[Organ preservation in locally advanced colorectal cancer with microsatellite instability-high after immunotherapy]

Neoadjuvant immunotherapy has achieved exciting efficacy with high clinical complete response (cCR) and pathologic complete response (pCR) rates and durable long-term effects. PD-1 checkpoint blockade-based immunotherapy has been highly successful in microsatellite instability high (MSI-H)/mismatch repair deficiency (dMMR) colorectal cancer and has been recommended as the first-line treatment for metastatic colorectal cancer by domestic and international guidelines. Several studies have shown that immunotherapy can be a potentially curable treatment for MSI-H rectal cancer and has even shown promise in organ preservation in colon cancer. In this study, we first clarified the feasibility of the watch-and-wait strategy after PD-1 checkpoint blockade treatment by indirect and direct evidence. Then from the assessment tools (including digital rectal examination, endoscopy, radiology, and lymph node assessment), the viable assessment methods of cCR for immunotherapy and related difficulties are proposed. Finally, the medication choices of immunotherapy, the treatment regimen, and the follow-up strategy are further discussed. We hope that neoadjuvant immunotherapy could be appropriately applied in MSI-H/dMMR colorectal cancer so that more patients can achieve organ preservation.