CytomX Reports Patient Death in ADC Trial, Continues Study Despite Setback

CytomX Therapeutics has reported a patient death due to kidney injury in a phase 1 trial of its lead antibody-drug conjugate (ADC), CX-2051, for metastatic colorectal cancer. Despite this setback, the company has been advised to continue the study, highlighting the complex balance between potential therapeutic benefits and patient safety in oncology trials.

Trial Details and Patient Outcome

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 fatal incident occurred in a patient with a complex medical history, including a solitary kidney, who experienced a treatment-related acute kidney injury described as grade 5.

CytomX CEO Sean McCarthy stated, "Patient safety remains our top priority as we continue to advance CX-2051 for the treatment of CRC." The company was made aware of the death on July 11 and promptly informed the FDA on July 18. Despite this event, the study's safety review committee, which met on July 14, advised that the trial should continue.

CX-2051: Targeting the "Undruggable" EpCAM

CX-2051 is designed to target EpCAM (Epithelial Cell Adhesion Molecule), described as a "previously undruggable" colorectal cancer antigen. The ADC incorporates a next-generation topoisomerase-1 inhibitor payload licensed from Immunogen, showcasing the collaborative nature of drug development in the oncology space.

McCarthy remains optimistic about the trial's progress, stating, "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."

Market Response 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 reaction underscores the high-stakes nature of clinical trials in the biopharmaceutical industry.

CytomX's focus on ADCs comes after a strategic reassessment earlier this year, which included a 40% reduction in the company's workforce. The company has positioned CX-2051 at the top of its priority list, while also maintaining collaborations with industry giants such as Amgen, Astellas, Bristol Myers Squibb, Moderna, and Regeneron.

In addition to CX-2051, CytomX is advancing another wholly-owned candidate, CX-801, a masked interferon alpha-2b cytokine being tested for solid tumors. This diversified pipeline strategy demonstrates the company's commitment to developing innovative cancer therapies despite the challenges inherent in clinical development.