Survival Outcomes and Patterns of Management for Anal Adenocarcinoma

Background: Anal adenocarcinoma (AA) is a rare histologic subtype of anal cancer believed to have worse outcomes than anal squamous cell carcinoma (AS). This study aimed to examine practice patterns and treatment outcomes for this rare subtype using the National Cancer Data Base (NCDB). Methods: Patients who had new diagnoses of anal cancer treated with chemoradiation were selected from the NCDB from 2004 to 2015. The patients were divided into two histologic groups (AA or AS). Statistics included the Chi square test to analyze categorical proportions in demographic information, Kaplan–Meier analysis to evaluate overall survival (OS), and Cox proportional hazards modeling to determine variables associated with OS. Results: The study analyzed 24,461 patients. Compared with AS patients, AA patients were more likely to be male, to present with a higher cancer stage, to be older (> 65 years), and to undergo surgery with an abdominoperineal resection (APR). The median OS was 72.5 months for the AA patients and 143.8 months for the AS patients (P < 0.001). Survival was longer for the AA patients undergoing APR within 6 months after chemoradiation (CRT) than for the AA patients who had an APR 6 months after CRT (88.3 vs. 58.1 months; P < 0.001). In the multivariable analysis, the factors associated with worse survival included adenocarcinoma subtype, age of 55 years or older, male gender, T stage of 3 or higher, comorbidity score of 1 or higher, lower income, and treatment at a nonacademic institution. Conclusions: In this largest study of anal adenocarcinoma to date, trimodality therapy was associated with better survival than chemoradiation alone.