Stock reaction
Lyell Immunopharma Inc (NASDAQ:LYEL) saw its shares rise about 3% in premarket trading Monday following an announced amendment to its U.S. Phase 1 study of LYL273 in metastatic colorectal cancer. The company linked the share movement to safety improvements observed after introducing a gastrointestinal prophylaxis regimen.
Safety findings that prompted the amendment
Lyell reported that adding gastrointestinal prophylaxis in its U.S. Phase 1 trial reduced the incidence of Grade 2 or higher diarrhea or colitis from 55% without prophylaxis to 10% with prophylaxis. The prophylaxis approach used in the trial included infliximab, vedolizumab and budesonide together with a standardized safety management plan.
Trial amendment and new study structure
The ongoing Phase 1 trial has been amended and rebranded as CARABINER. The revised protocol now comprises four dose-escalation cohorts at Dose Levels 1 through 4 and introduces new cohorts such as a second-line cohort and a cohort assessing a combination strategy with radiotherapy. The amendment is intended to allow seamless expansion into a potential pivotal single-arm Phase 2 trial, contingent on regulatory alignment.
Enrollment and safety detail
As of May 5, 2026, nineteen patients had been enrolled in the U.S. Phase 1 trial across Dose Levels 1 and 2. Ten of those patients were treated under the new gastrointestinal prophylaxis regimen. According to the company, these ten patients did not experience Grade 3 or higher cytokine release syndrome or immune effector cell-associated neurotoxicity syndrome.
Efficacy signals and regulatory status
Lyell previously reported a 50% overall response rate across Dose Levels 1 and 2 in patients with third- or later-line relapsed or refractory metastatic colorectal cancer. The U.S. Food and Drug Administration has granted LYL273 Fast Track designation for the treatment of metastatic colorectal cancer.
Outlook and next milestones
The company expects to report additional Phase 1 clinical data, including clinical outcomes, and to hold an End-of-Phase 1 meeting with the FDA in the second half of 2026. Dose escalation is ongoing and the maximum tolerated dose has not yet been determined.
Note: The amendment anticipates enrollment of up to sixty patients across the new cohorts as the CARABINER study proceeds.