CytomX Announces Closing of Initial Public Offering and Full Exercise of Underwriters Option to Purchase Additional Shares

CytomX Announces Closing of Initial Public Offering and

Full Exercise of Underwriters Option to Purchase Additional Shares

SOUTH SAN FRANCISCO, Calif., October 14, 2015 CytomX Therapeutics, Inc. (Nasdaq: CTMX) (the Company ), a biopharmaceutical

company developing Probody therapeutics for the treatment of cancer, today announced the closing of its initial public offering of 7,666,667 shares of common stock at an initial public offering price of $12.00 per share, before underwriting

discounts and commissions, which includes the exercise in full by the underwriters of their option to purchase up to 1,000,000 additional shares of common stock. The Company s common stock began trading on The NASDAQ Global Select Market on

October 8, 2015, under the ticker symbol CTMX.

BofA Merrill Lynch, Jefferies LLC and Cowen and Company LLC acted as joint book-running

managers for the offering. Oppenheimer & Co. served as manager for the offering.

A registration statement relating to the securities being sold

in the offering was declared effective by the Securities and Exchange Commission on October 7, 2015. The offering was made solely by means of a prospectus, copies of which may be obtained from BofA Merrill Lynch, 222 Broadway, New York, NY

10038, Attention: Prospectus Department, or by email at dg.prospectus_requests@baml.com; Jefferies LLC, Equity Syndicate Prospectus Department, 520 Madison Avenue, 2nd Floor, New York, NY 10022, by telephone at (877) 821-7388 or by

email at Prospectus_Department@Jefferies.com; or Cowen and Company, LLC, c/o Broadridge Financial Services, Attention: Prospectus Department, 1155 Long Island Avenue, Edgewood, NY 11717, by telephone at 631-274-2806 or by fax at

This press release shall not constitute an offer to sell or a solicitation of an offer to buy, nor shall there be any sale of these

securities in any state or jurisdiction in which such offer, solicitation or sale would be unlawful, prior to registration or qualification under the securities laws of any such state or jurisdiction.

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