A study to evaluate the safety and efficacy of two dose levels of ONO-4578 with Opdivo®, in combination with mFOLFOX6 and bevacizumab versus standard of care in participants with non MSI-H/dMMR, PD-L1 positive advanced colorectal cancer.

Other illness

• Prior malignancy active within the previous 3 years except for locally curable cancers that have been apparently cured and considered to be of low risk of recurrence. Note: Other tumor types that are considered curable with local treatment may be eligible for enrollment after consultation with the sponsor. - Prior bone marrow or solid organ transplant.
• Gastrointestinal, Respiratory and Cardiovascular conditions as defined in the protocol.
• Gastrointestinal, Respiratory and Cardiovascular conditions as defined in the protocol. - History of medical conditions with treatments used in the study, as defined in the protocol. - Other medical conditions as defined in the protocol.

Other

• Participants with high microsatellite instability (MSI-High), or mismatch repair deficient (dMMR) tumor. - Participants with BRAF V600E mutation. - Active brain metastases or leptomeningeal metastases.
• Other exclusion criteria as defined in the protocol.

• Participant must be ≥18 years at the time of signing informed consent. - Able and willing to give informed consent. - Willing to participate and comply with the requirements of the entire trial.
• Histologically confirmed advanced (locally advanced or metastatic) colorectal cancer not amenable to curative resection. Note: Participants with left sided tumor and RAS wild-type who are not suitable for anti-EGFR therapy may be considered. - ECOG Performance Status of 0-1. - Available local test results for microsatellite stability or mismatch repair (MMR) status. - Available local test results for tumor BRAF mutation status. - No prior systemic treatment for advanced local or metastatic colorectal cancer (mCRC). - Presence of at least one measurable lesion as defined by RECIST v1.1 on diagnostic imaging assessed per local Investigator within 35 days prior to randomization.
• Adequate newly obtained or archival tumor tissue not previously irradiated is available for assessment of PD-L1 status by central laboratory. - Participants whose tumor is positive for PD-L1 expression (defined as Combined Positive Score (CPS) ≥ 1) as determined at a central laboratory.
• Participants with adequate bone marrow, renal, and hepatic function as defined in the protocol. Note: Hematology evaluations must be performed ≥ 7 days from last administration of blood, blood product transfusion and ≥ 14 days from hematologic growth factor products. Blood products and hematologic growth factors may not be administered within 14 days of C1D1.
• Female and male participants who agrees to use a highly effective contraceptive method as defined in the protocol.