CytomX Reports Patient Death in Phase I Colorectal Cancer Trial, Continues Development of CX-2051

Trial Continues Despite Setback

CytomX Therapeutics has reported a treatment-related patient death in its Phase I clinical trial for CX-2051, an investigational antibody-drug conjugate (ADC) being tested for colorectal cancer. The California-based biotech disclosed that the mortality was linked to acute kidney injury in a patient with a complex medical history and only one remaining kidney.

The company learned of the death on July 11 and promptly reported the event to the FDA on July 18, in accordance with regulatory requirements. Despite this setback, the safety review board for the Phase I study convened shortly after the incident and endorsed the continuation of the trial.

CX-2051: Promising Results Amid Safety Concerns

CX-2051 is designed to target the epithelial cell adhesion molecule (EpCAM) and is being developed as a conditionally activated ADC with potential applicability across various EpCAM-expressing cancers. In May, CytomX released interim data for the drug, showing promising results in advanced colorectal cancer patients.

Out of 18 evaluated patients, five achieved confirmed partial response, resulting in a 28% overall response rate. At the highest dose level of 10 mg/kg, the response rate increased to 43%. The disease control rate was an impressive 94% across all dose arms.

While these results are encouraging, the recent patient death highlights the potential risks associated with the treatment. Prior to this incident, CytomX had reported that CX-2051 was "generally well-tolerated with manageable adverse events" and had no dose-limiting toxicities. However, there were five cases of grade 3 diarrhea and one of nausea reported in earlier data.

Financial Outlook and Future Plans

As of June 30, CytomX reported $158.1 million in cash, cash equivalents, and investments, which the company expects will sustain operations into the second quarter of 2027. This financial cushion comes after a significant restructuring in January, when the biotech reduced its workforce by 40%, laying off approximately 48 employees to focus resources on the development of CX-2051.

Looking ahead, CytomX anticipates releasing further data from the Phase I trial in the first quarter of 2026. The company is also planning to initiate a Phase II study for CX-2051 in advanced late-line colorectal cancer in the first half of 2026. Additionally, CytomX is exploring the potential for combination studies in earlier lines of colorectal cancer treatment and a Phase Ib study to assess the drug's efficacy in other solid tumors.