/07/2021 S( 1 ) 1,300 ( 9 ) D $ 33.84 ( 10 ) 6,052,542 I See Footnote ( 11 ) Common Stock 04/07/2021 J( 12 ) 15,670 ( 13 ) D $ 0 6,036,872 I See Footnote ( 14 ) Common Stock 04/08/2021 S( 1 ) 31,890 ( 15 ) D $ 30.51 ( 16 ) 6,004,982 I See Footnote ( 17 ) Common Stock 04/08/2021 S( 1 ) 414 ( 18 ) D $ 31.01 ( 19 ) 6,004,568 I See Footnote ( 20 )

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 (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 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 (MM/DD/YY) 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

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other GADICKE ANSBERT C/O MPM CAPITAL 450 KENDALL STREET CAMBRIDGE, MA02142 X UBS Oncology Impact Fund L.P. C/O MPM CAPITAL 450 KENDALL STREET CAMBRIDGE, MA02142 X MPM Oncology Impact Management LP C/O MPM CAPITAL 450 KENDALL STREET CAMBRIDGE, MA02142 X Oncology Impact Fund (Cayman) Management L.P. C/O MPM CAPITAL 450 KENDALL STREET CAMBRIDGE, MA02142 X MPM Oncology Impact Management GP LLC C/O MPM CAPITAL 450 KENDALL STREET CAMBRIDGE, MA02142 X Signatures /s/ Ansbert Gadicke 04/09/2021 Signature of Reporting Person Date /s/ Ansbert Gadicke, managing director of MPM Oncology Impact Management GP LLC, the general partner of MPM Oncology Impact Management LP, the general partner of Oncology Impact Fund (Cayman) Management L.P., the GP of UBS Oncology Impact Fund L.P. 04/09/2021 Signature of Reporting Person Date /s/ Ansbert Gadicke, managing director of MPM Oncology Impact Management GP LLC, the general partner of MPM Oncology Impact Management LP 04/09/2021 Signature of Reporting Person Date /s/ Ansbert Gadicke, managing director of MPM Oncology Impact Management GP LLC, the general partner of MPM Oncology Impact Management LP, the general partner of Oncology Impact Fund (Cayman) Management L.P. 04/09/2021 Signature of Reporting Person Date /s/ Ansbert Gadicke, managing director of MPM Oncology Impact Management GP LLC 04/09/2021 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Transaction effected pursuant to a plan established pursuant to Rule 10b5-1. ( 2 )The shares were sold as follows: 1,885 by MPM BioVentures 2014, L.P. ("BV 2014"), 65 by MPM Asset Management Investors BV2014 LLC ("AM BV2014"), 1,191 by MPM BioVentures 2018, L.P. ("BV 2018"), 23 by MPM Asset Management Investors BV2018 LLC ("AM BV2018") and 2,131 by UBS Oncology Impact Fund L.P. ("UBS Oncology"). MPM BioVentures 2014 GP LLC and MPM BioVentures 2014 LLC ("BV 2014 LLC") are the direct and indirect general partners of BV 2014 and BV 2014(B). BV 2014 LLC is the manager of AM BV2014. MPM BioVentures 2018 GP LLC and MPM BioVentures 2018 LLC ("BV 2018 LLC") are the direct and indirect general partners of BV 2018 and BV 2018(B). BV 2018 LLC is the manager of AM BV2018. Ansbert Gadicke is a managing director of BV 2014 LLC and BV 2018 LLC. ( 3 )MPM Oncology Impact Management GP LLC ("Oncology GP LLC") is the General Partner of MPM Oncology Impact Management LP, the General Partner of Oncology Impact Fund (Cayman) Management L.P., the General Partner of UBS Oncology Impact Fund, L.P. Ansbert Gadicke is the managing director of Oncology GP LLC. Each of the Reporting Persons disclaims beneficial ownership of the securities herein except to the extent of his or its respective pecuniary interest therein, if any. ( 4 )The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $31.50 to $32.42 inclusive. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote. ( 5 )The shares are held as follows: 2,082,002 by BV 2014, 138,985 by MPM BioVentures 2014(B), L.P. ("BV 2014(B)"), 71,662 by AM BV2014, 1,314,948 by BV 2018, 69,951 by MPM BioVentures 2018(B), L.P. ("BV 2018(B)"), 25,951 by AM BV2018 and 2,353,426 by UBS Oncology. Each of the Reporting Persons disclaims beneficial ownership of the securities herein except to the extent of his or its respective pecuniary interest therein, if any. ( 6 )The shares were sold as follows: 1,097 by BV 2014, 38 by AM BV2014, 693 by BV 2018, 14 by AM BV2018 and 1,241 by UBS Oncology. ( 7 )The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $32.50 to $33.265 inclusive. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote. ( 8 )The shares are held as follows: 2,080,905 by BV 2014, 138,985 by BV 2014(B), 71,624 by AM BV2014, 1,314,255 by BV 2018, 69,951 by BV 2018(B), 25,937 by AM BV2018 and 2,352,185 by UBS Oncology. Each of the Reporting Persons disclaims beneficial ownership of the securities herein except to the extent of his or its respective pecuniary interest therein, if any. ( 9 )The shares were sold as follows: 463 by BV 2014, 16 by AM BV2014, 292 by BV 2018, 6 by AM BV2018 and 523 by UBS Oncology. ( 10 )The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $33.50 to $34.25 inclusive. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote. ( 11 )The shares are held as follows: 2,080,442 by BV 2014, 138,985 by BV 2014(B), 71,608 by AM BV2014, 1,313,963 by BV 2018, 69,951 by BV 2018(B), 25,931 by AM BV2018 and 2,351,662 by UBS Oncology. Each of the Reporting Persons disclaims beneficial ownership of the securities herein except to the extent of his or its respective pecuniary interest therein, if any. ( 12 )Represents a pro rata in-kind distribution from BV 2014(B) and BV 2018(B) to its respectve limited partners for no consideration. ( 13 )The shares were distributed as follows: 10,424 shares by BV 2014(B) and 5,246 shares by BV 2018(B). ( 14 )The shares are held as follows: 2,080,442 by BV 2014, 128,561 by BV 2014(B), 71,608 by AM BV2014, 1,313,963 by BV 2018, 64,705 by BV 2018(B), 25,931 by AM BV2018 and 2,351,662 by UBS Oncology. Each of the Reporting Persons disclaims beneficial ownership of the securities herein except to the extent of his or its respective pecuniary interest therein, if any. ( 15 )The shares were sold as follows: 11,354 by BV 2014, 391 by AM BV2014, 7,171 by BV 2018, 141 by AM BV2018 and 12,833 by UBS Oncology. ( 16 )The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $29.95 to $30.92 inclusive. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote. ( 17 )The shares are held as follows: 2,069,088 by BV 2014, 128,561 by BV 2014(B), 71,217 by AM BV2014, 1,306,792 by BV 2018, 64,705 by BV 2018(B), 25,790 by AM BV2018 and 2,338,829 by UBS Oncology. Each of the Reporting Persons disclaims beneficial ownership of the securities herein except to the extent of his or its respective pecuniary interest therein, if any. ( 18 )The shares were sold as follows: 147 by BV 2014, 5 by AM BV2014, 93 by BV 2018, 2 by AM BV2018 and 167 by UBS Oncology. ( 19 )The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $30.945 to $31.19 inclusive. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote. ( 20 )The shares are held as follows: 2,068,941 by BV 2014, 128,561 by BV 2014(B), 71,212 by AM BV2014, 1,306,699 by BV 2018, 64,705 by BV 2018(B), 25,788 by AM BV2018 and 2,338,662 by UBS Oncology. Each of the Reporting Persons disclaims beneficial ownership of the securities herein except to the extent of his or its respective pecuniary interest therein, if any.

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