What factors are associated with the poor prognosis of anal adenocarcinoma compared with low-lying rectal adenocarcinoma based on a population analysis: A propensity score matching study

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.