Exhibit 10.3

Certain identified information has been excluded from the exhibit because it is both (i) not material and (ii) may be competitively harmful if publicly disclosed.

AmendmentNo.3 to the

CollaborationandLicenseAgreement

This Amendment No. 3(“Amendment”) totheCollaborationandLicense Agreement effectiveNovember 16,2022asamendedbyAmendmentNo.1effectiveJune28,2024andAmendmentNo.2effectiveOctober 7, 2025 (collectively the “Agreement”) by and between CytomX Therapeutics, Inc., having an address at 151 Oyster Point Blvd., Suite 400, South San Francisco, California 94080, U.S.A. (“CytomX”), and Regeneron Pharmaceuticals, Inc., a New York company with a business address located at 777 Old Saw Mill River Road, Tarrytown, NY 10591, U.S.A. (“Regeneron”) shall be effective as of May 16, 2026 (“Amendment No. 3 Effective Date”). All capitalized terms not otherwise defined herein shall have the meanings ascribed to such terms in the Agreement.

WHEREAS, Regeneron and CytomX wish to extend the period within which Regeneron may nominate certain Collaboration Programs;

NOW THEREFORE, inconsideration of theforegoing andtheagreementsbelow, andfor other goodand valuable consideration, the receipt and sufficiency of which are hereby acknowledged, the Parties hereby agree as follows:

1.

Section1.82oftheAgreementshallbeamendedasfollows:

“Section1.82“Program SelectionPeriod”means a period of [***] commencing upon the Effective Date of the Agreement, and ending on [***].”

2.

Except as specifically amended herein, all other terms of the Agreement shall remain in full force and effect. The Parties may execute this Amendment in counterparts, each of which is deemed an original, but all of which together constitute one and the same agreement.The Amendment may be executed or delivered electronically or by facsimile transmission, and the Parties hereby agree that any electronic, digital, or facsimilesignatures hereto are legal, valid and enforceable as originals.

IN WITNESS WHEREOF, the Parties heretohave executedthis Amendment No.3 as of theAmendment No. 3 Effective Date.