Survival outcomes in locally advanced dMMR rectal cancer: surgery plus adjunctive treatment vs. surgery alone.

Background: Recent studies have shown that deficient mismatch repair (dMMR) rectal cancer may be related to treatment resistance, resulting in a worse prognosis than proficient MMR (pMMR) rectal cancer. The purpose of this study was to explore whether surgery plus other treatments (radiotherapy and chemotherapy) can bring more benefits to these patients than surgery alone.

Methods: A retrospective study of 168 patients with rectal adenocarcinoma who underwent total mesorectal excision was conducted using immunohistochemical methods to determine MMR status and a propensity score matching model to minimize potential confounding factors between subgroups of patients with different treatment regimens. Kaplan-Meier analysis, log-rank tests, and Cox regression models were used to assess overall survival (OS) and disease-free survival (DFS) in patient subgroups.

Results: Only 6.9% (n = 168) of patients in the total cohort had dMMR rectal adenocarcinoma, and the most common cause of dMMR was a PMS2 deletion (103, 61.3%). The median DFS of the surgery alone group was 45.7 months (IQR, 40.9 to 77.8), and the median DFS of the surgery plus other treatment group was 43.9 months (IQR, 14.2 to 80.1). The surgery alone group was superior to the surgery plus other treatment group (HR, 0.16; 95% CI, 0.07 to 0.38; p = 0.005). There was no significant difference in OS (45.8 (IQR, 41.0 to 79.8) vs. 45.9 (IQR, 38.5 to 80.3)) between the two groups (HR, 0.57; 95% CI, 0.23 to 1.40; p = 0.263).

Conclusions: For patients with locally advanced dMMR rectal adenocarcinoma, compared with surgery alone, surgery plus other treatment options (radiotherapy and chemotherapy) do not grant long-term survival benefits but rather shorten DFS.