Microsatellite Instability-High (MSI-H)

This prospective, multicenter, single-arm phase II interventional study evaluates whether longitudinal circulating tumor DNA (ctDNA) monitoring can guide neoadjuvant immunotherapy and surgical decision-making in dMMR/MSI-H colon cancer. Participants with ctDNA clearance proceed to curative surgery, whereas those with persistent ctDNA positivity escalate to combined PD-1 and CTLA-4 inhibitor therapy.

Colorectal cancer of Mismatch Repair-deficient (dMMR)/ Microsatellite Instability-high (MSI-H) accounts for approximately 15% of all colorectal cancer patients, with a higher proportion in right colon cancer. Previous studies have found that colon cancer patients with dMMR/MSI-H cannot benefit from 5-fluorouracil (5-FU) adjuvant chemotherapy. Once patients have distant metastases, they are not sensitive to traditional palliative chemotherapy, and the prognosis is significantly worse than that of mismatch repair-proficient (pMMR)/microsatellite stability (MSS). A phase II clinical study of anti-PD-1 immunotherapy based on mismatch repair (MMR) status published in 《N Engl J Med》 showed that the objective response rate (ORR) of advanced colorectal cancer patients with dMMR received anti-PD-1 is 40%, and a longer response time can be obtained compared to conventional chemotherapy. Anti-PD-1 neoadjuvant therapy has proven to be safe and feasible in lung cancer, bladder cancer and malignant melanoma, and can achieve more than 40% of major pathological response. However, there are no reports of anti-PD-1 neoadjuvant therapy for the dMMR/MSI-H colorectal cancer. Therefore, the aim of this study was to find the best multidisciplinary treatment for resectable colorectal cancer patient with the dMMR/MSI-H phenotype and to explore whether cyclooxygenase (COX) inhibitors combined with anti-PD-1 monoclonal antibody (mAb) could further improve efficacy.