Merck Halts Development of Vibostolimab and Favezelimab Following Trial Setbacks

Merck Research Laboratories has announced an end to the clinical development of two immunotherapy candidates following disappointing results in Phase 3 studies. The decision marks a significant shift in the company’s oncology pipeline strategy.

Vibostolimab Program Discontinued Over Efficacy Concerns

The company has decided to terminate the vibostolimab development program, which combines the anti-TIGIT antibody with pembrolizumab. This fixed-dose combination was being tested in the KeyVibe series of trials targeting non-small cell lung cancer patients.

The halting of this program stems from efficacy outcomes in two pivotal studies. An independent Data Monitoring Committee recommended discontinuing the Phase 3 KeyVibe-003 and KeyVibe-007 trials after both studies failed to meet pre-specified efficacy benchmarks for overall survival. These trials were assessing the combination therapy against the primary endpoint of overall survival in certain patient populations with non-small cell lung cancer.

Notably, the safety profile of the vibostolimab and pembrolizumab combination remained consistent with previous observations. Immune-related adverse events were observed at higher rates compared to pembrolizumab alone, which is typical when using dual checkpoint inhibitor approaches. No unexpected safety signals emerged from the data review.

Beyond KeyVibe-007 and KeyVibe-003, Merck is also closing the Phase 3 KeyVibe-006 trial and halting other vibostolimab studies as a result of the cumulative efficacy data across the entire KeyVibe clinical development program.

Favezelimab Clinical Program Ends

In a parallel move, Merck has elected to terminate favezelimab development entirely. The anti-LAG-3 antibody was being evaluated with pembrolizumab as part of the KEYFORM clinical program for treating relapsed or refractory classical Hodgkin lymphoma patients whose disease progressed after prior anti-PD-1 therapy.

The company will cease new patient enrollment in the Phase 3 KEYFORM-008 trial, though those already enrolled may continue on therapy through study completion. KEYFORM-008 represents the only Phase 3 study within the KEYFORM program without available results.

The company emphasized that this discontinuation decision does not reflect safety concerns with the favezelimab and pembrolizumab combination, but rather reflects a strategic prioritization of other oncology candidates within Merck’s broader development portfolio.

What’s Next

Merck is communicating directly with trial investigators and encouraging patients in these studies to consult with their study teams and healthcare providers about alternative treatment options. Data analyses for the terminated Phase 3 trials are continuing, and findings will be shared with the scientific community.

Dr. Marjorie Green, senior vice president and head of oncology global clinical development at Merck Research Laboratories, stated: “Following careful analysis of the data, we determined that ending development of these candidates allows us to concentrate resources on other promising programs. We remain grateful to patients, caregivers, and investigators who participated in these studies.”

The decision reflects Merck’s commitment to advancing the most promising scientific approaches in its comprehensive oncology pipeline, with focus on agents demonstrating the greatest potential for improving patient outcomes.