Background: Chemoradiotherapy (CRT), the primary treatment for anal cancer, achieves complete tumor regression in most patients. Abdominoperineal resection (APR) is reserved for persistent or recurrent disease. An additional boost dose of radiation after CRT often is used to improve the response rate for advanced local disease (T3, 4, and N+). This study examines the need for salvage APR after radiation boost. Methods: Patients with de novo anal cancer in the National Cancer Data Base from the years 2004–2010 were analyzed. Patients with missing data points or who did not receive standard CRT were excluded. Variables included age, gender, race, primary tumor size, clinical nodal status, TNM stage, radiation boost, and APR. A logistic regression model assessing the relationship between boost radiation and APR was developed. Results: Of 1,025 patients meeting inclusion criteria, 450 patients received CRT without a radiation boost and 575 patients received CRT with a radiation boost. The two groups were similar in age, gender, race, tumor size, nodal status, and TNM stage (p values all >0.05). Significant multivariate predictors of salvage APR were tumor size, negative nodal status, and boost RT (all p < 0.05), whereas gender, age, race, and TNM stage were not significant (all p > 0.05). When controlling for age, tumor size, and nodal status, salvage APR is less likely to occur after boost RT (odds ratio 0.63; 95 % confidence interval 0.47, 0.85; p = 0.003). Conclusions: When controlling for age, tumor size, and nodal status, those who received boost radiation for anal cancer were less likely to require salvage APR.
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