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CytomX Therapeutics Presents CX-072 Clinical Translational Data at 2018 SITC Annual Meeting

November 9, 2018

- Demonstrates Further Proof-of-Mechanism of Probody™ Platform –

- Consistent with CX-072 Clinical Observations at 2018 ASCO and ESMO Presentations-

- Company to Host Analyst and Investor Event and Webcast Tomorrow, Saturday, November 10th -

SOUTH SAN FRANCISCO, Calif., Nov. 09, 2018 (GLOBE NEWSWIRE) -- CytomX Therapeutics, Inc. (Nasdaq: CTMX), a clinical-stage oncology-focused biopharmaceutical company pioneering a novel class of investigational antibody therapeutics based on its Probody™ therapeutic technology platform, today announced that clinical translational data from PROCLAIM-072, an ongoing Phase 1/2 trial evaluating CX-072, a Probody therapeutic targeting PD-L1, was presented as a poster this morning and will be highlighted during a rapid fire oral presentation tomorrow at the 33rd Annual Meeting of The Society for Immunotherapy of Cancer (SITC) being held in Washington DC.

“These preliminary data provide additional proof-of concept for the Probody platform and build upon the clinical data we have presented to date showing that CX-072 appears to be performing as designed in patients,” said W. Michael Kavanaugh, M.D. chief scientific officer and head of research and non-clinical development at CytomX. “These findings confirm that CX-072 is unmasked and activated and has biological activity in patient tumors while remaining predominantly masked and intact in circulation. This is another important step in understanding the full potential of our novel platform.”

Poster P87: Preliminary Evidence of Intratumoral Activation and Immunomodulatory Effect of CX-072, a Probody Therapeutic Antibody Prodrug Targeting PD-L1, in a Phase 1/2a Trial

The primary objective of this translational study is to investigate the molecular mechanism of the Probody therapeutic CX-072 in cancer patients. Patients received escalating doses of CX-072 from 0.3 mg/kg to 30 mg/kg. Biopsies were obtained from a subset of PROCLAIM-CX-072 patients during screening and at either 3-5 days after the first dose or after 4-6 weeks of CX-072 therapy. The presence of protease activity, CX-072 cleavage and activation, and measures of biological activity were assessed within tumors.

Results showed that protease activity was detected in the majority of patient biopsy samples (15 of 18 (83%)). Further, CX-072 was cleaved and activated within tumors, with the total amount of activated CX-072 increasing with dose. Doses of ≥ 3 mg/kg of CX-072 were estimated to achieve ≥ 98% PD-L1 target occupancy in patient tumors and attained concentrations that are associated with efficacy in a preclinical model. 7 of 12 evaluable patient biopsies showed an increase in tumor infiltration of CD8+ T cells, an activity consistent with the inhibition of the PD-1/PD-L1 signaling pathway.

These data have been selected for presentation as part of SITC’s Rapid Oral Abstracts Session. The presentation, Preliminary Evidence of Intratumoral Activation and Immunomodulatory Effect of CX-072, a Probody Therapeutic Antibody Prodrug Targeting PD-L1, in a Phase 1/2a Trial, will be made by Luc Desnoyers, Ph.D., senior director of translational sciences at CytomX Therapeutics on Saturday, November 10, 2018 at 1:05pm EST.

Analyst and Investor Event and Webcast

CytomX will host an analyst event, conference call and live webcast with slides tomorrow, Saturday, November 10, 2018, beginning at 12:30 p.m. EST/ 9:30 a.m. PST to discuss the SITC data presentation. This event can be accessed in three ways:

-- From the CytomX website: http://ir.cytomx.com/events-and-presentations. Please access the website 15 minutes prior to the start of the call to download and install any necessary audio software and slides. -- By telephone: Participants can access the call by dialing 1-877-809-6037 (United States) or 1- 615-247-0221 (International) referencing Conference ID 4597498. -- By replay: A replay of the webcast will be located under the Investor Relations section of CytomX’s website approximately two hours after the conclusion of the live call and will be available for 30 days following the call.

About PROCLAIM

PROCLAIM (Probody Clinical Assessment In Man) is an international umbrella program designed to evaluate CytomX’s Probody therapeutics. The first module is the PROCLAIM-CX-072 clinical program, an open-label, dose-finding Phase 1/2 trial evaluating CX-072 as monotherapy and in combination with Yervoy® (ipilimumab) or Zelboraf®(vemurafenib) in patients with metastatic or locally advanced unresectable solid tumors or lymphomas. CytomX aims to achieve three goals as part of the PROCLAIM-072 clinical trial:

-- Tolerability: Demonstrate that CX-072 is well tolerated in patients and potentially improves safety, particularly in the combination setting. -- Anti-cancer activity: Demonstrate initial evidence of CX-072’s anti-cancer activity as monotherapy and in combination. -- Translational program and Probody platform proof-of-concept: Explore mechanistic aspects of Probody activity in patients as observed in preclinical models.

About CytomX Therapeutics

CytomX Therapeutics is a clinical-stage oncology-focused biopharmaceutical company pioneering a novel class of investigational antibody therapeutics based on its Probody™ therapeutic technology platform. Probody therapeutics are designed to exploit unique conditions of the tumor microenvironment to more effectively localize antibody binding and activity while limiting activity in healthy tissues. CytomX and its partners have four programs in the clinic. The Company’s pipeline includes cancer immunotherapies against clinically-validated targets, including a PD-L1-targeting Probody therapeutic wholly owned by CytomX (CX-072), a PD-1-targeting Probody therapeutic wholly owned by CytomX (CX-188) and a CTLA-4-targeting Probody therapeutic partnered with Bristol Myers Squibb (BMS-986249). The pipeline also includes first-in-class Probody drug conjugates against highly attractive targets including a CD166-targeting Probody drug conjugate wholly owned by CytomX (CX-2009), and a CD71-targeting Probody drug conjugate partnered with AbbVie (CX-2029). CD166 and CD71 are among cancer targets that are considered to be inaccessible to conventional antibody drug conjugates due to their presence on many healthy tissues. In addition to its wholly owned programs, CytomX has strategic collaborations with AbbVie, Amgen, Bristol-Myers Squibb Company and ImmunoGen, Inc. For more information, visit www.cytomx.com.

CytomX Therapeutics Forward-Looking Statements

This press release includes forward-looking statements. Such forward-looking statements involve known and unknown risks, uncertainties and other important factors that are difficult to predict, may be beyond our control, and may cause the actual results, performance or achievements to be materially different from any future results, performance or achievements expressed or implied in such statements. Accordingly, you should not rely on any of these forward-looking statements, including those relating to the potential benefits, safety and efficacy of CytomX’s or any of its collaborative partners’ product candidates, administered separately or in combination, CytomX’s ability and the ability of its collaborative partners to develop and advance product candidates into and successfully complete clinical trials, including CytomX’s Phase 1/2 clinical trials of CX-072, CX-2009 and CX-2029, the timing of any future clinical trials to be initiated by CytomX or any of its collaborative partners, including a clinical trial for CX-188, CytomX’s expectations regarding the availability of clinical data, including data from the ongoing clinical trial of CX-2009, CytomX’s expectations with respect to its collaborations, and CytomX’s expectations regarding the timing of potential regulatory filings. Risks and uncertainties that contribute to the uncertain nature of the forward-looking statements include: three of CytomX’s product candidates under its Probody platform are in the initial stages of clinical development and its other product candidates are currently in preclinical development, and the process by which preclinical and clinical development could potentially lead to an approved product is long and subject to significant risks and uncertainties; the possibility that the results of early clinical trials may not be predictive of future results; the possibility that CytomX’s clinical trials will not be successful; CytomX’s dependence on the success of CX-072, CX-2009 and CX-2029; CytomX’s reliance on third parties for the manufacture of the company’s product candidates; and possible regulatory developments in the United States and foreign countries. Projected net cash utilization and capital resources are subject to substantial risk of variance based on a wide variety of factors that can be difficult to predict. Additional applicable risks and uncertainties include those relating to our preclinical research and development, clinical development, and other risks identified under the heading “Risk Factors” included in CytomX’s Quarterly Report on Form 10-Q filed with the SEC on November 6, 2018. The forward-looking statements contained in this press release are based on information currently available to CytomX and speak only as of the date on which they are made. CytomX does not undertake and specifically disclaims any obligation to update any forward-looking statements, whether as a result of any new information, future events, changed circumstances or otherwise.

Contact:

Investors and Media:

Christopher Keenan VP, Investor Relations and Corporate Communications ckeenan@cytomx.com 650-383-0823

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