Comparative Survival of Patients With Anal Adenocarcinoma, Squamous Cell Carcinoma of the Anus, and Rectal Adenocarcinoma

Abstract

BackgroundAnal adenocarcinoma (AA) represents 5% to 10% of anal cancer. Little is known about its natural history and prognosis. Using population-based data, we defined the outcomes of AA relative to other anorectal malignancies. Patients and MethodsWe analyzed the Surveillance, Epidemiology, and End Results 18 database to identify patients ≥ 18 years old with AA, squamous cell carcinoma of the anus (SCCA), and rectal adenocarcinoma (RA) diagnosed between 1990 and 2011. Median overall survival (OS), 1-year, 3-year, 5-year, and 10-year OS were computed using actuarial methods. The log rank test was used to estimate the difference between Kaplan–Meier survival curves. A Cox proportional hazard regression model was used to adjust the effects of other covariates on survival, including age, year diagnosed, sex, stage, surgery, and radiation. ResultsOf 57,369 cases, 0.8% (n = 462) were patients with AA, 87.8% (n = 50,382) were patients with RA, and 11.4% (n = 6525) were patients with SCCA. The median age for AA was 69 years (range, 20-96 years), 66 years (range, 18-103 years) for RA, and 66 years (range, 14-104 years) for SCCA. The median OS was significantly lower for AA (33 months), compared with SCCA (118 months) and RA (68 months) (P < .01). In multivariate analysis, AA had a worse prognosis compared with SCCA (hazard ratio [HR], 0.66; 95% confidence interval [CI], 0.59-0.75; P < .01) and RA (HR, 0.68; 95% CI, 0.61-0.77; P < .01), after adjusting for age, sex, race, stage, grade, radiation, and surgery. There was a strong trend for improved survival among patients who received radical surgery (HR, 0.71; 95% CI, 0.51-1.00; P = .05). ConclusionAA confers a significantly worse prognosis than SCCA and RA.