Oncological strategy following R1 sphincter-saving resection in low rectal cancer after chemoradiotherapy.

Aim: Sphincter-saving resection (SSR) for low rectal cancer remains challenging due to the high risk of positive resection margin (R1). Long-term outcomes and the dedicated oncological strategy are not well established in this situation. The aim of this study was to define the more appropriate strategy according to the patterns of recurrence.

Methods: Between 1994 and 2014, patients treated by SSR for low rectal cancer with preoperative chemoradiotherapy were included. Three types of recurrences were defined: local (LR), distant (DR) and mixed (MR). Recurrences and survival after R0 and R1 resection were analysed by Kaplan-Meier and compared with the log-rang test.

Results: Among 394 patients receiving SSR, 42 (10.6%) had R1 resection. Independent factors of R1 resection were EMVI (OR2.24,95%IC1.10-4.53,p = 0.025) and no tumor downstaging (OR8.41,95%IC2.50-8.32,p = 0.001). Both 5-year disease free and overall survival, and 5-year distant and local recurrence, were significantly worse after R1 resection. The overall recurrence after R1 resection was 57% (24/42), 7% had LR, 36% DR and 14% MR. Time to DR was shorter than time to LR (11.1 vs. 34.3) months. In all cases of MR, DR occurred before LR (12.1 vs. 34.3) months, meaning that after R1 resection, the first concern was DR.

Conclusion: R1 resection after SSR for low rectal cancer reflects a more aggressive and systemic disease. Prognosis depends on DR in about 90% of cases, suggesting that pelvic control should not be the priority in the oncological strategy after R1. Adjuvant systemic chemotherapy ought to be preferred to salvage abdominoperineal resection.