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)

Progression-free Survival (PFS) by Blinded Independent Review Center (BICR) - 1L Participants

BICR-assessed Progression-free survival (PFS) is defined as the time from the randomization date to the date of first objectively documented disease progression per RECIST 1.1 (i.e, radiologic) or death due to any cause, whichever occurs first.

Time frame: From date of randomization to the date of first objectively documented disease progression or death due to any cause, whichever occurs first

Progression-free Survival (PFS) by Blinded Independent Review Center (BICR) - Arm B vs. Arm A All Randomized Participants

BICR-assessed Progression-free survival (PFS) is defined as the time from the randomization date to the date of first objectively documented disease progression per RECIST 1.1 (i.e, radiologic) or death due to any cause, whichever occurs first.

Time frame: From date of randomization to the date of first objectively documented disease progression or death due to any cause, whichever occurs first (Up to approximately 60 months)

Progression-free Survival (PFS) by Blinded Independent Review Center (BICR) - 1L Randomized Participants

BICR-assessed Progression-free survival (PFS) is defined as the time from the randomization date to the date of first objectively documented disease progression per RECIST 1.1 (i.e, radiologic) or death due to any cause, whichever occurs first.

Time frame: From date of randomization to the date of first objectively documented disease progression or death due to any cause, whichever occurs first (Up to approximately 60 months)

Progression-free Survival (PFS) by Blinded Independent Review Center (BICR) - Crossover and First Line Arm

BICR-assessed Progression-free survival (PFS) is defined as the time from the randomization date to the date of first objectively documented disease progression per RECIST 1.1 (i.e, radiologic) or death due to any cause, whichever occurs first.

Time frame: From date of randomization to the date of first objectively documented disease progression or death due to any cause, whichever occurs first

Progression-free Survival (PFS) by Blinded Independent Review Center (BICR) by Polymerase Chain Reaction (PCR) - Arm B vs. Arm A

BICR-assessed Progression-free survival (PFS) is defined as the time from the randomization date to the date of first objectively documented disease progression per RECIST 1.1 (i.e, radiologic) or death due to any cause, whichever occurs first.

Time frame: From date of randomization to the date of first objectively documented disease progression or death due to any cause, whichever occurs first (Up to approximately 60 months)

Progression-free Survival (PFS) by Blinded Independent Review Center (BICR) by Immunohistochemistry (IHC) - Arm B vs. Arm A

BICR-assessed Progression-free survival (PFS) is defined as the time from the randomization date to the date of first objectively documented disease progression per RECIST 1.1 (i.e, radiologic) or death due to any cause, whichever occurs first.

Time frame: From date of randomization to the date of first objectively documented disease progression or death due to any cause, whichever occurs first (Up to approximately 60 months)

Progression-free Survival (PFS) by Blinded Independent Review Center (BICR) by Polymerase Chain Reaction (PCR) - Arm B vs. Arm C

BICR-assessed Progression-free survival (PFS) is defined as the time from the randomization date to the date of first objectively documented disease progression per RECIST 1.1 (i.e, radiologic) or death due to any cause, whichever occurs first.

Time frame: From date of randomization to the date of first objectively documented disease progression or death due to any cause, whichever occurs first (Up to approximately 32 months)

Progression-free Survival (PFS) by Blinded Independent Review Center (BICR) by Immunohistochemistry (IHC) - Arm B vs. Arm C

BICR-assessed Progression-free survival (PFS) is defined as the time from the randomization date to the date of first objectively documented disease progression per RECIST 1.1 (i.e, radiologic) or death due to any cause, whichever occurs first.

Time frame: From date of randomization to the date of first objectively documented disease progression or death due to any cause, whichever occurs first (Up to approximately 32 months)

Progression-free Survival (PFS) by Investigator- Arm B vs. Arm A All Lines

Investigator-assessed Progression-free survival (PFS) is defined as the time from the randomization date to the date of first objectively documented disease progression per RECIST 1.1 (i.e, radiologic) or death due to any cause, whichever occurs first.

Time frame: From date of randomization to the date of first objectively documented disease progression or death due to any cause, whichever occurs first (Up to approximately 60 months)

Progression-free Survival (PFS) by Investigator - Arm A and Arm B All Lines With dMMR/MSI-H mCRC

Investigator-assessed Progression-free survival (PFS) is defined as the time from the randomization date to the date of first objectively documented disease progression per RECIST 1.1 (i.e, radiologic) or death due to any cause, whichever occurs first.

Time frame: From date of randomization to the date of first objectively documented disease progression or death due to any cause, whichever occurs first (Up to approximately 60 months)

Progression-free Survival (PFS) by Investigator - 1L Participants

Investigator-assessed Progression-free survival (PFS) is defined as the time from the randomization date to the date of first objectively documented disease progression per RECIST 1.1 (i.e, radiologic) or death due to any cause, whichever occurs first.

Time frame: From date of randomization to the date of first objectively documented disease progression or death due to any cause, whichever occurs first (Up to approximately 60 months for arm A and arm B; up to 32 months for arm C)

Objective Response Rate (ORR) by Blinded Independent Review Center (BICR) - Arm A and Arm B All Lines With dMMR/MSI-H mCRC

Objective Response Rate (ORR) is defined as the percentage of all randomized participants whose best overall response is either confirmed complete response (CR) or confirmed partial response (PR). CR= Disappearance of all target lesions. Any pathological lymph nodes (whether target or non-target) must have reduction in short axis to \< 10 mm. PR= At least a 30% decrease in the sum of diameters of target lesions, taking as reference the baseline sum diameters. Progressive disease (PD)=At least a 20% increase in the sum of diameters of target lesions. the sum must also demonstrate an absolute increase of at least 5 mm.

Time frame: From date of randomization to the date of the initial objectively documented tumor progression, or the date of initiation of subsequent therapy, whichever occurs first (Up to approximately 60 months)

Objective Response Rate (ORR) by Blinded Independent Review Center (BICR) - 1L Participants

Objective Response Rate (ORR) is defined as the percentage of all randomized participants whose best overall response is either confirmed complete response (CR) or confirmed partial response (PR). CR= Disappearance of all target lesions. Any pathological lymph nodes (whether target or non-target) must have reduction in short axis to \< 10 mm. PR= At least a 30% decrease in the sum of diameters of target lesions, taking as reference the baseline sum diameters. Progressive disease (PD)=At least a 20% increase in the sum of diameters of target lesions. the sum must also demonstrate an absolute increase of at least 5 mm.

Time frame: From date of randomization to the date of the initial objectively documented tumor progression, or the date of initiation of subsequent therapy, whichever occurs first (Up to approximately 60 months)

Overall Survival (OS) - Arm B vs. Arm A All Lines With dMMR/MSI-H mCRC

Overall Survival (OS) is defined as the time from the randomization date to the date of death due to any cause. A participant who has not died will be censored at last known date alive.

Time frame: From randomization to the date of death due to any cause (Up to approximately 60 months)

Overall Survival (OS) - 1L Participants

Overall Survival (OS) is defined as the time from the randomization date to the date of death due to any cause. A participant who has not died will be censored at last known date alive.

Time frame: From randomization to the date of death due to any cause