As filed with the Securities and Exchange Commission on February 27, 2019

Registration No. 333-                

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM S-8

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

CytomX Therapeutics, Inc.

(Exact name of Registrant as specified in its charter)

151 Oyster Point Blvd.

Suite 400

South San Francisco, CA 94080

(650) 515-3185

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

CytomX Therapeutics, Inc. 2015 Equity Incentive Plan

CytomX Therapeutics, Inc. Employee Stock Purchase Plan

(Full Title of the Plan)

Sean A. McCarthy, D.Phil.

President and Chief Executive Officer

CytomX Therapeutics, Inc.

151 Oyster Point Blvd., Suite 400

South San Francisco, CA 94080

(650) 515-3185

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

Copies to:

Mark V. Roeder, Esq.

Latham & Watkins LLP

140 Scott Drive

Menlo Park, California 94025

(650) 328-4600

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, 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 comply 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 sale to take place as soon after the effective date of the

registration statement as awards under the plans are exercised and/or vest.

EXPLANATORY NOTE

This Registration Statement on Form S-8 is being filed for the purpose of registering an additional 2,254,160 shares of the Registrant’s common stock issuable under the following employee benefit plans for which Registration Statements of the Registrant on Form S-8 (File Nos. 333-207694, 333-209992, 333-215795 and 333-223491) are effective: (i) the CytomX Therapeutics, Inc. 2015 Equity Incentive Plan, as a result of the operation of an automatic annual increase provision therein, which added 1,803,328 shares of common stock, and (ii) the CytomX Therapeutics, Inc. Employee Stock Purchase Plan, as a result of the operation of an automatic annual increase provision therein, which added 450,832 shares of common stock.

INCORPORATION BY REFERENCE OF CONTENTS OF REGISTRATION STATEMENT ON

FORM S-8

Pursuant to Instruction E of Form S-8, the contents of the Registration Statements on Form S-8 filed with the Securities and Exchange Commission on October 30, 2015 (File No. 333-207694), March 7, 2016 (File No. 333-209992), January 27, 2017 (File No. 333-215795) and March 7, 2018 (File No. 333-223491) are incorporated by reference herein; except for Item 8 which is being updated by this Registration Statement.

Item 8. Exhibits

#Indicates management contract or compensatory plan.

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, as amended, 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 South San Francisco, California, on this 27^th day of February, 2019.

POWER OF ATTORNEY

KNOW ALL PERSONS BY THESE PRESENTS, that each person whose signature appears below does hereby constitute and appoint Sean A. McCarthy and Debanjan Ray, and each of them, with full power of substitution and full power to act without the other, his or her true and lawful attorney-in-fact and agent to act for him or her 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, and to file this registration statement, with all exhibits thereto, and other 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 order to effectuate the same as fully, to all intents and purposes, as they or he or she might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents, or any of them, may lawfully do or cause to be done by virtue hereof.

Pursuant to the requirements of the Securities Act of 1933, as amended, this registration statement has been signed by the following persons in the capacities and on the date indicated.

Exhibit 5.1

		140 Scott Drive Menlo Park, California 94025 Tel: +1.650.328.4600 Fax: +1.650.463.2600 www.lw.com
		FIRM / AFFILIATE OFFICES
		Beijing		Moscow
		Boston		Munich
		Brussels		New York
		Century City		Orange County
February 27, 2019		Chicago		Paris
		Dubai		Riyadh
		Düsseldorf		Rome
		Frankfurt		San Diego
		Hamburg		San Francisco
		Hong Kong		Seoul
		Houston		Shanghai
		London		Silicon Valley
		Los Angeles		Singapore
		Madrid		Tokyo
		Milan		Washington, D.C.

CytomX Therapeutics, Inc.

151 Oyster Point Blvd., Suite 400

South San Francisco, CA 94080

Ladies and Gentlemen:

We have acted as special counsel to CytomX Therapeutics, Inc., a Delaware corporation (the “Company”), in connection with the registration by the Company of an aggregate of 2,254,160 shares of common stock of the Company, par value $0.00001 per share (the “Common Stock”), consisting of 1,803,328 shares of Common Stock (the “2015 Plan Shares”) issuable under the CytomX Therapeutics, Inc. 2015 Equity Incentive Plan (the “2015 Plan”) and 450,832 shares of Common Stock (the “ESPP Shares” and, together with the 2015 Plan Shares, the “Shares”) issuable under the CytomX Therapeutics, Inc. Employee Stock Purchase Plan (the “ESPP” and together with the 2015 Plan, the “Plans”).

The Shares are included in a registration statement on Form S–8 under the Securities Act of 1933, as amended (the “Act”), filed with the Securities and Exchange Commission (the “Commission”) on February 27, 2019 (the “Registration Statement”). This opinion is being furnished in connection with the requirements of Item 601(b)(5) of Regulation S-K under the Act, and no opinion is expressed herein as to any matter pertaining to the contents of the Registration Statement or the related prospectuses, other than as expressly stated herein with respect to the issue of the Shares.

As such counsel, we have examined such matters of fact and questions of law as we have considered appropriate for purposes of this letter. With your consent, we have relied upon certificates and other assurances of officers of the Company and others as to factual matters without having independently verified such factual matters. We are opining herein as to the General Corporation Law of the State of Delaware (the “DGCL”), and we express no opinion with respect to any other laws.

February 27, 2019

Page 2

Subject to the foregoing and the other matters set forth herein, it is our opinion that, as of the date hereof, when the Shares shall have been duly registered on the books of the transfer agent and registrar therefor in the name or on behalf of the purchasers and have been issued by the Company against payment therefor in the circumstances contemplated by the Plans, assuming in each case that the individual issuances, grants or awards under the Plans are duly authorized by all necessary corporate action and duly issued, granted or awarded and exercised in accordance with the requirements of law and the Plans (and the agreements and awards duly adopted thereunder and in accordance therewith), the issuance and sale of the Shares will have been duly authorized by all necessary corporate action of the Company, and the Shares will be validly issued, fully paid and nonassessable. In rendering the foregoing opinion, we have assumed that the Company will comply with all applicable notice requirements regarding uncertificated shares provided in the DGCL.

This opinion is for your benefit in connection with the Registration Statement and may be relied upon by you and by persons entitled to rely upon it pursuant to the applicable provisions of the Act. We consent to your filing this opinion as an exhibit to the Registration Statement. In giving such consent, we do not thereby admit that we are in the category of persons whose consent is required under Section 7 of the Act or the rules and regulations of the Commission thereunder.

Exhibit 23.1

CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

We consent to the incorporation by reference in the Registration Statement (Form S-8) pertaining to the CytomX Therapeutics, Inc. 2015 Equity Incentive Plan and the CytomX Therapeutics, Inc. Employee Stock Purchase Plan of our reports dated February 27, 2019, with respect to the financial statements of CytomX Therapeutics, Inc. and the effectiveness of internal control over financial reporting of CytomX Therapeutics, Inc. included in its Annual Report (Form 10-K) for the year ended December 31, 2018, filed with the Securities and Exchange Commission.

/s/ Ernst & Young LLP

Redwood City, California

February 27, 2019

Exhibit 23.2

CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

We hereby consent to the incorporation by reference in this Registration Statement on Form S-8 of CytomX Therapeutics, Inc. of our report dated March 2, 2017 relating to the financial statements, which appears in CytomX Therapeutics, Inc.’s Annual Report on Form 10-K for the year ended December 31, 2018.

/s/ PricewaterhouseCoopers LLP

San Jose, CA

February 27, 2019