A Phase 3 Randomized Clinical Trial of Nivolumab Alone, Nivolumab in Combination With Ipilimumab, or Investigator's Choice Chemotherapy in Participants With Microsatellite Instability High (MSI-H) or Mismatch Repair Deficient (dMMR) Metastatic Colorectal Cancer

The main purpose of this study is to compare the clinical benefit, as measured by Progression-Free Survival (PFS), Objective Response Rate (ORR), and Overall Survival (OS), achieved by nivolumab in combination with ipilimumab or by nivolumab monotherapy in participants with Microsatellite Instability High (MSI-H) or Mismatch Repair Deficient (dMMR) metastatic colorectal cancer (mCRC). This study will also compare nivolumab plus ipilimumab combination vs chemotherapy for treatment of MSI-H/dMMR mCRC participants.