The death was linked to acute kidney injury in a patient who had a single kidney remaining and a “complex medical history,” according to CytomX.
A patient has died in CytomX’s Phase I trial for CX-2051, an investigational antibody-drug conjugate being tested for colorectal cancer.
The California biotech made the disclosure Wednesday morning, noting that the mortality was linked to acute kidney injury in a patient with a “complex medical history.” CytomX noted that the patient in question had only one kidney. The company found out about the death on July 11 and reported the event to the FDA on July 18, “in accordance with regulatory requirements,” according to the news release.
The safety review board for the Phase I study convened days after the death and endorsed the continuation of the trial. Data are expected in the first quarter of 2026.
CytomX shares dipped as much as 14% to $1.78 at close of trading Wednesday.
Designed to target the epithelial cell adhesion molecule (EpCAM), CX-2051 is a conditionally activated antibody-drug conjugate (ADC) that according to CytomX’s website has “potential applicability” across cancers expressing the EpCAM marker. The biotech is currently running an early-stage program for CX-2051 in solid tumors, with a focus on advanced colorectal cancer.
CytomX released interim data for CX-2051 in May, noting that in 18 evaluated patients, five achieved confirmed partial response, resulting in a 28% overall response rate. At the highest dose level of 10 mg/kg, 43% of treated patients hit confirmed partial response. Disease control rate was 94% across all dose arms.
At the time, CytomX said that CX-2051 was “generally well-tolerated with manageable adverse events” and had no dose-limiting toxicities. However, the company also reported five cases of grade 3 diarrhea and one of nausea.
Beyond the readout expected in early 2026, CytomX is also planning a Phase II initiation for CX-2051 in advanced late-line colorectal cancer in the first half of 2026, according to a company announcement in May. The biotech is also looking to potentially start combination studies for the ADC in earlier lines of colorectal cancer, as well as a Phase Ib study to assess its potential in other solid tumors.
As of June 30, CytomX still had $158.1 million in cash, cash equivalents and investments, which it expect will be enough to keep afloat into the second quarter of 2027. In January, the biotech shaved its headcount by 40%, laying off around 48 employees, to focus resources on the development of CX-2051.
