The benefit of adjuvant chemotherapy in pathological T1-3N0M0 rectal mucinous adenocarcinoma: no improvement survival outcomes based on long-term survival analysis of large population data.

Background: Currently, the benefits of the administration of adjuvant chemotherapy (AT) in pathological low-risk rectal mucinous adenocarcinoma (RM) with T1-3N0M0 are unclear. The objective of this study is to retrospectively investigate the clinical significance of AT in terms of survival outcomes for patients with pathological T1-3N0M0 RM using data from a large population. Methods: The patient data were collected from the Surveillance, Epidemiology, and End Results (SEER) Program. The Chi-squared test was used to analyze categorical variables. The survival curves were compared using the log-rank test and the Kaplan-Meier method. A multivariate proportional hazards regression (Cox) model was applied to identify the independent prognostic factors of survival outcomes. Propensity score matching (PSM) was utilized to eliminate the differences between groups and estimate AT's effect. Results: The median follow-up duration for the rectal cancer (RC) cohort was 116 months. Multivariate analyses revealed that RM was a significant adverse prognostic factor, correlating with poorer overall survival (OS) and cancer-specific survival (CSS) for RC [hazard ratio (HR): 1.226, 95% confidence interval (CI): 1.094-1.375, P<0.001; HR: 1.446, 95% CI: 1.242-1.683, P<0.001]. Among patients with RM, the rates of 5-year OS and CSS were 68.6% and 79.3% in the AT (-) group, respectively. Additionally, the AT (+) group exhibited similar rates of 65.6% for 5-year OS and 74% for CSS (P=0.80, P=0.26). Subtype analysis according to preoperative therapy status showed that AT also did not significantly affect survival outcomes (P=0.65, P=0.34; P=0.90, P=0.76). Conclusions: Our study found that RM is a poor prognostic factor in pathological T1-3N0M0 RC. However, AT does not appear necessary to improve survival outcomes of pathological T1-3N0M0 RM.