Role of Adjuvant Chemotherapy After Curative Resection in Stage II and III Rectal Cancer

Introduction: Patients with resected locally advanced rectal cancer (LARC) and an incomplete total mesorectal excision (TME) have worse oncologic outcomes. The associations between TME grade, adjuvant therapy receipt, and oncologic outcomes have not been well-studied. We aimed to determine the association between adjuvant chemotherapy and oncologic outcomes in patients who underwent neoadjuvant chemoradiation (CRT) or short-course radiotherapy (SCRT) followed by proctectomy and to evaluate this association stratified by TME grade. Materials and methods: We analyzed a retrospective multi-institutional cohort of primary LARC patients diagnosed between 2010 and 2018 who received neoadjuvant CRT/SCRT followed by proctectomy. Complete TME was defined as complete mesorectal excision, and noncomplete TME was defined as near-complete or incomplete TME. We used adjusted Cox proportional hazards regression to test the association between adjuvant chemotherapy and mortality or locoregional recurrence (LRR) across groups. Results: We identified 746 eligible patients. On final pathology, 101 (13.5%) had noncomplete and 645 (86.5%) had complete TME. Rates of adjuvant chemotherapy receipt were similar between noncomplete and complete TME groups (70.3% and 69.5%, respectively). Mean follow-up interval was 35 mo. Adjuvant chemotherapy was associated with lower risk of mortality (HR 0.27, 95% CI 0.19-0.39, P < 0.001); the same association existed when stratifying patients by TME grade. For patients with a complete TME, adjuvant chemotherapy was associated with lower LRR (HR 0.08, 95% CI 0.01-0.56, P = 0.01). The LRR model for the noncomplete TME group did not converge due to few captured recurrences. Conclusions: These data show an association between adjuvant chemotherapy and positive outcomes in LARC patients receiving neoadjuvant CRT/SCRT followed by proctectomy.