A Study of Efficacy and Safety of Pembrolizumab Plus Enfortumab Vedotin (EV) +/- Investigational Agents in First-Line Metastatic Urothelial Carcinoma (mUC) (MK-3475-04B/KEYMAKER-U04)

This study is a substudy being conducted under one pembrolizumab umbrella master study KEYMAKER-U04. The substudy will consist of 2 parts. Part 1 will evaluate the efficacy and safety of coformulated favezelimab/pembrolizumab plus EV and coformulated vibostolimab/pembrolizumab plus EV relative to pembrolizumab plus EV. There will be no comparison of coformulated favezelimab/pembrolizumab plus EV versus coformulated vibostolimab/pembrolizumab plus EV. If ORR and/or DRR are substantially better on coformulated favezelimab/pembrolizumab plus EV and/or coformulated vibostolimab/pembrolizumab plus EV compared with pembrolizumab plus EV, after evaluation of the totality of data, the sponsor might consider Part 2 (expansion) to further characterize the efficacy and safety of the treatment arms under study.