Microsatellite Instability-High

The PICC-3 study is a multicentre, single-arm, phase II trial evaluating toripalimab plus celecoxib in patients with mismatch repair-deficient (dMMR) or microsatellite instability-high (MSI-H) locally advanced colorectal cancer. The trial uses a response-adapted treatment strategy, whereby patients with clinical complete response (cCR) after therapy may enter a non-operative management pathway, while patients without cCR proceed to surgery. Response assessment is based on imaging, endoscopy, biopsy evaluation, and ctDNA analysis.

This open-label phase III trial investigates the efficacy of two cycles of PD-1 blockade (Tislelizumab) as adjuvant therapy to see how it works compared with standard of care (SOC) in treating patients with stage II dMMR/MSI-H colorectal cancer. The rational of giving PD-1 blockade as adjuvant therapy is based on the fact that tumor recurrence is extremely low among patients receiving neoadjuvant immunotherapy, which suggests that PD-1 blockade may likely improve patients' long-term survival. As for the short course (two cycles), we have the following considerations: firstly, the NICHE-2 trial, which adopted a two-cycle regimen, reported no recurrences during follow-up, suggesting that short-course anti-PD-1 therapy may be sufficient to improve the survival of patients with localized dMMR/MSI-H colorectal cancer. Secondly, the potential benefits of PD-1 blockade should be balanced against its toxicities, because patients with stage-II dMMR colorectal cancer generally have a good prognosis. Two cycles of PD-1 blockade have been shown to have a good safety profile, with low incidence of grade 3-4 and immune-related adverse events.