CytomX Therapeutics Provides Update on CX-2051 Phase 1 Study

- The CTMX-2051-101 study has enrolled 73 colorectal cancer patients to-date, aligned with the Company’s goal of providing a Phase 1 data update in Q1 2026 -

- The CTMX-2051-101 study remains active and patients continue to be dosed with CX-2051 across all expansion doses -

SOUTH SAN FRANCISCO, Calif., Aug. 13, 2025 (GLOBE NEWSWIRE) -- CytomX Therapeutics, Inc. (Nasdaq: CTMX), a leader in the field of masked, conditionally activated biologics, today provided an update on the CX-2051 Phase 1 study to address certain recent social media posts.

“Since our initial data disclosure in May 2025, Phase 1 enrollment has been rapid and is substantially complete. We are on track to provide a data update in the first quarter of 2026. Patient safety remains our top priority as we continue to advance CX-2051 for the treatment of CRC,” said Sean McCarthy, D.Phil., chief executive officer and chairman of CytomX.

CX-2051 Program Status:

• CX-2051 dose expansions at 7.2 mg/kg, 8.6 mg/kg, and 10 mg/kg doses, administered every three weeks (Q3W) have each enrolled approximately 20 patients as planned.
• A single Grade 5 treatment-related acute kidney injury occured in a patient with a complex medical history including having a solitary kidney. The Grade 5 event was believed to be secondary to nausea, vomiting and diarrhea. The Company was made aware of the event on July 11, 2025 and promptly reported the event to the FDA on July 18, 2025 in accordance with regulatory requirements.
• The CTMX-2051-101 Safety Review Committee convened on July 14, 2025 and supported continued study execution and enrollment.
• The CTMX-2051-101 study is ongoing. A Phase 1 data update is expected by Q1 2026.

About CytomX Therapeutics
CytomX is a clinical-stage, oncology-focused biopharmaceutical company focused on developing novel conditionally activated, masked biologics designed to be localized to the tumor microenvironment. By pioneering a novel pipeline of localized biologics, powered by its PROBODY ^® therapeutic platform, CytomX’s vision is to create safer, more effective therapies for the treatment of cancer. CytomX’s multi-modality technology platform has produced therapeutic candidates across multiple treatment modalities including antibody-drug conjugates (ADCs), T-cell engagers, and immune modulators such as cytokines. CytomX’s current clinical-stage pipeline includes CX-2051 and CX-801. CX-2051 is a masked, conditionally activated ADC directed toward epithelial cell adhesion molecule (EpCAM), armed with a topoisomerase-1 inhibitor payload. CX-2051 has potential applicability across multiple EpCAM-expressing epithelial cancers, including CRC, and was discovered in collaboration with ImmunoGen. CX-801 is a masked interferon alpha-2b PROBODY ^® cytokine with broad potential applicability in traditionally immuno-oncology sensitive as well as insensitive (cold) tumors. CytomX has established strategic collaborations with multiple leaders in oncology, including Amgen, Astellas, Bristol Myers Squibb, Regeneron and Moderna. For more information about CytomX and how it is working to make conditionally activated treatments the new standard-of-care in the fight against cancer, visit www.cytomx.com and follow us on LinkedIn and X (formerly Twitter) .

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, including those related to CX-2051. Accordingly, you should not rely on any of these forward-looking statements, including those relating to the potential benefits, safety and efficacy or progress of CytomX’s or any of its collaborative partners’ product candidates, including CX-2051 and CX-801, the potential benefits or applications of CytomX’s PROBODY ^® therapeutic platform, CytomX’s or its collaborative partners’ ability to develop and advance product candidates into and successfully complete clinical trials, including the ongoing and planned clinical trials of CX-2051 and CX-801 and the timing of initial and ongoing data availability for our clinical trials, including CX-2051 and CX-801, and other development milestones. Risks and uncertainties that contribute to the uncertain nature of the forward-looking statements include: the unproven nature of CytomX’s novel PROBODY ^® therapeutic technology; uncertainties around the Company’s ability to raise sufficient funds to carry out its planned research and development; CytomX’s clinical trial product candidates 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, including the possibility that the results of preclinical research and early clinical trials, including initial CX-2051 results, may not be predictive of future results; the possibility that CytomX’s clinical trials will not be successful; the possibility that current preclinical research may not result in additional product candidates; CytomX’s dependence on the success of CX-2051 and CX-801; CytomX’s reliance on third parties for the manufacture of the Company’s product candidates; possible regulatory developments in the United States and foreign countries, including China and the European Union; and the risk that we may incur higher costs than expected for research and development or unexpected costs and expenses. 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 August 7, 2025. 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.

PROBODY is a U.S. registered trademark of CytomX Therapeutics, Inc. All other trademarks are the properties of their respective owners.

Company Contact:
Chris Ogden
SVP, Chief Financial Officer
cogden@cytomx.com

Investor Contact:
Precision AQ (formerly Stern Investor Relations)
Stephanie Ascher
Stephanie.Ascher@precisionaq.com

Media Contact:
Redhouse Communications
Teri Dahlman
teri@redhousecomms.com