Is surgery necessary for mismatch repair-deficient/microsatellite instability-high colorectal cancer patients with a clinical complete response after neoadjuvant immunotherapy? A retrospective cohort study with literature context.

BACKGROUND: The purpose of this study was to retrospectively compare the prognostic outcomes of patients with colorectal cancer (CRC) who achieved a clinical complete response (CCR) after neoadjuvant immunotherapy (NI) and those who achieved a CCR after surgery. A literature review of publications was conducted in the PubMed database. MATERIALS AND METHODS: This study included 70 patients who were diagnosed with mismatch repair deficiency/microsatellite instability high (dMMR/MSI-H) colorectal cancer and who were treated with NI between 2018 and 2024. CCR patients were grouped into the "watch and wait" (W&W) method group or the radical surgery group. Afterwards, the oncological and clinical outcomes of patients who achieved a clinical complete response (CCR) were compared to those of patients who were classified as tumour free. We also conducted a literature review of publications in the PubMed database of clinical studies that compared clinical outcomes between W&W and surgery for CCR dMMR/MSI-H patients. RESULTS: Among the 70 NI-treated dMMR/MSI-H CRC patients, 44 (62.86%) achieved a CCR. Of these, 25 patients were managed with a watch-and-wait (W&W) strategy, while 19 underwent curative-intent surgery. In the surgery group, 16 patients (84.21%) achieved a pathological complete response (pCR). During follow-up, 2 patients (10.53%) in the surgery group developed recurrence, and both subsequently died, while the remaining 17 patients were alive at the last follow-up. No statistically significant differences were observed between the W&W and surgery groups in terms of recurrence or survival outcomes. A literature review including nine studies further demonstrated comparable oncological outcomes between W&W and surgical management in patients who achieved a CCR. CONCLUSION: Patients in the W&W group presented similar oncological outcomes to those who underwent surgery. Surgery may not be necessary for patients with dMMR/MSI-H colorectal cancer who achieve a clinical complete response after neoadjuvant immunotherapy. However, large sample sizes and multicentre investigations are needed to validate these findings.