Study of Pembrolizumab (MK-3475) Versus Chemotherapy in Chinese Participants With Stage IV Colorectal Cancer (MK-3475-C66)

The main inclusion and exclusion criteria include but are not limited to the following:

Inclusion Criteria:

Inclusion Criteria include, but are not limited to:

• Has a histologically confirmed diagnosis of colorectal adenocarcinoma that is atstage IV (as defined by American Joint Committee on Cancer eighth edition) [NationalComprehensive Cancer Network 2018]

• Has centrally confirmed Microsatellite Instability-High/Mismatch Repair Deficient (MSI-H/dMMR) status

• Has centrally confirmed RAS and BRAF mutation status

• A woman of child-bearing potential (WOCBP) must have a negative highly sensitivepregnancy test (urine or serum as required by local regulations) within 24 hours forurine or within 72 hours for serum before the first dose of study intervention.

• Has measurable disease per Response Evaluation Criteria In Solid Tumors (RECIST) 1.1as assessed by the local site investigator/radiology

• Must provide an archival tumor tissue sample or newly obtained core or excisionalbiopsy of a tumor lesion not previously irradiated.

• Has an Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 1 within 3 days before randomization

• Has a life expectancy of at least 3 months

• Has received Hepatitis B Virus (HBV) antiviral therapy for at least 4 weeks, andhave undetectable hepatitis B virus (HBV) viral load prior to randomization ifhepatitis B surface antigen (HBsAg) positive

• Has an undetectable Hepatitis C Virus (HCV) viral load if HCV infected

• Has well controlled Human Immunodeficiency Virus (HIV) on antiretroviral therapy (ART) if HIV infected

Exclusion Criteria:

Exclusion Criteria include, but are not limited to:

• Has received prior systemic therapy for stage IV colorectal cancer (CRC).Participants may have received prior adjuvant/neoadjuvant chemotherapy for CRC aslong as it was completed at least 6 months prior to randomization

• Has undergone major operation within 4 weeks of randomization or has not adequatelyrecovered from major surgery or has ongoing surgical complications

• Has received prior therapy with an anti-programmed cell death 1 protein (anti-PD-1),anti-programmed cell death ligand 1 (anti-PD-L1), or anti-programmed cell deathligand 2 (anti PD-L2) agent or with an agent directed to another stimulatory orcoinhibitory T-cell receptor (eg, cytotoxic T-lymphocyte-associated protein 4 [CTLA-4], tumor necrosis factor receptor superfamily, member 4 [OX 40], tumornecrosis factor receptor superfamily member 9 [CD137])

• Has received prior radiotherapy within 2 weeks of start of study intervention or hasradiation-related toxicities, requiring corticosteroids

• Has received a live or live-attenuated vaccine within 30 days before the first doseof study intervention

• Has received an investigational agent or has used an investigational device within 4weeks prior to study intervention administration.

• Has a diagnosis of immunodeficiency or is receiving chronic systemic steroid therapy (in dosing exceeding 10 mg daily of prednisone equivalent) or any other form ofimmunosuppressive therapy within 7 days prior to the first dose of study medication

• Has a known additional malignancy that is progressing or has required activetreatment within the past 5 years, with the exception of basal cell carcinoma of theskin, squamous cell carcinoma of the skin, or carcinoma in situ (eg, breastcarcinoma, cervical cancer in situ) that have undergone potentially curative therapyare not excluded

• Has known active central nervous system (CNS) metastases and/or carcinomatousmeningitis

• Has severe hypersensitivity (≥Grade 3) to pembrolizumab and/or any of its excipients

• Has an active autoimmune disease that has required systemic treatment in past 2years

• Has a history of (noninfectious) pneumonitis/interstitial lung disease that requiredsteroids or has current pneumonitis/interstitial lung disease

• Has an active infection requiring systemic therapy (eg, tuberculosis, known viral orbacterial infection)

• Has HIV-infection with a history of Kaposi's sarcoma or Multicentric Castleman'sDisease

• Has had an allogenic tissue/solid organ transplant