A Study of Nivolumab, Nivolumab Plus Ipilimumab, or Investigator's Choice Chemotherapy for the Treatment of Participants With Deficient Mismatch Repair (dMMR)/Microsatellite Instability High (MSI-H) Metastatic Colorectal Cancer (mCRC)

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.

Inclusion Criteria: * Histologically confirmed recurrent or metastatic colorectal cancer (CRC) irrespective of prior treatment history with chemotherapy and/or targeted agents not amenable to surgery (Applicable only during Part 1 enrollment of the study) * Histologically confirmed recurrent or metastatic CRC with no prior treatment history with chemotherapy and/or targeted agents for metastatic disease and not amenable to surgery (Applicable during Part 2 enrollment of the study) * Known tumor microsatellite instability-high (MSI-H) or mismatch repair deficient (dMMR) status per local standard of practice * Eastern cooperative oncology group (ECOG) performance status lower than or equal to 1 Exclusion Criteria: * An active, known or suspected autoimmune disease * History of interstitial lung disease or pneumonitis * Known history of positive test for human immunodeficiency virus (HIV) or known acquired immunodeficiency syndrome (AIDS) Other protocol-defined inclusion/exclusion criteria apply