The main purpose of this study was to help meet the medical needs of people in China with certain types of solid tumors that have specific genetic changes called microsatellite instability-high (MSI-H) or deficient mismatch repair (dMMR). The study looked at how well the drug tislelizumab works and how safe it is when given before surgery (neoadjuvant treatment) for these types of tumors.

This study enrolled participants with Stage II or III resectable colorectal cancer (CRC). Participants with unknown microsatellite instability (MSI) or mismatch repair (MMR) status provided blood and tumor tissue samples during a prescreening period (within 56 days before the first dose) for central laboratory confirmation of MSI status. Participants with known MSI-high (MSI-H) or deficient MMR (dMMR) status by local laboratory also underwent central confirmation when tumor samples were available. Eligible participants received tislelizumab 200 mg by intravenous infusion once every 3 weeks for 3 cycles as neoadjuvant therapy. After completion of neoadjuvant treatment, participants underwent complete surgical removal (R0 resection) of their tumor, and surgical specimens were assessed for pathological response, including major pathological response (MPR) and pathological complete response (pCR). Post-surgery, participants continued adjuvant therapy and follow-up as determined by their investigator.

Inclusion Criteria:

• Participants had an Eastern Cooperative Oncology Group (ECOG) Performance Status score of 0 or 1.
• Participants had a pathologically (histologically) confirmed diagnosis of potentially resectable Stage II or Stage III colon or rectal cancer (CRC) with microsatellite instability-high (MSI-H) status confirmed by a sponsor-designated central laboratory, or known MSI-H status confirmed by a local laboratory. Participants were required to be eligible for complete surgical removal of the tumor (R0 resection) with curative intent.
• Participants had evaluable or measurable disease as assessed by the investigator according to the Response Evaluation Criteria in Solid Tumors (RECIST), version 1.1.
• Participants had adequate blood counts and organ function, as defined by protocol-specified laboratory test results obtained within 7 days before the first dose of study treatment.

Exclusion Criteria:

• Participants had received any prior treatment for their current colorectal cancer, including chemotherapy, radiotherapy, or immunotherapy.
• Participants had any condition requiring systemic treatment with corticosteroids at doses greater than 10 milligrams (mg) of prednisone per day, or other immunosuppressive medications within 14 days before the first dose.
• Participants had active autoimmune diseases or a history of autoimmune diseases that could potentially relapse.

Note: Additional protocol-defined inclusion and exclusion criteria may have applied.

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See plan description

See plan description

The Safety Analysis Set included all enrolled participants who received ≥ 1 dose of study drug

All-cause mortality is reported from enrollment through to the end of the study, maximum duration was 35 months. Adverse events are reported from the first dose until 30 days (or 90 days for imAEs) after the last dose of tislelizumab, death, or start of new anticancer therapy, whichever occurred first; Maximum treatment duration was 2.3 months.

All-cause mortality is reported for all randomized participants. Serious and other adverse events include all randomized participants who received ≥ 1 dose of any study treatment.