Effect of adjuvant chemotherapy following pathologic complete response on long-term survival in rectal cancer: A propensity score matched analysis.

Abstract

717 Background: The role of adjuvant chemotherapy following resection in patients with rectal cancer that achieve pathologic complete response (pCR) after neoadjuvant therapy is unclear. Current data have been limited by small sample size series. This study examined the impact of adjuvant chemotherapy following pCR on overall survival in a national cohort of patients. Methods: Patients with rectal adenocarcinoma were identified in the National Cancer Data Base between 2006 and 2012. Those with locally advanced tumor (clinical stage II or III) that achieved pCR (defined as ypT0N0 in surgical specimens) after neoadjuvant chemoradiotherapy (nCRT) were included in the study. We matched by propensity score patients that received adjuvant chemotherapy (ACT) and patients that did not receive postoperative treatment (no-ACT) controlling for demographic as well as perioperative patient and tumor characteristics. Overall survival was compared using a Cox proportional hazards model. Results: We identified 2,543 patients (ACT: 732, no-ACT: 1,811 patients) with resected locally advanced rectal adenocarcinoma that achieved pCR after nCRT. Among patients that received ACT, 711 were matched with 711 patients in the no-ACT group. Adjuvant chemotherapy was associated with improved overall survival compared to no-ACT (hazard ratio[HR] = 0.46, 95% confidence interval [CI] = 0.29 – 0.75). Overall survivals at 1, 3, and 5 years in the ACT and no-ACT groups were 100% vs 98% (P=0.1), 98% vs 94% (P<0.01), and 94% vs 89% (P<0.01), respectively. In subgroup analyses, adjuvant chemotherapy improved overall survival in patients with clinical stage II (HR = 0.43, 95% CI = 0.22 – 0.85) as well as stage III tumor (OR = 0.50, 95% CI = 0.26 – 0.98). Among patients that received adjuvant chemotherapy, there was no difference in overall survival between single agent and multiagent regimens (HR = 1.37, 95% CI = 0.57 – 3.29). Conclusions: Adjuvant chemotherapy may providea small long-term survival benefit in patients with resected locally advanced rectal cancer and pCR after nCRT.