Purpose: Anal adenocarcinoma (AA) represents a rare condition, and little is known about the predictive factors of the outcomes or the optimal TNM staging system for curable AA. Using population-based data, we preliminarily sought to determine the prognostic factors and evaluate the existing T and N staging criteria of AA.
Methods: We analyzed the Surveillance, Epidemiology, and End Results 18 database to identify patients 20-80 years old who were diagnosed with AA or rectal adenocarcinoma (RA) and underwent abdominal perineal resection between 2004 and 2012. The difference between Kaplan-Meier survival curves was estimated by a log-rank test. A Cox proportional hazard regression model was used to adjust the effects of other covariates on survival in the propensity score-matched cohort, including age, gender, race, marital status, histology, grade of differentiation, tumor size, number of positive lymph nodes, radiotherapy, and chemotherapy.
Results: Compared to patients with RA, patients with AA had a worse CSS after controlling for other covariates (hazard ratio [HR], 1.96; 95% confidence interval [CI], 1.25-3.07; P<0.01). For AA, the increasing tumor size (2-5 cm: HR, 0.62; 95% CI, 0.29-1.32; P>0.05; >5 cm: HR, 1.01; 95% CI, 0.49-2.07; P>0.05) had no significant influence on survival. The number of positive lymph nodes (1-3: HR, 2.93; 95% CI, 1.55-5.53; P<0.01; ≥4: HR, 4.24; 95% CI, 2.08-8.62; P<0.01) significantly influenced survival.
Conclusions: AA confers a worse prognosis than RA does. The T staging criteria of anal carcinoma, dominated by tumor size, seem to be invalid for AA, while the number of positive lymph nodes is a prognostic factor.