X0306 4 2021-05-17 0 0001808865 iTeos Therapeutics, Inc. ITOS 0001816213 McGrath Yvonne C/O ITEOS THERAPEUTICS, INC. 139 MAIN STREET CAMBRIDGE MA 02142 0 1 0 0 VP, Research and Development Common Stock 2021-05-17 4 M 0 7926 4.23 A 7926 D Common Stock 2021-05-17 4 S 0 5807 24.4148 D 2119 D Common Stock 2021-05-17 4 S 0 2029 25.4321 D 90 D Common Stock 2021-05-17 4 S 0 90 26.01 D 0 D Stock Option (Right to Buy) 4.23 2021-05-17 4 M 0 7926 0.00 D 2030-05-01 Common Stock 7926 118904 D The sales reported in this Form 4 were effected pursuant to a Rule 10b5-1 trading plan adopted by the reporting person on April 15, 2021. The proceeds of the sales are being used to satisfy the payment of Belgian tax obligations in connection with the grant of a stock option to the reporting person on March 1, 2021. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $24.17 to $24.90, 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 $25.00 to $25.95, 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. One-fourth of the shares subject to the stock option vest on the one-year anniversary of the vesting commencement date, subject to the reporting persons continuous service relationship with the Issuer through such date. Thereafter, 1/48 of the shares subject to the stock option vest on a monthly basis following the one-year anniversary of the vesting commencement date, subject to the reporting persons continuous service relationship with the Issuer through each applicable vesting date. /s/ Michel Detheux, as Attorney-in-Fact 2021-05-19