SEPARATION AGREEMENT AND GENERAL RELEASE OF CLAIMS

Exhibit 10.15

SEPARATION AGREEMENT AND GENERAL RELEASE OF CLAIMS

This Separation and Release Agreement (“Agreement”) is made this 30^th day of September, 2014 by and between Henry B. Lowman, Ph.D. (“Executive”) and CytomX Therapeutics, Inc. (“Company”).

WHEREAS, Company and Executive will be separating their employment relationship, and Executive will transition from Chief Scientific Officer, to Consultant Chief Scientific Officer, to a member of Company’s Scientific Advisory Board;

WHEREAS, Company has offered Executive certain separation benefits in exchange for Executive’s commitments set forth in this agreement;

NOW THEREFORE, the parties agree as follows:

“SECTION 3. PAYMENT OF PRINCIPAL AND INTEREST. Subject to prepayment under Section 5, below, and acceleration under Section 6, below, the principal of and interest on this Note shall be due and payable in full on the earliest of (i) the Seventh Anniversary of the Issue Date, (ii) the sale or disposition of all or any portion of the Pledged Shares, or (iii) the thirtieth day in which the Maker has not provided service to the Holder either as an employee or a consultant.”

Your acceptance and non-revocation of this Release Agreement is a condition precedent to any of the Company’s obligations under this paragraph.

(a) In consideration of the Separation Benefits that you are receiving as provided in paragraph 3 above, and on behalf of yourself and your heirs, executors, administrators, successors, and assigns, you hereby waive, release, and hold harmless Company, its respective parents, subsidiaries, divisions, units, related companies, each and every past and present member, shareholder, investor, associate, affiliate, predecessor, successor and related entities, and all of their current or former agents, officers, directors, partners, representatives, attorneys, contractors, insurance companies, administrators, successors, assigns, current and former employees, plan administrators, insurers, and any other persons acting by, through, under, or in concert with any of the persons or entities listed in this subsection, and each of them (“Released Parties”), from any and all claims, rights, debts, liabilities, demands, causes of action, obligations, and damages, known or unknown, suspected or unsuspected, arising as of or prior to the date of your signature to this Release Agreement, under federal, state, local, or common law (the “Released Claims”), including but not limited to claims in any way related to your employment with the Released Parties, or the termination of your employment. The laws under which the Released Claims may arise include, but are not limited to, the Civil Rights Act of 1866, Title VII of the Civil Rights Act of 1964, the Civil Rights Act of 1991, the Employee Retirement Income Security Act of 1974, the Americans with Disabilities Act, as amended, the Worker Adjustment and Retraining Notification Act, the Age Discrimination in Employment Act, as amended, the Older Workers Benefit Protection Act, the California Labor Code, the California Business and Professions Code, all California Wage Orders, the California Fair Employment and Housing Act, the California Family Rights Act, and/or the laws prohibiting discrimination, harassment, and/or retaliation in any state in which you are employed, and any and all federal, state, and local employment laws, as well as any and all common law tort or contract theories under state federal or local laws. The Released Claims also include claims of discrimination or retaliation on the basis of workers’ compensation status, but do not include workers’ compensation claims. Nothing in this Release Agreement shall be construed to affect the Equal Employment Opportunity Commission’s (the “Commission”) or any state agency’s independent right and responsibility to enforce the law, nor does this Release Agreement affect your right to file a charge or participate in an investigation or proceeding conducted by either the Commission or any such state agency, although this Release Agreement does bar any claim that you might have to receive monetary damages in connection with any Commission or state agency proceeding concerning matters covered by this Release Agreement. Execution of this Release Agreement does not bar any claim that arises hereafter, including (without limitation) a claim for breach of this Release Agreement, any claim to indemnity under section 2802 of the California Labor Code, or any other claim that by law may not be released.

(b) You acknowledge that you have been advised by legal counsel that you are by this Release Agreement waiving claims pursuant to California Civil Code Section 1542 or the laws of other states similar hereto, and you expressly waive such rights as quoted below:

A GENERAL RELEASE DOES NOT EXTEND TO CLAIMS WHICH THE CREDITOR DOES NOT KNOW OR SUSPECT TO EXIST IN HIS/HER FAVOR AT THE TIME OF EXECUTING THE RELEASE, WHICH IF KNOWN BY HIM OR HER MUST HAVE MATERIALLY AFFECTED HIS OR HER SETTLEMENT WITH THE DEBTOR.

You hereby expressly waive any rights you may have under any other statute or common law principles of similar effect.

(c) You acknowledge and understand that the release of claims under the Age Discrimination in Employment Act (“ADEA”), 29 U.S.C. Section 621-634, is subject to special waiver protections under 29 U.S.C. Section 626(f). In accordance with that section, you specifically agree that you are knowingly and voluntarily releasing and waiving any rights or claims of discrimination under the ADEA. In particular you acknowledge that you understand that:

BY SIGNING BELOW, YOU ACKNOWLEDGE THAT YOU HAVE READ THIS RELEASE AGREEMENT, UNDERSTAND ITS TERMS AND EFFECT, AND AGREE TO IT VOLUNTARILY.

Appendix A

CytomX Therapeutics, Inc.

Shareholder Report

As of 09/30/2014

Holder Name Contains Lowman

SSN/Tax ID = Excluded

CytomX Therapeutics, Inc.

Personnel Summary

As of 09/30/2014

Holder Name Contains lowman

SSN/Tax ID = Excluded

Footnote(s):

The Exercise Price(s) Per Share in this report have been rounded to 4 decimal places for display purposes, although the actual price may be up to 15 decimal places as indicated on the individual security screen.