Adjuvant chemotherapy improves long-term survival in pathologic stage III rectal mucinous adenocarcinoma after pre-operative chemoradiotherapy

Purpose The benefits of adjuvant chemotherapy remain debated rectal mucinous adenocarcinoma (MC). Our study aims to delve into the efficacy of adjuvant chemotherapy in pathologic stage III rectal MC by a large population-based database. Methods The Chi-square test was performed to examine the parameters between treatment groups. The overall survival (OS) and cancer-specific survival (CSS) of treatment groups were conducted by using the Kaplan–Meier method. The impact of factors on survival was assessed using Cox regression analyses. To balance the covariates and reduce the selection bias, we employed propensity score matching (PSM) to narrow the differences between treatment groups. Results The median follow-up time for overall patients was 80 months. In the pre-operative chemoradiotherapy (pre-CRT) group, patients who received adjuvant chemotherapy had significantly better 5-year OS and CSS. Multivariate analyses found that adjuvant chemotherapy was associated with better OS ( p < 0.001, HR (95% CI): 0.66 (0.51–0.86)) and CSS ( p = 0.012, HR (95% CI): 0.71 (0.54–0.93)). However, adjuvant chemotherapy was not an independent prognosis factor in both OS ( p = 0.149, HR (95% CI): 0.76 (0.53–1.1); Supplement Table 1 ) and CSS ( p = 0.183, HR (95% CI): 0.74 (0.48–1.15)) in patients who did not receive pre-CRT. After PSM, similar results were found in the pre-CRT and the no pre-CRT groups. Conclusion In conclusion, our population-based retrospective cohort study indicates that the effects of adjuvant chemotherapy were associated with the pre-CRT status in patients with stage III rectal MC. In patients who underwent pre-CRT, the receipt of adjuvant chemotherapy was associated with better survival outcomes. Conversely, adjuvant chemotherapy does not seem to confer significant survival benefits to patients without pre-CRT.