Background Previous studies have reported that 30% to 40% of patients with squamous cell carcinoma of the anus will require salvage abdominoperineal resection after chemoradiotherapy. Objective The purpose of this study was to identify the use, risk factors, and impact on survival of salvage abdominal perineal resection for squamous cell carcinoma of the anus. Design This was a retrospective, population-based cohort study. Settings Patients treated in Ontario, Canada through a single-payer universal healthcare system, were included. Patients Patients included all incident cases of squamous cell anal cancer who underwent curative intent radiotherapy from 2007 to 2015. Main outcome measures Risk of salvage abdominoperineal resection, factors associated with salvage abdominoperineal resection, and survival were measured. Results A total of 1125 patients were treated with curative intent radiotherapy for squamous cell cancer of the anus. Within this cohort, salvage surgery was performed in 8% (93/1125), whereas 14% (156/1125) required a permanent colostomy. In log-binomial regression, younger age was associated with salvage surgery, whereas sex, cancer stage, socioeconomic status, and HIV were not. There was a suggested lower risk of salvage surgery in those who completed chemoradiation (relative risk = 0.67 (95% CI, 0.43-1.03)). Crude 5-year overall survival rate was 73% (95% CI, 70%-76%) in those not requiring salvage surgery and 48% (95% CI, 37%-58%) in those who did. In Cox models, mortality was higher in patients requiring salvage surgery compared with those who did not (adjusted HR = 2.20 (95% CI, 1.65-2.94), whereas improved survival was seen in those who completed chemoradiation (HR = 0.65 (95% CI, 0.42-0.82)) LIMITATIONS:: The study was limited by its potential residual confounding by indication for salvage surgery. Conclusions In this large, contemporary cohort of patients with squamous cell carcinoma of the anus, the proportion of patients undergoing salvage surgery was considerably lower than previous reports. Younger age was associated with salvage surgery, and there was a suggestion of lower risk of salvage surgery with completion of chemoradiation. Patients requiring salvage surgery had poor 5-year overall survival. See Video Abstract at http://links.lww.com/DCR/B205. RAP DE RESCATE PARA EL CARCINOMA ANAL DE CeLULAS ESCAMOSAS: USO, FACTORES DE RIESGO Y RESULTADOS EN UNA POBLACIoN CANADIENSE: Estudios anteriores han reportado que 30-40% de los pacientes con carcinoma de celulas escamosas del ano requeriran una reseccion abdominoperineal de rescate despues de la quimiorradioterapia.Identificar la utilizacion, los factores de riesgo y el impacto en la supervivencia de la reseccion abdominoperineal de rescate para el carcinoma de celulas escamosas del ano.Estudio de cohorte retrospectivo, basado en la poblacion.Todos los casos incidentes de cancer anal de celulas escamosas que se sometieron a radioterapia con fines curativos de 2007 a 2015.Pacientes tratados en Ontario, Canada, un sistema de salud universal de un solo pagador.Riesgo de reseccion abdominoperineal de rescate, factores asociados con la reseccion abdominoperineal de rescate y la supervivencia.1125 pacientes fueron tratados con radioterapia de intencion curativa para el cancer de celulas escamosas del ano. Dentro de esta cohorte, la cirugia de rescate se realizo en el 8% (93/1125), mientras que el 14% (156/1125) requirio una colostomia permanente. En la regresion log-binomial, la edad mas joven se asocio con la cirugia de rescate, mientras que el sexo, la etapa del cancer, el estado socioeconomico y el VIH no. Se sugirio un menor riesgo de cirugia de rescate en aquellos que completaron la quimiorradiacion (RR 0,67; IC del 95%: 0,43 a 1,03). La tasa de supervivencia global bruta a 5 anos fue del 73% (IC del 95%: 70-76%) en aquellos que no requirieron cirugia de rescate y del 48% (IC del 95%: 37-58%) en los que si lo requirieron. En los modelos de Cox, la mortalidad fue mayor en los pacientes que requirieron cirugia de rescate en comparacion con aquellos que no lo requirieron (HR ajustado 2.20, IC 95%: 1.65 - 2.94), mientras que se observo una mejor supervivencia en aquellos que completaron la quimiorradiacion (HR 0.65, IC 95% 0.42 - 0,82).Posible confusion residual por indicacion de cirugia de rescate.En esta gran cohorte contemporanea de pacientes con carcinoma de celulas escamosas del ano, la proporcion de pacientes sometidos a cirugia de rescate fue considerablemente menor que los informes anteriores. La edad mas temprana se asocio con la cirugia de rescate, y se sugirio un menor riesgo de cirugia de rescate con la finalizacion de la quimiorradiacion. Los pacientes que requirieron cirugia de rescate tuvieron una deficiente supervivencia general de 5 anos. Consulte Video Resumen en http://links.lww.com/DCR/B205. (Traduccion-Dr Gonzalo Hagerman).