PACE: A phase III trial of CAPOX versus anti-PD-1 inhibitor as adjuvant therapy for patients with dMMR/MSI-H stage III colon cancer.

TPS3637 Background: Approximately 12% of stage III colon cancer are deficient mismatch repair (dMMR), leading to high levels of microsatellite instability (MSI-H). In the KEYNOTE-177 study, the anti–PD-1 inhibitor Pembrolizumab alone significantly improved progression free survival (PFS) versus chemotherapy as first-line therapy for metastatic colorectal cancer (mCRC) patients with MSI-H/dMMR. We are conducting a phase III randomised trial to determine whether anti-PD-1 inhibitor Sintilimab monotherapy can improve disease free survival (DFS) compared with standard adjuvant chemotherapy in stage III colon cancer patients with dMMR. Methods: This is an open-label, multicentre, randomised phase III study. Patients aged ≥ 18 years with completely resected, stage III colon cancer confirmed to have dMMR/MSI-H and ECOG performance status 0-1 are eligible. Approximately 323 patients will be randomly assigned 1:1 to either Sintilimab monotherapy (200 mg IV every 3 weeks for 8 cycles) or CAPOX regimen (capecitabine, oxaliplatin for 4 or 8 cycles according to current standard practice). Adverse events (AEs) will be assessed throughout treatment and for 30 days thereafter (90 days for serious AEs) and graded per NCI CTCAE v4.0. Primary endpoint is 3-year DFS. The study was estimated to provide approximately 80% power to detect a hazard ratio of 0.56 for DFS at a two-sided alpha of 0.05. Secondary endpoints include OS, safety profile, toxicity, and quality of life. Archived tumor tissue and blood samples will be collected for correlative studies. Study enrollment is ongoing. Clinical trial information: NCT05236972 .