Neoadjuvant Immunotherapy Alone for Patients With Locally Advanced and Resectable Metastatic Colorectal Cancer of dMMR/MSI-H Status.

BACKGROUND The use of programmed death-1 blockade has a significant therapeutic effect in patients with Mismatch Repair-Deficient/Microsatellite Instability-High metastatic colorectal cancer. However, data on preoperative single-agent programmed death-1 blockade are rare. OBJECTIVE This study aims to evaluate the effectiveness and safety of preoperative programmed death-1 blockade as a conversion strategy in patients with locally advanced and resectable metastatic Mismatch Repair-Deficient/Microsatellite Instability-High colorectal cancer. DESIGN This is a retrospective observational study. SETTINGS This study was conducted at a high-volume tertiary referral cancer center in China. PATIENTS Twenty-four patients of consecutive cases since 2020-2022 with Mismatch Repair-Deficient/Microsatellite Instability-High colorectal cancer who received preoperative single-agent programmed death-1 blockade were retrospectively reviewed. These patients had either bulking tumor scheduled for multivisceral resection, a strong desire for organ preservation, or potentially resectable metastatic lesions. MAIN OUTCOME MEASURES Pathological complete response, clinical complete response, toxicity, R0 resection rate, and complications were evaluated. RESULTS Patients tolerated preoperative immunotherapy well. The R0 resection rate was 95.2% and the pathological complete response rate was 47.6%. Three patients (12.5%) were evaluated as clinical complete response and then underwent "watch and wait". One half of the cT4b patients were spared multivisceral resection, while 60% (3/5) achieved pathological complete response. All three patients with liver metastases obtained CR of all liver lesions after programmed death-1 blockade treatment. Grade III postoperative complications occurred in two patients. LIMITATIONS The limitations of this study are as follows: retrospective study, small sample size, and short follow-up. CONCLUSIONS Preoperative anti-programmed death-1 therapy alone as a conversion strategy in initially resected difficult dMMR/MSI-H colorectal cancer can achieve a high tumor complete response. The use of immuno-preoperative therapy in patients with T4b colon cancer or low rectal cancer can reduce multivisceral resection and achieve high organ function preservation. See Video Abstract.