As filed with the Securities and Exchange Commission on March 24, 2021

Registration No. 333-

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM S-8

REGISTRATION STATEMENT

Under

The Securities Act of 1933

ITEOS THERAPEUTICS, INC.

(Exact name of registrant as specified in its charter)

139 Main Street

Cambridge, MA 02142

(339) 217-0162

(Address, including zip code and telephone number, including area code, of Registrant’s principal executive offices)

iTeos Therapeutics, Inc. 2020 Stock Option and Incentive Plan

iTeos Therapeutics, Inc. 2020 Employee Stock Purchase Plan

(Full title of the plans)

Michel Detheux, Ph.D.

Chief Executive Officer

iTeos Therapeutics, Inc.

139 Main Street

Cambridge, MA 02142

(339) 217-0162

(Name, address, including zip code, and telephone number, including area code, of agent for service)

Copies to:

Mitchell S. Bloom, Esq.

Danielle Lauzon, Esq.

Stephanie A. Richards, Esq.

Goodwin Procter LLP

100 Northern Avenue

Boston, Massachusetts 02210

(617) 570-1000

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company, or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company,” and “emerging growth company” in Rule 12b-2 of the Exchange Act.

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 7(a)(2)(B) of the Securities Act. ☐

CALCULATION OF REGISTRATION FEE

Proposed sales to take place as soon after the effective date of the Registration Statement as awards are granted, exercised or distributed under the above-named plans.

EXPLANATORY NOTE

This Registration Statement on Form S-8 is filed for the purposes of registering (i) an additional 1,752,237 shares of common stock, par value $0. 001 per share (“Common Stock”), of iTeos Therapeutics, Inc. (the “Registrant”) that may be issued pursuant to the iTeos Therapeutics, Inc. 2020 Stock Option and Incentive Plan (the “2020 Plan”) and (ii) an additional 350,447 shares of Common Stock of the Registrant that may be issued pursuant to the iTeos Therapeutics, Inc. 2020 Employee Stock Purchase Plan (the “2020 ESPP”). The number of shares of Common Stock reserved and available for issuance under the 2020 Plan is subject to an automatic annual increase on each January 1 by an amount equal to up to five percent of the number of shares of Common Stock issued and outstanding on the immediately preceding December 31 or such lesser number of shares of Common Stock as determined by the Administrator (as defined in the 2020 Plan). Accordingly, on January 1, 2021, the number of shares of Common Stock reserved and available for issuance under the 2020 Plan increased by 1,752,237. This Registration Statement registers these additional 1,752,237 shares of Common Stock. The additional shares are of the same class as other securities relating to the 2020 Plan for which the Registrant’s registration statement filed on Form S-8 (Registration No. 333-240144) on July 28, 2020, is effective. The number of shares of Common Stock reserved and available for issuance under the 2020 ESPP is subject to an automatic annual increase on each January 1 by an amount equal to the least of one percent of the number of shares of Common Stock issued and outstanding on the immediately preceding December 31, 634,969 shares of Common Stock or such lesser number of shares of Common Stock as determined by the Administrator (as defined in the 2020 ESPP). Accordingly, on January 1, 2021, the number of shares of Common Stock reserved and available for issuance under the 2020 ESPP increased by 350,447 This Registration Statement registers these additional 350,447 shares of Common Stock. The additional shares are of the same class as other securities relating to the 2020 ESPP for which the Registrant’s registration statement filed on Form S-8 (Registration No. 333-240144) on July 28, 2020, is effective. The information contained in the Registrant’s registration statement on Form S-8 (Registration No. 333-240144) is hereby incorporated by reference pursuant to General Instruction E.

Part II

EXHIBIT INDEX

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, the registrant certifies that it has reasonable grounds to believe that it meets all of the requirements for filing on Form S-8 and has duly caused this registration statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Cambridge, State of Massachusetts, on this 24th day of March, 2021.

POWER OF ATTORNEY AND SIGNATURES

KNOW ALL PERSONS BY THESE PRESENTS, that each person whose signature appears below constitutes and appoints Michel Detheux and Matthew Call, and each of them, either of whom may act without the joinder of the other, as his true and lawful attorneys-in-fact and agents with full power of substitution and re-substitution, for him or her and in his or her name, place and stead, in any and all capacities, to sign any and all amendments (including post-effective amendments) to this registration statement on Form S-8, and to file the same, with all exhibits thereto and all documents in connection therewith, with the Securities and Exchange Commission, granting unto said attorneys-in-fact and agents, and each of them, full power and authority to do and perform each and every act and thing requisite and necessary to be done in and about the premises, as fully to all intents and purposes as he might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents or any of them, or his or their substitute or substitutes, may lawfully do or cause to be done or by virtue hereof.

Pursuant to the requirements of the Securities Act of 1933, this Registration Statement has been signed by the following persons in the capacities and on the date indicated.

Exhibit 5.1

March 24, 2021

iTeos Therapeutics, Inc.

139 Main Street

Cambridge, Massachusetts 02142

We have acted as counsel to you in connection with your filing of a Registration Statement on Form S-8 (the “Registration Statement”) pursuant to the Securities Act of 1933, as amended (the “Securities Act”), on or about the date hereof relating to an aggregate of 2,102,684 shares (the “Shares”) of Common Stock, $0.001 par value per share (“Common Stock”), of iTeos Therapeutics, Inc., a Delaware corporation (the “Company”), that may be issued pursuant to the Company’s 2020 Stock Option and Incentive Plan and 2020 Employee Stock Purchase Plan (collectively, the “Plans”).

We have reviewed such documents and made such examination of law as we have deemed appropriate to give the opinions set forth below. We have relied, without independent verification, on certificates of public officials and, as to matters of fact material to the opinion set forth below, on certificates of officers of the Company.

The opinion set forth below is limited to the Delaware General Corporation Law.

For purposes of the opinion set forth below, we have assumed that no event occurs that causes the number of authorized shares of Common Stock available for issuance by the Company to be less than the number of then unissued Shares.

Based on the foregoing, we are of the opinion that the Shares have been duly authorized and, upon issuance and delivery against payment therefor in accordance with the terms of the Plans, will be validly issued, fully paid and nonassessable.

We hereby consent to the inclusion of this opinion as Exhibit 5.1 to the Registration Statement. In giving our consent, we do not admit that we are in the category of persons whose consent is required under Section 7 of the Securities Act or the rules and regulations thereunder.

Exhibit 23.1

CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

We consent to the incorporation by reference in this Registration Statement on Form S-8 of our report dated March 24, 2021 relating to the financial statements of iTeos Therapeutics, Inc. appearing in the Annual Report on Form 10-K of iTeos Therapeutics, Inc. for the year ended December 31, 2020.

/s/ Deloitte Bedrijfsrevisoren/Réviseurs d’Entreprises CVBA/SCRL

Zaventem, Belgium

March 24, 2021