Merck Ends Phase III Anti-TIGIT, Keytruda Skin Cancer Study with High Dropouts

Merck Canada Office/iStock, JHVE Photo

Pictured: Merck office building in Canada/iStock, JHVEPhoto

Following a high rate of adverse experience-related dropouts, Merck called it quits Monday on a Phase III trial of its anti-TIGIT antibody vibostolimab and anti-PD-1 therapy Keytruda in skin cancer. 

The late-stage study was evaluating vibostolimab as an adjuvant treatment to Keytruda in patients with resected, high-risk melanoma. The investigational anti-TIGIT antibody works by restoring antitumor activity by blocking the TIGIT receptor from binding to its ligands to help T lymphocytes destroy tumor cells.  

A pre-planned analysis revealed the high rate of dropouts, primarily due to immune-mediated adverse events, making it “highly unlikely that the trial could achieve a statistically significant improvement” in recurrence-free survival.

Based on the recommendation of an independent data monitoring committee, Merck said it is unblinding the study to offer Keytruda alone to patients who had been receiving the combination treatment and sharing the results with the scientific community and regulatory agencies. 

Keytruda is currently approved in two skin cancer indications for patients with metastatic or unresectable melanoma, and as an adjuvant for certain stages following surgery. Merck continues efforts to move its blockbuster anti-PD-1 therapy up to an earlier line of treatment. The company is pursuing an ongoing Phase III study combining Keytruda with Moderna’s individualized neoantigen therapy, V940, in patients with resected, high-risk melanoma. 

“We continue to ask the tough questions in an effort to fully explore the potential of novel coformulations and combinations that build on the foundation of Keytruda, with a goal to improve upon current standards of care and help even more patients with cancer,” Marjorie Green, head of oncology for Merck Research Laboratories, said in a statement. 

The Keytruda-vibostolimab coformulation is in ongoing Phase III trials for lung cancer. Merck pointed out in Monday’s announcement that interim safety reviews have not resulted in any study modifications in these studies.  

In December 2023, the company announced the combination treatment failed to meet endpoints in a Phase II study of metastatic non-small cell lung cancer patients with progressive disease after treatment with immunotherapy and chemotherapy.  

Kate Goodwin is a freelance life science writer based in Des Moines, Iowa. She can be reached at and on LinkedIn

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