Merck Halts Phase III Anti-TIGIT, Keytruda Skin Cancer Study Due to High Dropouts

Merck has decided to halt a Phase III trial of its anti-TIGIT antibody vibostolimab combined with its anti-PD-1 therapy Keytruda in treating skin cancer due to a high dropout rate caused by adverse experiences. The trial was intended to evaluate the efficacy of vibostolimab as an adjunct to Keytruda for patients with resected, high-risk melanoma. Vibostolimab functions by inhibiting the TIGIT receptor, which theoretically allows T lymphocytes to attack and destroy tumor cells more effectively.

However, a pre-planned analysis indicated that the trial was facing a significant number of dropouts, primarily due to immune-mediated adverse events. This high dropout rate made it improbable that the study would achieve a statistically significant improvement in recurrence-free survival. Consequently, an independent data monitoring committee recommended that Merck discontinue the trial. Following this recommendation, Merck decided to unblind the study to allow patients who were on the combination therapy to switch to Keytruda alone. The company also plans to share the trial results with the scientific community and regulatory bodies.

Keytruda is already approved for use in two skin cancer indications: for patients with metastatic or unresectable melanoma and as an adjuvant treatment following surgery for certain stages of the disease. Merck is continuing its efforts to bring Keytruda into earlier lines of treatment. One such effort is an ongoing Phase III study that combines Keytruda with Moderna’s individualized neoantigen therapy, V940, for patients with resected, high-risk melanoma.

Marjorie Green, who leads the oncology division at Merck Research Laboratories, emphasized the company’s commitment to exploring novel combinations and coformulations that could potentially improve the current standards of care. She highlighted that the focus remains on helping more cancer patients by building on the foundation established by Keytruda.

Despite the setback in the skin cancer trial, the Keytruda-vibostolimab combination is still being investigated in ongoing Phase III trials for lung cancer. Merck noted that interim safety reviews for these lung cancer studies have not led to any changes, indicating a more favorable safety profile in this context.

Previously, in December 2023, Merck announced that the combination of Keytruda and vibostolimab did not meet its endpoints in a Phase II trial involving patients with metastatic non-small cell lung cancer, who had progressive disease following prior treatments with immunotherapy and chemotherapy.

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