A patient has died from kidney injury in a trial of CytomX Therapeutics’ lead antibody-drug conjugate, although the biotech has been advised to stick with the study.
CytomX has so far enrolled 73 patients in a phase 1 study of the ADC, dubbed CX-2051, in metastatic colorectal cancer. CX-2051 is aimed at a “previously undruggable” CRC antigen called EpCAM (Epithelial Cell Adhesion Molecule) and includes the payload of a next-gen topoisomerase-1 inhibitor licensed from Immunogen.
About 20 patients have entered a dose expansion portion of the study, where they receive either 7.2-mg/kg, 8.6-mg/kg or 10-mg/kg doses of CX-2051 every three weeks. It was one of these patients who experienced a treatment-related acute kidney injury described as grade 5—meaning it resulted in a fatality.
The grade 5 event was “believed to be secondary to nausea, vomiting and diarrhea,” CytomX explained in an Aug. 13 release. The individual in question had a “complex medical history,” the biotech pointed out, including “having a solitary kidney.”
CytomX was made aware of the death July 11 and informed the FDA July 18. Meanwhile, the study’s safety review committee met July 14 and advised that the trial should be continued.
“Since our initial data disclosure in May 2025, phase 1 enrollment has been rapid and is substantially complete,” CytomX CEO Sean McCarthy said in a statement. “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,” McCarthy added.
Having opened the week at $2.31, CytomX’s stock has since dropped 23% to sit at $1.77 in premarket trading Thursday.
CytomX moved CX-2051 to the top of its priority list at the start of the year, when the company reassessed its plans for a Amgen-partnered EGFRxCD3-targeting T-cell engager. The biotech’s focus on ADCs came with a 40% reduction in the company's workforce.
As well as Amgen, CytomX has an array of ongoing collaborations with the likes of Astellas, Bristol Myers Squibb, Moderna and Regeneron. The biotech also has another wholly owned candidate in the clinic in the form of CX-801, a masked interferon alpha-2b cytokine being tested for solid tumors.