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