Sec Form 4 Filing - MPM BIOVENTURES 2018, L.P. @ iTeos Therapeutics, Inc. - 2021-11-17

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 MPM BIOVENTURES 2018, L.P. 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) 11/17/2021 (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 11/17/2021 J( 1 ) 15,671( 2 ) D $ 0 3,119,320 I See Footnote( 3 ) Common Stock 11/22/2021 S( 4 ) 9,307( 5 ) D $ 37.16( 6 ) 3,110,013 I See Footnote( 7 ) Common Stock 11/22/2021 S( 4 ) 11,807( 8 ) D $ 37.81( 9 ) 3,098,206 I See Footnote( 10 ) Common Stock 11/23/2021 S( 4 ) 19,645( 11 ) D $ 36.21( 12 ) 3,078,561 I See Footnote( 13 ) Common Stock 11/23/2021 S( 4 ) 359( 14 ) D $ 36.5( 15 ) 3,078,202 I See Footnote( 16 ) Common Stock 11/24/2021 S( 4 ) 4,868( 17 ) D $ 35.2( 18 ) 3,073,334 I See Footnote( 19 ) Common Stock 11/24/2021 S( 4 ) 18,343( 20 ) D $ 36.05( 21 ) 3,054,991 I See Footnote( 22 ) Common Stock 11/24/2021 S( 4 ) 13,126( 23 ) D $ 37.02( 24 ) 3,041,865 I See Footnote( 25 )

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 MPM BIOVENTURES 2018, L.P. C/O MPM CAPITAL 450 KENDALL STREET CAMBRIDGE, MA02142 X MPM BioVentures 2018 LLC C/O MPM CAPITAL 450 KENDALL STREET CAMBRIDGE, MA02142 X MPM BioVentures 2018 GP LLC C/O MPM CAPITAL 450 KENDALL STREET CAMBRIDGE, MA02142 X Signatures /s/ Ansbert Gadicke, managing director of MPM BioVentures 2018 LLC, the managing member of MPM BioVentures 2018 GP LLC, the general partner of MPM BioVentures 2018, L.P. 11/24/2021 Signature of Reporting Person Date /s/ Ansbert Gadicke, managing director of MPM BioVentures 2018 LLC 11/24/2021 Signature of Reporting Person Date /s/ Ansbert Gadicke, managing director of MPM BioVentures 2018 LLC, the managing member of MPM BioVentures 2018 GP LLC 11/24/2021 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Represents a pro rata in-kind distribution from MPM BioVentures 2014(B), L.P. ("BV 2014(B)") and MPM BioVentures 2018(B), L.P. ("BV 2018(B)") to its respectve limited partners for no consideration. ( 2 )The shares were distributed as follows: 10,424 by BV 2014(B) and 5,247 by BV 2018(B). ( 3 )The shares are held as follows: 1,771,303 by MPM BioVentures 2014, L.P. ("BV 2014"), 97,289 by BV2014(B), 60,967 by MPM Asset Management Investors BV2014 LLC ("AM BV2014"), 1,118,717 by MPM BioVentures 2018, L.P. ("BV 2018"), 48,966 by BV 2018(B) and 22,078 by MPM Asset Management Investors BV2018 LLC ("AM BV2018"). 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. Messrs. Evnin and Foley are managing directors of BV 2014 LLC and BV 2018 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 )Transaction effected pursuant to a plan established pursuant to Rule 10b5-1. ( 5 )The shares were sold as follows: 5,545 by BV 2014, 191 by AM BV2014, 3,502 by BV 2018 and 69 by AM BV2018. ( 6 )The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $36.58 to $37.555 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. ( 7 )The shares are held as follows: 1,765,758 by BV 2014, 97,289 by, 60,776 by AM BV2014, 1,115,215 by BV 2018, 48,966 by BV 2018(B) and 22,009 by AM BV2018. 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. ( 8 )The shares were sold as follows: 7,034 by BV 2014, 242 by AM BV2014, 4,443 by BV 2018 and 88 by AM BV2018. ( 9 )The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $37.58 to $38.16 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. ( 10 )The shares are held as follows: 1,758,724 by BV 2014, 97,289 by BV 2014(B), 60,534 by AM BV2014, 1,110,772 by BV 2018, 48,966 by BV 2018(B) and 21,921 by AM BV2018. 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. ( 11 )The shares were sold as follows: 11,704 by BV 2014, 403 by AM BV2014, 7,392 by BV 2018 and 146 by AM BV2018. ( 12 )The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $35.46 to $36.45 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. ( 13 )The shares are held as follows: 1,747,020 by BV 2014, 97,289 by BV 2014(B), 60,131 by AM BV2014, 1,103,380 by BV 2018, 48,966 by BV 2018(B) and 21,775 by AM BV2018. 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. ( 14 )The shares were sold as follows: 214 by BV 2014, 7 by AM BV2014, 135 by BV 2018 and 3 by AM BV2018. ( 15 )The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $36.48 to $36.52 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. ( 16 )The shares are held as follows: 1,746,806 by BV 2014, 97,289 by BV 2014(B), 60,124 by AM BV2014, 1,103,245 by BV 2018, 48,966 by BV 2018(B) and 21,772 by AM BV2018. 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. ( 17 )The shares were sold as follows: 2,900 by BV 2014, 100 by AM BV2014, 1,832 by BV 2018 and 36 by AM BV2018. ( 18 )The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $34.82 to $35.78 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. ( 19 )The shares are held as follows: 1,743,906 by BV 2014, 97,289 by BV 2014(B), 60,024 by AM BV2014, 1,101,413 by BV 2018, 48,966 by BV 2018(B) and 21,736 by AM BV2018. 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. ( 20 )The shares were sold as follows: 10,929 by BV 2014, 376 by AM BV2014, 6,902 by BV 2018 and 136 by AM BV2018. ( 21 )The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $35.83 to $36.81 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. ( 22 )The shares are held as follows: 1,732,977 by BV 2014, 97,289 by BV 2014(B), 59,648 by AM BV2014, 1,094,511 by BV 2018, 48,966 by BV 2018(B) and 21,600 by AM BV2018. 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. ( 23 )The shares were sold as follows: 7,820 by BV 2014, 269 by AM BV2014, 4,939 by BV 2018 and 98 by AM BV2018. ( 24 )The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $36.85 to $37.27 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. ( 25 )The shares are held as follows: 1,725,157 by BV 2014, 97,289 by BV 2014(B), 59,379 by AM BV2014, 1,089,572 by BV 2018, 48,966 by BV 2018(B) and 21,502 by AM BV2018. 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.

Remarks: See Form 4 for MPM BioVentures 2014, L.P for additional members of this joint filing.

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.

* 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).

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