CytomX Therapeutics Reports Patient Death in ADC Trial, Continues Study

CytomX Therapeutics, a biotechnology company focusing on antibody-drug conjugates (ADCs), has reported a patient death in its ongoing phase 1 trial of CX-2051, its lead ADC candidate for metastatic colorectal cancer (CRC). Despite this setback, the company has been advised to continue the study, highlighting the complex landscape of clinical trials in oncology.

Trial Details and Patient Fatality

The phase 1 study of CX-2051 has enrolled 73 patients to date, with approximately 20 patients entering the dose expansion portion. Patients in this phase receive either 7.2-mg/kg, 8.6-mg/kg, or 10-mg/kg doses of CX-2051 every three weeks. The fatality occurred in one of these patients, who experienced a treatment-related acute kidney injury classified as grade 5.

CytomX disclosed that the patient had a "complex medical history," including having a solitary kidney. The company believes the kidney injury was secondary to nausea, vomiting, and diarrhea. The death was reported to CytomX on July 11, and the FDA was informed on July 18.

Company Response and Trial Continuation

Despite the tragic event, CytomX's CEO Sean McCarthy emphasized that patient safety remains their top priority. The study's safety review committee met on July 14 and advised that the trial should continue. McCarthy stated, "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."

CX-2051 targets EpCAM (Epithelial Cell Adhesion Molecule), described as a "previously undruggable" CRC antigen. The ADC incorporates a next-generation topoisomerase-1 inhibitor payload licensed from Immunogen.

Market Impact and Company Strategy

The news of the patient death has had a significant impact on CytomX's stock price, which dropped 23% to $1.77 in premarket trading on Thursday, down from $2.31 at the beginning of the week.

This development comes at a crucial time for CytomX, which recently repositioned CX-2051 as its top priority. Earlier this year, the company reassessed its plans for an Amgen-partnered EGFRxCD3-targeting T-cell engager and reduced its workforce by 40% to focus on ADCs. CytomX maintains collaborations with several major pharmaceutical companies, including Astellas, Bristol Myers Squibb, Moderna, and Regeneron.