Neoadjuvant concurrent chemoradiation (CCRT) is standard treatment for clinical stage II/III rectal cancers. However, whether patients with pathological complete response (pT0N0, pCR) should receive adjuvant chemotherapy and whether delayed surgery will influence the pCR rate remains controversial. A nationwide population study was conducted using the Taiwan Cancer Registry Database from January 2007 to December 2013. Kaplan-Meier survival analysis was performed. Cox proportional hazards models were used to estimate multivariate adjusted hazard ratios (HR) and 95% confidence intervals (95% CI). Of the 1,914 patients who received neoadjuvant CCRT, 259 (13.6%) achieved pCR and had better survival (adjusted HR: 0.37, 95% CI: 0.24-0.58; p < 0.001). The cumulative rate of pCR rose up to 83.4% in the 9th week and slowly reached a plateau after the 11th week. Among the patients with pCR, those who received adjuvant chemotherapy had no survival benefits compared to those without adjuvant chemotherapy (adjusted HR: 0.72, 95 CI: 0.27–1.93; p = 0.52). By subgroup analysis, those younger than 70-year old and received adjuvant chemotherapy had better survival benefit than those without adjuvant chemotherapy (adjusted HR: 0.19, 95% CI: 0.04–0.97; p = 0.046). Delayed surgery by 9–12 weeks after the end of neoadjuvant CCRT can maximize the pCR rate, which is correlated with better survival. Adjuvant chemotherapy may be considered in patients with pCR and aged <70-year old, but further prospectively randomized controlled trials are warranted to validate these findings.
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