CytomX Reports Patient Death in Phase I Colorectal Cancer Trial, Continues Study Development

Treatment-Related Mortality Linked to Acute Kidney Injury

CytomX Therapeutics has disclosed a patient death in its ongoing Phase I trial for CX-2051, an investigational antibody-drug conjugate (ADC) targeting colorectal cancer. The California-based biotech announced on Wednesday that the mortality was associated with acute kidney injury in a patient with a complex medical history, including having only one kidney.

The company learned of the death on July 11 and promptly reported the event to the FDA on July 18, adhering to 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 applications across various EpCAM-expressing cancers. The ongoing early-stage program focuses on solid tumors, with a particular emphasis on advanced colorectal cancer.

Interim data released by CytomX in May showed encouraging results, with a 28% overall response rate among 18 evaluated patients. At the highest dose level of 10 mg/kg, 43% of treated patients achieved confirmed partial response. The disease control rate was reported at an impressive 94% across all dose arms.

However, the trial has not been without its challenges. While CytomX initially reported that CX-2051 was "generally well-tolerated with manageable adverse events" and no dose-limiting toxicities, they also noted five cases of grade 3 diarrhea and one case of nausea.

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, where the biotech reduced its workforce by 40%, laying off approximately 48 employees to focus resources on CX-2051 development.

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 ADC's efficacy in other solid tumors.

The news of the patient death has impacted CytomX's stock, with shares dropping as much as 14% to $1.78 at the close of trading on Wednesday. Despite this setback, the company remains committed to the development of CX-2051 and its broader oncology pipeline.