CytomX Therapeutics (CTMX) 8-K Changes in Registrant's Certifying Accountant

EXHIBIT 16.1

July 17, 2017

Securities and Exchange Commission

100 F Street, N.E.

Washington, DC 20549

Commissioners:

We have read the statements made by CytomX Therapeutics, Inc. (copy attached), which we understand will be filed with the Securities and Exchange Commission, pursuant to Item 4.01 of Form 8-K, as part of the Form 8-K of CytomX Therapeutics, Inc. dated July 12, 2017. We agree with the statements concerning our Firm in such Form 8-K.

Very truly yours,

/s/ PricewaterhouseCoopers LLP

San Jose, CA