UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 14A

Proxy Statement Pursuant to Section 14(a) of the

Securities Exchange Act of 1934

(Amendment No. )


Filed by the Registrant ☒			Filed by a Party other than the Registrant ☐

Check the appropriate box:

☐	Preliminary Proxy Statement

☐	Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2))

☒	Definitive Proxy Statement

☐	Definitive Additional Materials

☐	Soliciting Material Pursuant to § 240.14a-12

CytomX Therapeutics, Inc.

(Name of Registrant as Specified In Its Charter)

(Name of Person(s) Filing Proxy Statement, if other than the Registrant)

Payment of Filing Fee (Check all boxes that apply):

☒	No fee required.

☐	Fee paid previously with preliminary materials.

☐	Fee computed on table in exhibit required by Item 25(b) per Exchange Act Rules 14a-6(i)(1) and 0-11.

TABLE OF CONTENTS

151 Oyster Point Boulevard, Suite 400

South San Francisco, California 94080

NOTICE OF ANNUAL MEETING OF STOCKHOLDERS

TO BE HELD ON JUNE 17, 2026

AT 1:30 P.M. PACIFIC TIME

Dear Stockholder:

You are cordially invited to attend the 2026 Annual Meeting of Stockholders of CytomX Therapeutics, Inc., a Delaware corporation (the “Company” or “CytomX”). The 2026 Annual Meeting of Stockholders will be held on June 17, 2026, at 1:30 p.m., Pacific Time. The 2026 Annual Meeting of Stockholders will be convened and held entirely online to support and facilitate stockholder participation. You will be able to attend and participate online in the 2026 Annual Meeting of Stockholders by visiting www.virtualshareholdermeeting.com/CTMX2026, where you will be able to listen to the meeting live, submit questions, and vote.

The 2026 Annual Meeting of Stockholders is being convened to conduct the following business:

1.	To elect two directors with terms to expire at the 2029 Annual Meeting of Stockholders;

2.	To ratify the selection of Ernst & Young LLP as our independent registered public accounting firm for the fiscal year ending December 31, 2026;

3	To approve an amendment to CytomX’s Amended and Restated Certificate of Incorporation to increase the number of authorized shares of common stock from 300,000,000 shares to 600,000,000 shares;

4.	To approve an amendment to CytomX’s Amended and Restated 2015 Equity Incentive Plan;

5.	To approve an amendment to CytomX’s Amended and Restated Employee Stock Purchase Plan;

6.	To approve, on a non-binding advisory basis, the compensation of the Company’s named executive officers as disclosed in the Proxy Statement accompanying this Notice of Annual Meeting of Stockholders;

7.	To hold a non-binding advisory vote on the frequency of future advisory votes by stockholders on the compensation of the Company’s named executive officers; and

8.	To conduct any other business properly brought before the 2026 Annual Meeting of Stockholders.

These items of business are more fully described in the Proxy Statement accompanying this Notice of Annual Meeting of Stockholders. The record date for the 2026 Annual Meeting of Stockholders is April 20, 2026. Only stockholders of record at the close of business on that date are entitled to notice of, and to vote at, the 2026 Annual Meeting of Stockholders or any adjournment thereof.

The Board of Directors recommends that you vote as follows on the matters to be presented to stockholders at the 2026 Annual Meeting of Stockholders:

1.	FOR the election of the director nominees named in Proposal No. 1 of the Proxy Statement;

2.	FOR the ratification of the selection of Ernst & Young LLP, as the independent registered public accounting firm, as described in Proposal No. 2 of the Proxy Statement;

3.	FOR the approval of an amendment to our Amended and Restated Certificate of Incorporation to increase the number of authorized shares of common stock from 300,000,000 shares to 600,000,000 shares, as described in Proposal No. 3 of the Proxy Statement;

TABLE OF CONTENTS

4.	FOR the approval of the amendment to our Amended and Restated 2015 Equity Incentive Plan, as described in Proposal No. 4 of the Proxy Statement;

5.	FOR the approval of the amendment to our Amended and Restated Employee Stock Purchase Plan, as described in Proposal No. 5 of the Proxy Statement;

6.	FOR the advisory vote to approve the compensation of the Company’s named executive officers, as described in Proposal No.6 of the Proxy Statement; and

7.	1 YEAR for the non-binding advisory vote regarding the frequency of future advisory votes by stockholders on the compensation of the Company’s named executive officers, as described in Proposal No. 7 of the Proxy Statement.

Your vote is very important. Whether or not you attend the 2026 Annual Meeting of Stockholders (by logging into www.virtualshareholdermeeting.com/CTMX2026), it is important that your shares be represented. We encourage you to read the accompanying Proxy Statement and our Annual Report on Form 10-K for the year ended December 31, 2025, and submit your proxy on the Internet, by phone or by mail in accordance with the instructions in the Notice of Internet Availability of Proxy Materials. Please review the instructions on the proxy card or the information forwarded by your bank, broker or other holder of record regarding each of these voting options. If you receive more than one set of proxy materials or notice of internet availability because your shares are registered in different names or addresses, each proxy should be signed and submitted to ensure that all of your shares will be voted. Instructions on how to attend the meeting webcast, ask questions or vote your shares online will also be included with the Notice of Internet Availability of Proxy Materials, and are provided in the Proxy Statement accompanying this Notice of Annual Meeting of Stockholders.

On behalf of the Board of Directors, thank you for your participation in this important annual process.


By Order of the Board of Directors
/s/ Christopher W. Ogden
Christopher W. Ogden
Chief Financial Officer and Secretary
South San Francisco, California

April 30, 2026

You are cordially invited to attend the 2026 Annual Meeting of Stockholders by logging into www.virtualshareholdermeeting.com/CTMX2026 and entering the 16-digit control number included in your Notice of Internet Availability of Proxy Materials. Whether or not you expect to attend the 2026 Annual Meeting, please vote on the Internet, by phone or by mail as instructed in the Notice of Internet Availability of Proxy Materials, as promptly as possible in order to ensure your representation at the meeting. Even if you have voted by proxy prior to the meeting, you may still attend the meeting online and submit your vote prior to voting being closed at www.virtualshareholdermeeting.com/CTMX2026. Please note, however, that if your shares of record are held by a broker, bank or other nominee and you wish to vote at the 2026 Annual Meeting, you must obtain a proxy issued in your name from that record holder.

TABLE OF CONTENTS


QUESTIONS AND ANSWERS ABOUT THESE PROXY MATERIALS AND VOTING PROCEDURES			1
PROPOSAL 1: ELECTION OF DIRECTORS			9
PROPOSAL 2: RATIFICATION OF SELECTION OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM			11
PROPOSAL 3: APPROVAL OF AN AMENDMENT TO OUR AMENDED AND RESTATED CERTIFICATE OF INCORPORATION TO INCREASE THE NUMBER OF SHARES OF AUTHORIZED COMMON STOCK FROM 300,000,000 SHARES TO 600,000,000 SHARES			13
PROPOSAL 4: APPROVAL OF THE AMENDMENT TO OUR AMENDED AND RESTATED 2015 EQUITY INCENTIVE PLAN			16
PROPOSAL 5: APPROVAL OF THE AMENDMENT TO OUR AMENDED AND RESTATED EMPLOYEE STOCK PURCHASE PLAN			27
PROPOSAL 6: NON-BINDING, ADVISORY VOTE TO APPROVE THE COMPENSATION OF OUR NAMED EXECUTIVE OFFICERS			32
PROPOSAL 7: ADVISORY VOTE ON THE FREQUENCY OF FUTURE ADVISORY VOTES BY STOCKHOLDERS TO APPROVE THE COMPENSATION OF OUR NAMED EXECUTIVE OFFICERS			33
SECURITY OWNERSHIP OF CERTAIN BENEFICIAL OWNERS AND MANAGEMENT			34
CERTAIN RELATIONSHIPS AND RELATED PARTY TRANSACTIONS			36
BOARD OF DIRECTORS AND CORPORATE GOVERNANCE			37
DIRECTOR COMPENSATION			47
EXECUTIVE OFFICERS			49
EXECUTIVE COMPENSATION			50
EXECUTIVE COMPENSATION TABLES			53
PAY VERSUS PERFORMANCE			56
EQUITY COMPENSATION PLAN INFORMATION			59
REPORT OF THE AUDIT COMMITTEE OF THE BOARD OF DIRECTORS			60
OTHER MATTERS			61
ADDITIONAL INFORMATION			61
Appendix A – Amendment to Amended and Restated Certificate of Incorporation			A-1
Appendix B – Amendment to Amended and Restated 2015 Equity Incentive Plan			B-1
Appendix C – Amendment to Amended and Restated Employee Stock Purchase Plan			C-1

TABLE OF CONTENTS

151 Oyster Point Boulevard, Suite 400

South San Francisco, California 94080

NOTICE OF ANNUAL MEETING OF STOCKHOLDERS

TO BE HELD ON JUNE 17, 2026

AT 1:30 P.M. PACIFIC TIME

QUESTIONS AND ANSWERS ABOUT THESE PROXY MATERIALS AND VOTING PROCEDURES

Why am I receiving these materials?

We sent you a Notice of Internet Availability of Proxy Materials because the board of directors of CytomX Therapeutics, Inc. (the “Board”) is soliciting your proxy to vote at our 2026 Annual Meeting of Stockholders to be held on June 17, 2026 at 1:30 p.m., Pacific Time. The meeting will be held virtually, via a live webcast at www.virtualshareholdermeeting.com/CTMX2026. To attend the live webcast, you will need your unique 16-digit control number provided on the Notice of Internet Availability of Proxy Materials.

We invite you to attend the annual meeting to vote on the proposals described in this Proxy Statement. However, you do not need to attend the meeting to vote your shares. Instead, you may vote by proxy over the Internet or by phone by following the instructions provided in the notice or, if you request printed copies of the proxy materials by mail, you may vote by mail.

Pursuant to the rules adopted by the Securities and Exchange Commission (the “SEC”), we have elected to provide access to our Annual Meeting materials, which include this Proxy Statement and our Annual Report on Form 10-K for the year ended December 31, 2025 (the “Form 10-K”), over the internet in lieu of mailing printed copies. We will begin mailing the Notice of Internet Availability to our stockholders of record as of April 20, 2026 (the “Record Date”) for the first time on or about April 28, 2026. The Notice of Internet Availability will contain instructions on how to access and review the 2026 Annual Meeting materials, how to access the live webcast of the 2026 Annual Meeting of Stockholders, and will also contain instructions on how to request a printed copy of the 2026 Annual Meeting materials. In addition, we have provided brokers, dealers, banks, voting trustees and their nominees, at our expense, with additional copies of our proxy materials and the Form 10-K so that our record-holders can supply these materials to the beneficial owners of shares of our common stock as of the Record Date. The Form 10-K is also available in the “Financial & Filings” section of our website at http://ir.cytomx.com/financial-information/annual-reports.

As used in this Proxy Statement, “CytomX,” the “Company,” “we” or “us” refer to CytomX Therapeutics, Inc., a Delaware corporation.

Who can vote at the annual meeting?

Only stockholders of record at the close of business on April 20, 2026 will be entitled to vote at the annual meeting. On this Record Date, there were 217,702,919 shares of common stock outstanding and entitled to vote.

Stockholder of Record: Shares Registered in Your Name

If, on April 20, 2026, your shares were registered directly in your name with our transfer agent, Computershare Trust Company, N.A., then you are a stockholder of record. The notice will be sent to you by mail and via the Internet directly by us. As a stockholder of record, you may vote online during the live webcast of the meeting at www.virtualshareholdermeeting.com/CTMX2026, or vote by proxy. Whether or not you plan to attend the annual meeting online, we urge you to vote on the Internet or by phone as instructed in the notice or by proxy by mail by requesting a paper copy of the proxy materials as instructed in the notice to ensure your vote is counted.

Beneficial Owner: Shares Registered in the Name of a Broker, Bank or Other Agent

If, on April 20, 2026, your shares were held in an account at a brokerage firm, bank or other agent, then you are the beneficial owner of shares held in “street name” and the notice is being forwarded to you by that organization.

TABLE OF CONTENTS

The organization holding your account is considered the stockholder of record for purposes of voting at the annual meeting. As a beneficial owner, you have the right to direct your broker, bank or other agent on how to vote the shares in your account. Your brokerage firm, bank or other agent will not be able to vote in the election of directors, the amendment to our Amended and Restated 2015 Equity Incentive Plan, the amendment to our Amended and Restated Employee Stock Purchase Plan, the non-binding advisory vote to approve the compensation of our named executive officers and the non-binding advisory vote on the frequency of future advisory votes to approve executive compensation unless they have your voting instructions, so it is very important that you indicate your voting instructions to the institution holding your shares. You are also invited to attend the annual meeting online, as instructed in this Proxy Statement. However, since you are not the stockholder of record, you may not vote your shares online during the annual meeting unless you request and obtain a valid proxy from your broker, bank or other agent.

What am I voting on?

There are seven matters scheduled for a vote:

•	Proposal 1: To elect two directors with terms to expire at the 2029 Annual Meeting of Stockholders.

•	Proposal 2: To ratify the selection of Ernst & Young LLP as our independent registered public accounting firm for our fiscal year ending December 31, 2026.

•	Proposal 3: To approve the amendment to our Amended and Restated Certificate of Incorporation to increase the number of authorized shares of common stock from 300,000,000 shares to 600,000,000 shares

•	Proposal 4: To approve an amendment to increase the number of shares under our Amended and Restated 2015 Equity Incentive Plan.

•	Proposal 5: To approve an amendment to increase the number of shares under our Amended and Restated Employee Stock Purchase Plan.

•	Proposal 6: A non-binding advisory vote to approve the compensation of our named executive officers.

•	Proposal 7: A non-binding advisory vote on the frequency of future advisory votes by stockholders to approve the compensation of our named executive officers.

How are proxy materials distributed?

Under rules adopted by the SEC, we are sending the notice to our stockholders of record and beneficial owners as of April 20, 2026. Stockholders will have the ability to access the proxy materials, including this Proxy Statement and our Annual Report on Form 10-K for the fiscal year ended December 31, 2025, on the Internet at www.proxyvote.com or to request a printed or electronic set of the proxy materials at no charge. Instructions on how to access the proxy materials over the Internet and how to request a printed copy may be found on the notice.

In addition, any stockholder may request to receive proxy materials in printed form by mail or electronically by email on an ongoing basis. Choosing to receive future proxy materials by email will save us the cost of printing and mailing documents to stockholders and will reduce the impact of annual meetings on the environment. A stockholder who chooses to receive future proxy materials by email will receive an email prior to next year’s annual meeting with instructions containing a link to those materials and a link to the proxy voting website. A stockholder’s election to receive proxy materials by email will remain in effect until the stockholder terminates it.

How do I vote?

•	For Proposal 1, you may either vote “For” or “Against” or abstain from voting with respect to each nominee to the Board.

•	For Proposal 2, you may either vote “For” or “Against” or abstain from voting.

•	For Proposal 3, you may either vote “For” or “Against” or abstain from voting.

•	For Proposal 4, you may either vote “For” or “Against” or abstain from voting.

•	For Proposal 5, you may either vote “For” or “Against” or abstain from voting.

•	For Proposal 6, you may either vote “For” or “Against” or abstain from voting.

•	For Proposal 7, you may vote for “1 Year,” “2 Years” or “3 Years” or abstain from voting.

TABLE OF CONTENTS

Please note that by casting your vote by proxy you are authorizing the individuals listed on the Proxy Card to vote your shares in accordance with your instructions and in their discretion with respect to any other matter that properly comes before the annual meeting or any adjournments or postponements thereof.

The procedures for voting are:

Stockholder of Record: Shares Registered in Your Name

If you are a stockholder of record as of April 20, 2026, you may vote by attending the annual meeting online at www.virtualshareholdermeeting.com/CTMX2026 and following the instructions posted on the webcast portal. You may also vote by proxy over the Internet or by phone by following the instructions provided in the Notice of Internet Availability of Proxy Materials or, if you request printed copies of the proxy materials by mail, you may vote by mail. If your proxy is properly executed in time to be voted at the annual meeting, the shares represented by the proxy will be voted in accordance with the instructions you provide. Whether or not you plan to attend the annual meeting online, we urge you to vote by proxy to ensure your vote is counted. You may still attend the annual meeting online and vote online at www.virtualshareholdermeeting.com/CTMX2026 if you have already voted by proxy, so long as you do so before voting closes.

To vote online during the annual meeting, visit www.virtualshareholdermeeting.com/CTMX2026 and have ready your 16-digit control number that was included in your Notice of Internet Availability of Proxy Materials or included in the instructions that accompanied your proxy materials. Shares held in your name as the stockholder of record may be voted electronically during the annual meeting. Shares for which you are the beneficial owner but not the stockholder of record may also be voted electronically during the annual meeting.

To vote on the Internet prior to the annual meeting, go to www.proxyvote.com to complete an electronic proxy card. You will be asked to provide the 16-digit control number from the notice and follow the instructions. Your vote must be received by 11:59 p.m., Eastern Time, on June 16, 2026 to be counted.

3.	To vote by phone, request a paper or email copy of the proxy materials by following the instructions on the notice and call the number provided with the proxy materials to transmit your voting instructions. Your vote must be received by 11:59 p.m., Eastern Time, on June 16, 2026 to be counted.

To vote by mail, request a paper copy of the proxy materials by following the instructions on the notice and complete, sign and date the proxy card enclosed with the paper copy of the proxy materials and return it promptly in the envelope provided. If you return your signed proxy card to us before the annual meeting, we will vote your shares as you direct.

Beneficial Owner: Shares Registered in the Name of a Broker, Bank or Other Agent

If you are a beneficial owner of shares registered in the name of your broker, bank or other agent, you should have received a notice and voting instructions from that organization rather than from us. Simply follow the instructions to ensure that your vote is counted. To vote online at the annual meeting, you must obtain a valid proxy from your broker, bank or other agent. Follow the instructions from your broker, bank or other agent included with the notice, or contact your broker, bank or other agent to request a proxy form.

We provide Internet proxy voting to allow you to vote your shares online, with procedures designed to ensure the authenticity and correctness of your proxy vote instructions. However, please be aware that you must bear any costs associated with your Internet access, such as usage charges from Internet access providers and telephone companies.

How many votes do I have?

On each matter to be voted upon, you have one vote for each share of common stock you owned as of April 20, 2026.

What is the quorum requirement?

A quorum of stockholders is necessary to take any action at the meeting, other than to adjourn the meeting. The presence, online or by proxy duly authorized, of the holders of a majority of the outstanding shares of stock entitled to vote will constitute a quorum. On April 20, 2026, there were 217,702,919 shares of common stock outstanding and entitled to vote.

TABLE OF CONTENTS

Your shares will be counted toward the quorum only if you submit a valid proxy or vote online at the annual meeting. Abstentions and broker non-votes will be counted toward the quorum requirement. If there is no quorum, the chairman of the annual meeting or the holders of a majority of the shares casting votes at the annual meeting may adjourn the annual meeting to another date.

What if I return a proxy card but do not make specific choices?

If you are a stockholder of record and you return a proxy card without marking any voting selections, your shares will be voted as follows:

1.	Proposal 1: “For” the election of two nominees for director.

2.	Proposal 2: “For” the ratification of the Audit Committee’s selection of Ernst & Young LLP as our independent registered public accounting firm for our fiscal year ending December 31, 2026.

3.	Proposal 3: “For” the amendment to our Amended and Restated Certificate of Incorporation to increase the number of authorized shares of common stock from 300,000,000 shares to 600,000,000 shares.

4.	Proposal 4: “For” the approval of the amendment to our Amended and Restated 2015 Equity Incentive Plan.

5.	Proposal 5: “For” the approval of the amendment to our Amended and Restated Employee Stock Purchase Plan.

6.	Proposal 6: “For” the non-binding, advisory vote to approve the compensation of our named executive officers.

7.	Proposal 7: “1 Year” for the non-binding advisory vote regarding the future advisory votes by the stockholders to approve the compensation of our named executive officers.

If any other matter is properly presented at the meeting, your proxy (one of the individuals named on your proxy card) will vote your shares using their best judgment.

If you are a beneficial owner of shares registered in the name of your broker, bank or other agent, your shares are held by your broker, bank or other agent as your nominee, or in “street name,” and you will need to obtain a proxy form from the organization that holds your shares and follow the instructions included on that form regarding how to instruct the organization to vote your shares. If you do not give instructions to your broker, bank or other agent, they can vote your shares with respect to “discretionary” items but not with respect to “non-discretionary” items. Discretionary items are proposals considered routine under the rules of various national securities exchanges, and, in the absence of your voting instructions, your broker, bank or other agent may vote your shares held in street name on such proposals. Non-discretionary items are proposals considered non-routine under the rules of various national securities exchanges, and, in the absence of your voting instructions, your broker, bank or other agent may not vote your shares held in street name on such proposals and the shares will be treated as broker non-votes.

Which ballot measures are considered “routine” or “non-routine”?

Proposal 1 (the election of directors), Proposal 4 (amendment to our Amended and Restated 2015 Equity Incentive Plan), Proposal 5 (amendment to our Amended and Restated Employee Stock Purchase Plan), Proposal 6 (non-binding advisory vote to approve the compensation of our named executive officers) and Proposal 7 (non-binding advisory vote on the frequency of future advisory votes to approve executive compensation) are considered non-routine under applicable rules. A broker or other nominee cannot vote without instructions on non-routine matters, and therefore there may be broker non-votes on Proposals 1, 4, 5, 6 and 7.

Proposal 2 (the ratification of the selection of Ernst & Young LLP as our independent registered public accounting firm for the year ending December 31, 2026) and Proposal 3 (amendment of our Amended and Restated Certificate of Incorporation) are considered routine under applicable rules. A broker or other nominee may generally vote on routine matters, and therefore no broker non-votes are expected to exist in connection with Proposals 2 and 3.

How are votes counted?

Votes will be counted by the inspector of election appointed for the annual meeting, who will count:

•	With respect to Proposals 1, 2, 3, 4, 5 and 6, “For” votes, “Against” votes and abstentions.

•	With respect to Proposal 7, “1 Year,” “2 Years” and “3 Years” votes and abstentions.

•	Additionally, with respect to Proposal 1, 4, 5, 6 and 7, broker non-votes.

TABLE OF CONTENTS

Who will serve as inspector of elections?

Farooq Nomani, our Senior Director and Corporate Counsel, will serve as the inspector of elections.

How many votes are needed to approve each proposal?

•

For Proposal 1, electing two members of the Board, each director must receive a “For” vote from a majority of the votes cast either online or by proxy at the annual meeting and that are entitled to vote on the election of directors. A majority of votes cast shall mean that the number of shares voted “For” the director’s election exceeds 50% of the number of votes cast with respect to that director’s election, with votes cast including votes “Against” in each case and excluding abstentions and broker non-votes with respect to that director’s election.

•

For Proposal 2, ratifying the Audit Committee’s selection of Ernst & Young LLP as our independent registered public accounting firm for our fiscal year ending December 31, 2026, the proposal must receive a “For” vote from the majority of the votes cast either online or by proxy at the annual meeting and that are entitled to vote on the proposal, with votes cast including votes “Against” and excluding abstentions. This is a routine proposal and therefore we do not expect any broker non-votes.

•

For Proposal 3, approving the amendment to our Amended and Restated Certificate of Incorporation to increase the number of authorized shares of common stock from 300,000,000 shares to 600,000,000 shares, the proposal must receive a “For” vote from the majority of the votes cast either online or by proxy at the annual meeting and that are entitled to vote on the proposal, with votes cast including votes “Against” and excluding abstentions. This is a routine proposal and therefore we do not expect any broker non-votes.

•

For Proposal 4, approving the amendment of our Amended and Restated 2015 Equity Inventive Plan, the proposal must receive a “For” vote from the majority of the votes cast either online or by proxy at the annual meeting and that are entitled to vote on the proposal, with votes cast including votes “Against” and excluding abstentions and broker non-votes.

•

For Proposal 5, approving the amendment of our Amended and Restated Employee Stock Purchase Plan, the proposal must receive a “For” vote from the majority of the votes cast either online or by proxy at the annual meeting and that are entitled to vote on the proposal, with votes cast including votes “Against” and excluding abstentions and broker non-votes.

•

For Proposal 6, being the non-binding advisory vote to approve the compensation of our named executive officers, the proposal must receive a “For” vote from the majority of the votes cast either online or by proxy at the annual meeting and that are entitled to vote on the proposal, with votes cast including votes “Against” and excluding abstentions and broker non-votes. While the vote on this resolution is advisory and not binding on us, our Compensation Committee and our Board will consider the outcome of the vote on this resolution when considering future executive compensation decisions.

•

For Proposal 7, being the non-binding advisory vote on the frequency of future advisory votes on executive compensation, the advisory vote frequency alternative (“1 Year”, “2 Years” or “3 Years”) receiving the highest number of “For” votes from the majority of the votes cast either online or by proxy at the annual meeting and entitled to vote on the proposal will be approved, with votes cast excluding abstentions and broker non-votes. If none of the frequency alternatives receives a majority of the votes cast, we will consider the highest number of votes cast by the stockholders to be the frequency that has been selected by the stockholders. However, this proposal is advisory and nonbinding upon us.

Who is paying for this proxy solicitation?

We will pay for the entire cost of soliciting proxies. We have retained Georgeson LLC to assist in the solicitation of proxies for a fee of approximately $15,000 plus associated costs and expenses. In addition to the notice and the proxy materials, our directors and employees may also solicit proxies online, by telephone or by other means of communication. We will not pay our directors and employees any additional compensation for soliciting proxies. We may also reimburse brokerage firms, banks and other agents for the cost of forwarding the notice and any other proxy materials to beneficial owners.

TABLE OF CONTENTS

What does it mean if I receive more than one notice?

If you receive more than one notice, your shares are registered in more than one name or are registered in different accounts. Please vote by proxy according to each notice to ensure that all of your shares are voted.

Can I change my vote after submitting my proxy?

Yes, you can revoke your proxy at any time before the final vote at the annual meeting. If you are a stockholder of record, you may revoke your proxy in any one of three ways:

1.	A duly executed proxy card with a later date or time than the previously submitted proxy;

2.	A written notice that you are revoking your proxy to our Secretary, care of CytomX Therapeutics, Inc., at 151 Oyster Point Boulevard, Suite 400, South San Francisco, CA 94080; or

3.	A later-dated vote on the Internet or by phone or a ballot cast online at the annual meeting by following the instructions at www.virtualshareholdermeeting.com/CTMX2026 (simply attending our virtual annual meeting will not, by itself, revoke your proxy).

If you are a beneficial owner, you may revoke your proxy by submitting new instructions to your broker, bank or other agent, or if you have received a proxy from your broker, bank or other agent giving you the right to vote your shares at the annual meeting, by attending our virtual annual meeting by visiting www.virtualshareholdermeeting.com/CTMX2026 with your 16-digit control number (available in your notice and proxy card) and following the instructions to vote online.

How do I attend the virtual/online annual meeting?

This year’s annual meeting will be held entirely online to support and facilitate stockholder participation. Stockholders of record as of April 20, 2026, will be able to attend and participate in the annual meeting online by accessing www.virtualshareholdermeeting.com/CTMX2026. To join the annual meeting, you will need to have your 16-digit control number, which is included on your Notice of Internet Availability of Proxy Materials and your proxy card.

Even if you plan to attend the annual meeting online, we recommend that you also vote by proxy as described herein so that your vote will be counted if you decide not to attend the annual meeting.

Access to the audio webcast of the annual meeting. The live audio webcast of the annual meeting will begin promptly at 1:30 p.m., Pacific Time on June 17, 2026. Online access to the audio webcast will open approximately thirty minutes prior to the start of the annual meeting to allow time for you to log in and test the computer audio system. We encourage our stockholders to access the annual meeting prior to the start time.

Log in Instructions. To attend the online annual meeting, log in at www.virtualshareholdermeeting.com/CTMX2026. Stockholders will need their unique 16-digit control number, which appears on the Notice of Internet Availability of Proxy Materials and the instructions that accompanied the proxy materials. In the event that you do not have a control number, please contact your broker, bank, or other nominee as soon as possible and no later than May 30, 2026, so that you can be provided with a control number and gain access to the annual meeting.

Submitting questions at the virtual annual meeting. As part of the annual meeting, we will hold a live question and answer session, during which we intend to answer questions submitted during the meeting in accordance with the annual meeting’s rules of conduct that are pertinent to the Company and the meeting matters, as time permits. Questions and answers will be grouped by topic and substantially similar questions will be grouped and answered once. The annual meeting’s rules of conduct will be posted on the Company website approximately 2 weeks prior to the date of the annual meeting.

Technical Assistance. Beginning 30 minutes prior to the start of and during the virtual annual meeting, we will have a support team ready to assist stockholders with any technical difficulties they may have accessing or hearing the virtual meeting.

If you encounter any difficulties accessing the virtual meeting during the check-in or meeting time, you may call our support team at the numbers available on www.virtualshareholdermeeting.com/CTMX2026.

Availability of live webcast to team members and other constituents. The live audio webcast will be available to not only our stockholders but also our team members and other constituents.

TABLE OF CONTENTS

When are stockholder proposals due for next year’s annual meeting?

Pursuant to Rule 14a-8 under the Securities Exchange Act of 1934, as amended (the “Exchange Act”), some stockholder proposals may be eligible for inclusion in our proxy statement for our 2027 Annual Meeting of Stockholders. Any such proposal must be submitted in writing by December 29, 2026, to our Secretary, care of CytomX Therapeutics, Inc., at 151 Oyster Point Boulevard, Suite 400, South San Francisco, CA 94080, the address of our principal executive offices. If we change the date of our 2027 Annual Meeting of Stockholders by more than 30 days from the date of the 2026 Annual Meeting of Stockholders, the deadline shall be a reasonable time before we begin to print and send our proxy materials. Stockholders interested in submitting such a proposal are advised to contact knowledgeable counsel with regard to the detailed requirements of the applicable securities laws and our bylaws. The submission of a stockholder proposal does not guarantee that it will be included in our proxy statement.

Our bylaws also establish an advance notice procedure for stockholders who wish to present a proposal before an annual meeting of stockholders but do not intend for the proposal to be included in our proxy statement. Our bylaws provide that if you wish to submit a proposal that is not to be included in next year’s proxy statement or nominate a director, a timely written notice of a stockholder proposal must be delivered to, or mailed and received by, our Secretary, care of CytomX Therapeutics, Inc., at 151 Oyster Point Boulevard, Suite 400, South San Francisco, CA 94080, no earlier than February 17, 2027 and no later than the close of business on March 19, 2027, which notice must contain the information specified in our bylaws. If we change the date of our 2027 Annual Meeting of Stockholders by more than 30 days before, or more than 60 days after, the one-year anniversary of the 2026 Annual Meeting of Stockholders, then the written notice of a stockholder proposal that is not intended to be included in our proxy statement must be delivered, or mailed and received, not later than the 90^th day prior to our 2027 Annual Meeting of Stockholders or, if later, the 10^th day following the day on which certain public disclosure as described in our bylaws of the meeting date is made.

In addition to satisfying the foregoing requirements under our current bylaws, stockholders who intend to solicit proxies in support of director nominees other than the Company’s nominees for our annual meeting to be held in 2027 must provide notice that sets forth the information required by Rule 14a-19 under the Exchange Act no later than 5:00 p.m., Eastern Time, on April 18, 2027, including providing a statement that such stockholder intends to solicit the holders of shares representing at least 67% of the voting power of the Company’s shares entitled to vote on the election of directors in support of director nominees other than the Company’s nominees. If our 2027 annual meeting is changed by more than 30 calendar days from the first anniversary of our 2026 annual meeting, stockholders must comply with the additional requirements of Rule 14a-19(b) under the Exchange Act no later than the later of 60 calendar days prior to the date of the 2027 annual meeting or the 10^th calendar day following the day on which public announcement of the date of the 2027 annual meeting is first made.

We intend to file a proxy statement and WHITE proxy card with the SEC in connection with our solicitation of proxies for our 2027 Annual Meeting of Stockholders. Stockholders may obtain our proxy statement (and any amendments and supplements thereto) and other documents for our 2027 Annual Meeting of Stockholders as and when filed by us with the SEC without charge from the SEC’s website at: www.sec.gov.

What is “householding” and how does it affect me?

We have adopted a procedure approved by the SEC called “householding.” Under this procedure, stockholders who have the same address may receive only one copy of our annual report, proxy statement or Notice of Internet Availability of Proxy Materials, unless one or more of these stockholders notifies us that they wish to receive individual copies of such documents. This process potentially means extra convenience for stockholders and cost savings for companies.

If you are a beneficial owner of our common stock, once you receive notice from your broker, bank or other agent that they will be householding communications to your address, householding will continue until you are notified otherwise or until you revoke your consent. If, at any time, you no longer wish to participate in householding and would prefer to receive separate copies of our annual report, proxy statement or Notice of Internet Availability of Proxy Materials, please notify your broker, bank or other agent, and direct your written request to CytomX Therapeutics, Inc., Secretary, at 151 Oyster Point Boulevard, Suite 400, South San Francisco, CA 94080 or contact our Secretary at (650) 515-3185. Upon written or oral request to us, we will promptly deliver a separate copy of the annual report to security holders, proxy statement, or Notice of Internet Availability of Proxy Materials, as applicable, to a security

TABLE OF CONTENTS

holder at a shared address to which a single copy of the documents was delivered. Stockholders who currently receive multiple copies of our annual report, proxy statement or Notice of Internet Availability of Proxy Materials at their address and would like to request householding of their communications should contact their broker, bank or other agent.

How can I find out the results of the voting at the annual meeting?

Preliminary voting results will be announced during the live webcast of the annual meeting. Final voting results will be published in a Current Report on Form 8-K filed with the SEC within four business days following the annual meeting.

TABLE OF CONTENTS

PROPOSAL 1: ELECTION OF DIRECTORS

Our Board currently consists of eight directors and is divided into three classes, designated as Class I, Class II and Class III. Under our Amended and Restated Certificate of Incorporation, our Board is authorized to assign its members in office to each class and each class has a term of three years. There are currently two directors in Class II, Matthew P. Young, and Elaine V. Jones Ph.D., whose terms of office are scheduled to expire at the 2026 Annual Meeting of Stockholders. Both, Mr. Young and Dr. Jones have been nominated for election at the 2026 Annual Meeting of Stockholders.

Any vacancies on our Board resulting from death, resignation, disqualification, removal or other causes, and any newly created directorships resulting from any increase in the number of directors, shall be filled by the affirmative vote of a majority of the directors then in office, even though less than a quorum of the Board. Any director elected to fill a vacancy shall hold office for the remainder of the unexpired term in which the vacancy occurred or newly created directorship was created and until such director’s successor shall have been elected and qualified.

Directors are elected by a majority of the votes cast at the annual meeting and entitled to vote on the election of directors. A majority of votes cast shall mean that the number of shares voted “For” a director’s election exceeds 50% of the number of votes cast with respect to that director’s election, with votes cast including votes “Against” in each case and excluding abstentions and broker non-votes with respect to that director’s election. Shares represented by executed proxies will be voted for the election of the nominees named below, unless the “Against” or “Abstain” voting selection has been marked on the proxy card.

If either of Mr. Young or Dr. Jones become unavailable for election as a result of an unexpected occurrence, shares that would otherwise be voted for such director will be voted for the election of a substitute nominee proposed by the Nominating and Corporate Governance Committee and nominated by the Board. Mr. Young and Dr. Jones have agreed to serve if elected. Our management has no reason to believe that either Mr. Young or Dr. Jones will be unable to serve. If elected at the annual meeting, both Mr. Young and Dr. Jones will serve until the earliest of the 2029 Annual Meeting of Stockholders, or their respective successor is elected and qualified, or until their respective death, resignation or removal.

The following are brief biographies of Mr. Young and Dr. Jones, the nominees for director, and a discussion of their specific experience, qualifications, attributes or skills that led the Nominating and Corporate Governance Committee of the Board to recommend each of them for director, as of the date of this proxy statement.

Mr. Matthew P. Young has served as a member of our Board since September 2015. Mr. Young currently serves as a Managing Director at Longitude Capital, a position he has held since August 2022. Before that, Mr. Young was serving as Chief Operating Officer and Chief Financial Officer of GRAIL from October 2019 to December 2021. Prior to joining GRAIL, Mr. Young had served as Executive Vice President and Chief Financial Officer of Jazz Pharmaceuticals (“Jazz”), a role he held since February 2015. He previously had served as Senior Vice President and Chief Financial Officer of Jazz since March 2014 and as Senior Vice President, Corporate Development of Jazz since April 2013. Prior to joining Jazz, Mr. Young worked in investment banking for approximately 20 years. From February 2009 to April 2013, he served as a Managing Director in global healthcare of Barclays Capital Inc., an investment banking firm, where his role included acting as the co-head of life sciences at Barclays Capital. From 2007 to 2008, Mr. Young served as a Managing Director of Citigroup Global Markets Inc., an investment banking firm, and, from 2003 to 2007, as a Managing Director of Lehman Brothers Inc., an investment banking firm. In 2015, he joined the board of directors of PRA Health Sciences Inc., a contract research company, a position he held until July 2021. Mr. Young currently serves on the board of directors of the privately-held biopharmaceutical companies OrsoBio, Inc., Alpha-9 Oncology, Inc. and AllIn Bio. Mr. Young received a B.S. in economics and a M.B.A. from the Wharton School of the University of Pennsylvania. We believe that Mr. Young is qualified to serve on our Board due to his extensive management experience, significant experience in the life sciences industry and financial expertise.

Elaine V. Jones, Ph.D., has served as a member of our Board since May 2019. Dr. Jones retired in April 2019 from her role as Vice President, Worldwide Business Development and Senior Partner at Pfizer Ventures, the venture capital arm of Pfizer Inc. After joining Pfizer Ventures as Executive Director in 2008, Dr. Jones was responsible for making and managing venture investments for Pfizer as well as serving in board roles for several therapeutic companies. Prior to

TABLE OF CONTENTS

this, Dr. Jones held the position of General Partner at EuclidSR Partners, a venture firm specializing in private investment in private and public equity within the health sciences, healthcare, biopharmaceutical sectors, until 2008. Dr. Jones began her investment career at S.R. One, the corporate investment fund of GlaxoSmithKline, which she joined in 1999. Prior to this, Dr. Jones served as Director of Scientific Licensing at SmithKline Beecham and as a research scientist in the research and development division of SmithKline Beecham Pharmaceutical. During her venture career, Dr. Jones has served on the boards of more than 20 early to mid-stage biotechnology, therapeutic and pharmaceutical companies. She has served on the board of HBM Healthcare Investments AG, a publicly-traded Swiss Investment Company since June 2018. She has also served on the board of NextCure, Inc., a publicly-traded biopharmaceutical company, since December 2015. Dr. Jones also currently serves on the boards of privately held biopharmaceutical companies and has served on the board of the Novartis Venture Fund since 2020. Dr. Jones previously served as a member of the board of directors of Gritstone Oncology, a publicly-traded biopharmaceutical company, from September 2019 to April 2025. Dr. Jones holds a B.S. in biology from Juniata College and a Ph.D. in microbiology from the University of Pittsburgh. We believe that Dr. Jones is qualified to serve on our Board due to her broad knowledge of the life sciences industry and significant experience in pharmaceutical drug discovery and business development.

THE BOARD OF DIRECTORS RECOMMENDS A VOTE “FOR” THE ELECTION OF EACH OF THE NAMED NOMINEES.

TABLE OF CONTENTS

PROPOSAL 2: RATIFICATION OF SELECTION OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

The Audit Committee of our Board has selected Ernst & Young LLP as our independent registered public accounting firm for the fiscal year ending December 31, 2026, and has further directed that management submit the selection of our independent registered public accounting firm for ratification by the stockholders at the annual meeting. Ernst & Young LLP has audited our financial statements for each of our fiscal years since the fiscal year ended December 31, 2017. Representatives of Ernst & Young LLP are expected to be present at the virtual annual meeting. During the webcast, they will have an opportunity to make a statement if they so desire and will be available to respond to appropriate questions submitted online.

Neither our bylaws nor other governing documents or law require stockholder ratification of the selection of Ernst & Young LLP as our independent registered public accounting firm. However, the Audit Committee is submitting the selection of Ernst & Young LLP to the stockholders for ratification as a matter of good corporate practice. If the stockholders fail to ratify the selection, the Audit Committee will reconsider whether or not to retain Ernst & Young LLP. Even if the selection is ratified, the Audit Committee, in its discretion, may direct the appointment of a different independent registered public accounting firm at any time during the year if the Audit Committee determines that such a change would be in our best interests and our stockholders’ best interest.

The affirmative vote of the holders of a majority of the votes cast either online or by proxy at the annual meeting and that are entitled to vote on this proposal will be required to ratify the selection of Ernst & Young LLP for our fiscal year ending December 31, 2026, with votes cast including votes “Against” and excluding abstentions. Abstentions will not be counted as votes cast and will have no effect on the outcome of this proposal. This is a routine proposal and therefore no broker non-votes are expected to exist in connection with this proposal.

Independent registered public accounting firm fees and services

The following table provides information regarding the approximate fees billed by Ernst & Young LLP during the years ended December 31, 2025 and 2024. The Audit Committee approved all of the fees described below.


	Year Ended December 31,
	2025 $	2024 $
Audit Fees⁽¹⁾	1,852,050	1,806,100
Tax Fees⁽²⁾	75,718	73,583
Audit-Related Fees⁽³⁾	—	—
All Other Fees	—	—
Total Fees	1,927,768	1,879,683

(1)

Audit fees of Ernst & Young LLP for the years ended December 31, 2025 and 2024 were for professional services rendered for the audits of our financial statements, including accounting consultation, reviews of quarterly financial statements and professional services rendered in connection with our registration statements.

(2)	This category consists of fees for services provided for tax consultation and compliance services.

(3)	This category consists of fees for professional services rendered that are reasonably related to the performance of the audit or review of our financial statements.

Pre-Approval Policies and Procedures

The Audit Committee has adopted policies and procedures for the pre-approval of audit and non-audit services provided by our independent registered public accounting firm, Ernst & Young LLP. The policy generally requires pre-approval for specified services in the defined categories of audit services, audit-related services and tax services up to specified amounts. Pre-approval may also be given as part of the Audit Committee’s approval of the scope of the engagement of the independent registered public accounting firm or on an individual explicit case-by-case basis before the independent registered public accounting firm is engaged to provide each service. The pre-approval of services may be delegated to one or more of the Audit Committee’s members, but the decision must be reported to the full Audit Committee at its next scheduled meeting.

TABLE OF CONTENTS

The Audit Committee will review both audit and non-audit services performed by Ernst & Young LLP and the fees charged for such services on at least an annual basis. Among other things, the Audit Committee will review non-audit services proposed to be provided by Ernst & Young LLP and pre-approve such services only if they are compatible with maintaining Ernst & Young LLP’s status as an independent registered public accounting firm. All services provided by Ernst & Young LLP in 2025 and 2024 were pre-approved by our Board or the Audit Committee after review of each of the services proposed for approval.

THE BOARD OF DIRECTORS RECOMMENDS A VOTE “FOR” THE RATIFICATION OF THE SELECTION OF ERNST & YOUNG LLP AS OUR INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM FOR THE FISCAL YEAR ENDING DECEMBER 31, 2026.

TABLE OF CONTENTS

PROPOSAL 3: APPROVAL OF AN AMENDMENT TO OUR AMENDED AND RESTATED CERTIFICATE OF INCORPORATION TO INCREASE THE NUMBER OF SHARES OF AUTHORIZED COMMON STOCK FROM 300,000,000 TO 600,000,000

Summary

We are asking our stockholders to approve an amendment to Article Four, Section A of our Amended and Restated Certificate of Incorporation to increase the total number of authorized shares of common stock, par value $0.00001 per share, from 300,000,000 shares to 600,000,000 shares (the “Charter Amendment”). The Charter Amendment will not change the number of authorized shares of preferred stock, which will remain at 10,000,000 shares. If approved, the total number of shares of all classes of capital stock that the Company is authorized to issue will increase from 310,000,000 shares to 610,000,000 shares.

Current Utilization of Authorized Shares

The following table sets forth, as of March 31, 2026, information regarding our authorized, issued and outstanding, reserved, and available shares of common stock:


			Shares
Authorized shares of common stock			300,000,000
Shares of common stock issued and outstanding			217,693,878
Shares issuable upon exercise of outstanding stock options, having a weighted average exercise price of $5.15 per share			18,876,388
Shares issuable upon vesting and settlement of outstanding restricted stock units and performance stock units			3,413,313
Shares reserved for future issuance under our Amended and Restated 2015 Equity Incentive Plan			1,711,325
Shares reserved for future issuance under our Amended and Restated Employee Stock Purchase Plan			348,824
Shares issuable upon exercise of pre-funded warrants issued in the March 2026 offering			1,179,245
Shares issuable upon exercise of Tranche Warrants (exercise price of $3.77 per share)			5,769,231
Total shares issued, outstanding, and reserved			248,992,204
Authorized shares of common stock available for future issuance			82,306,122

As of March 31, 2026, 82,306,122 shares of authorized common stock remained available for future issuance. The Charter Amendment will not change the number of authorized shares of preferred stock. As of March 31, 2026, 10,000,000

Matthew P. Young

Class II Director

Elaine V. Jones Ph.D.

Class II Director

SEC Form DEF 14A filed by CytomX Therapeutics Inc.