Merck (NYSE: MRK) announced that it is discontinuing a cohort of the phase III study evaluating a co-formulation of its blockbuster PD-L1 inhibitor, Keytruda plus vibostolimab, its investigational anti-TIGIT antibody, as adjuvant treatment for patients with resected high-risk melanoma. Data from a pre-planned analysis of the study called KeyVibe-010 showed that the primary endpoint of recurrence-free survival (RFS) met the pre-specified futility criteria. A higher rate of patients discontinued all adjuvant therapy in the coformulation arm versus the Keytruda-only arm primarily due to immune-mediated adverse experiences. Due to this, it seemed unlikely that the study could achieve a statistically significant improvement in RFS. Accordingly, an independent Data Monitoring Committee (DMC) recommended unblinding the study and guided Merck to offer patients receiving the Keytruda+vibostolimab coformulation to be treated with Keytruda monotherapy. Merck continues to analyze data from the study and will share the data with the scientific community and regulatory agencies at a later date. At present, Keytruda is approved for two indications in melanoma. Phase III studies are ongoing evaluating Keytruda+vibostolimab coformulation in lung cancer. Merck's stock has risen 18.6% so far this year compared with an increase of 13.4% for the industry. Image Source: Zacks Investment Research This is the second Keytruda study to have failed in less than two weeks. Last week, a ...