X0306 4 2021-12-02 0 0001808865 iTeos Therapeutics, Inc. ITOS 0001816196 Detheux Michel 139 MAIN STREET CAMBRIDGE MA 02142 0 1 0 0 Chief Executive Officer Common Stock 2021-12-20 4 M 0 9111 4.30 A 87311 D Common Stock 2021-12-20 4 S 0 9111 43.94 D 78200 D Common Stock 2021-12-21 4 M 0 19226 4.30 A 97426 D Common Stock 2021-12-21 4 S 0 13646 44.15 D 83780 D Common Stock 2021-12-21 4 S 0 5580 45.06 D 78200 D Common Stock 2021-12-22 4 M 0 1663 4.30 A 79863 D Common Stock 2021-12-22 4 S 0 1514 44.31 D 78349 D Common Stock 2021-12-22 4 S 0 149 44.92 D 78200 D Common Stock 2021-12-22 4 S 0 5007 44.62 D 73193 D Common Stock 2021-12-22 4 S 0 9493 45.37 D 63700 D Stock Option (Right to Buy) 4.30 2021-12-02 5 G 0 E 313442 0.00 D 2025-06-11 Common Stock 403442 90000 D Stock Option (Right to Buy) 4.30 2021-12-02 5 G 0 E 313442 0.00 A 2025-06-11 Common Stock 313442 313442 I By MG3A Stock Option (Right to Buy) 4.23 2021-12-02 5 G 0 E 185000 0.00 D 2030-05-01 Common Stock 340964 155964 D Stock Option (Right to Buy) 4.23 2021-12-02 5 G 0 E 185000 0.00 A 2030-05-01 Common Stock 185000 185000 I By MG3A Stock Option (Right to Buy) 6.15 2021-12-02 5 G 0 E 52700 0.00 D 2030-06-18 Common Stock 70244 17544 D Stock Option (Right to Buy) 6.15 2021-12-02 5 G 0 E 52700 0.00 A 2030-06-18 Common Stock 52700 52700 I By MG3A Stock Option (Right to Buy) 19.00 2021-12-02 5 G 0 E 776600 0.00 D 2030-07-23 Common Stock 1035424 258824 D Stock Option (Right to Buy) 19.00 2021-12-02 5 G 0 E 776600 0.00 A 2030-07-23 Common Stock 776600 776600 I By MG3A Stock Option (Right to Buy) 41.58 2021-12-02 5 G 0 E 106200 0.00 D 2031-03-01 Common Stock 144000 37800 D Stock Option (Right to Buy) 41.58 2021-12-02 5 G 0 E 106200 0.00 A 2031-03-01 Common Stock 106200 106200 I By MG3A Stock Option (Right to Buy) 4.30 2021-12-20 4 M 0 9111 0.00 D 2025-06-11 Common Stock 9111 80889 D Stock Option (Right to Buy) 4.30 2021-12-21 4 M 0 19226 0.00 D 2025-06-11 Common Stock 19226 61663 D Stock Option (Right to Buy) 4.30 2021-12-22 4 M 0 1663 0.00 D 2025-06-11 Common Stock 1663 60000 D The transaction was effected pursuant to a Rule 10b5-1 trading plan adopted by the reporting person on February 18, 2021. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $43.8 to $44.2, inclusive. The reporting person undertakes to provide to iTeos Therapeutics, Inc., any security holder of iTeos Therapeutics, Inc., 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 ranges set forth in this footnote. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $43.8 to $44.79, inclusive. The reporting person undertakes to provide to iTeos Therapeutics, Inc., any security holder of iTeos Therapeutics, Inc., 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 ranges set forth in this footnote. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $44.825 to $45.29, inclusive. The reporting person undertakes to provide to iTeos Therapeutics, Inc., any security holder of iTeos Therapeutics, Inc., 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 ranges set forth in this footnote. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $43.85 to $44.73, inclusive. The reporting person undertakes to provide to iTeos Therapeutics, Inc., any security holder of iTeos Therapeutics, Inc., 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 ranges set forth in this footnote. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $44.12 to $45.11, inclusive. The reporting person undertakes to provide to iTeos Therapeutics, Inc., any security holder of iTeos Therapeutics, Inc., 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 ranges set forth in this footnote. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $45.15 to $45.83, inclusive. The reporting person undertakes to provide to iTeos Therapeutics, Inc., any security holder of iTeos Therapeutics, Inc., 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 ranges set forth in this footnote. The reporting person transferred these stock options to MG3A, a Belgian partnership of which the reporting person is the manager and the reporting person's spouse is the successor manager. One-fourth of the shares subject to the stock option vested on January 1, 2019. Thereafter, 1/48 of the shares subject to the stock option vest on a monthly basis, subject to the reporting person's continuous service relationship with the Issuer through each applicable vesting date. One-fourth of the shares subject to the stock option vested on May 1, 2021. Thereafter, 1/48 of the shares subject to the stock option vest on a monthly basis, subject to the reporting person's continuous service relationship with the Issuer through each applicable vesting date. One-fourth of the shares subject to the stock option vested on June 1, 2021. Thereafter, 1/48 of the shares subject to the stock option vest on a monthly basis, subject to the reporting person's continuous service relationship with the Issuer through each applicable vesting date. One-fourth of the shares subject to the stock option vested on July 23, 2021. Thereafter, 1/48 of the shares subject to the stock option vest on a monthly basis, subject to the reporting person's continuous service relationship with the Issuer through each applicable vesting date. One-fourth of the shares subject to the stock option will vest on March 1, 2022, subject to the reporting person's continuous service relationship with the Issuer. Thereafter, 1/48 of the shares subject to the stock option vest on a monthly basis, subject to the reporting person's continuous service relationship with the Issuer through each applicable vesting date. /s/ Adi Osovsky, as Attorney-in-Fact 2021-12-22