Adjuvant chemotherapy does not improve cancer-specific survival for pathologic stage II/III rectal adenocarcinoma after neoadjuvant chemoradiotherapy and surgery: evidence based on long-term survival analysis from SEER data.

PURPOSE: Adjuvant chemotherapy is controversial in rectal cancer, especially after neoadjuvant chemoradiotherapy (NCRT). This retrospective study aims at evaluating adjuvant chemotherapy's long-term survival benefits in stage II and stage III rectal adenocarcinoma (RC).

METHODS: This study obtained data from the Surveillance, Epidemiology, and End Results (SEER) database registered between 2010 and 2015. The survival analyses used the Kaplan-Meier method and were compared by log-rank test. The factors that affect survival outcomes were analyzed by univariate and multivariate Cox regression. The propensity score matching (1:4) was used to ensure the balance of variables between different groups.

RESULTS: The median follow-up time for overall patients was 64 months. The 5-year overall survival (OS) and cancer-specific survival (CSS) rates were 51.3% and 67.4% in the adjuvant chemotherapy (-) group and 73.9% and 79.6% in the adjuvant chemotherapy ( +) group (p < 0.001, p = 0.002). However, subgroup analysis showed adjuvant chemotherapy after NCRT improved the 5-year OS but not CSS rates in stage II and stage III RC (p = 0.003, p = 0.004; p = 0.29, p = 0.3). Univariate and multivariate analyses found adjuvant chemotherapy after NCRT was an independent prognosis factor of OS but not CSS (HR 0.8, 95%CI 0.7-0.92, p < 0.001; p = 0.276).

CONCLUSION: The survival benefits from adjuvant chemotherapy were associated with the status of NCRT for pathological stage II and III RC. For patients who did not receive NCRT, adjuvant chemotherapy is needed to significantly improve long-term survival rates. However, adjuvant chemotherapy after NCRT did not significantly improve long-term CSS.