Despite a patient death occurring in its Phase I trial on investigative antibody-drug conjugate (ADC) CX-2051, CytomX Therapeutics will continue with the study.
The patient, who had one kidney when the trial commenced, experienced a treatment-associated Grade 5 event linked to acute kidney injury. However, CytomX suggested that the death was secondary to vomiting, diarrhoea and nausea. The company also noted that the patient in question had a “complex medical history” in a 13 August statement.
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By GlobalDataThis patient was assigned to the CX-2051 dose expansion group, with patients in this arm allocated to receive 7.2mg/kg, 8.6mg/kg and 10mg/kg doses, every three weeks.
The company was informed of this death on 11 July 2025, which led it to report the event to the US Food and Drug Administration (FDA) on 18 July in line with current regulations.
Following a positive safety committee meeting, CytomX has chosen to continue the trial, which has enrolled 73 patients with colorectal cancer. The company plans to provide a Phase I data update in Q1 2026.
CytomX CEO and chair Dr Sean McCarthy said: “Since our initial data disclosure in May 2025, Phase I enrolment has been rapid and is substantially complete.
“Patient safety remains our top priority as we continue to advance CX-2051 for the treatment of CRC.”
This negative publicity will not be welcome for CytomX, which had already had a securities class action lawsuit filed in 2020.
During this legal debate, the plaintiff alleged that the company misled investors regarding the efficacy of its investigational cancer therapies, CX-2009 and CX-072. It also raised concerns about alleged safety issues associated with CX-2009.
Though the lawsuit was later dismissed by the US District Court for the Northern District of California, the company’s stock fell by 36% following this news.
CytomX’s stock has progressively devalued since this point, with the company experiencing a 74% drop on the Nasdaq exchange market since 2021.
The Phase I development also triggered a further stock drop for CytomX, with the company’s value decreasing by 21%, from $2.27 at market open on 12 August to $1.79 at close on 13 August following the news.
The company, which is currently progressing its trio of investigational ADCs through the clinical pipeline, established partnerships with key pharma names such as Amgen, Astellas, Bristol Myers Squibb (BMS), Moderna and Regeneron.
However, Amgen and CytomX decided to discontinue further development of their previous project, CX-904, based on clinical observations in January 2025. This is a similar story to the company’s partnership with BMS, which was axed after the big pharma tightened its portfolio in 2024.
Both these companies, however, are still working with CytomX on preclinical projects.
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