Survival outcomes of anal adenocarcinoma versus rectal adenocarcinoma: A retrospective cohort study

Abstract

Background: Anal adenocarcinoma (AA) is a rare malignancy with decreased survival compared to rectal adenocarcinoma (RA). However, AA continues to be treated with similar algorithms compared to rectal cancer with minimal data regarding the efficacy of these treatment algorithms.

Methods: A retrospective chart review of patients with non-metastatic AA at a single tertiary-care institution from 1995 to 2020. This cohort was matched 2:1 to a group of RA patients for comparison. The primary outcome of interest was overall survival rates.

Results: Sixteen patients with stages I-III AA were matched to a cohort of RA. There were no significant differences between the cohorts with regard to patient demographics, comorbidities, disease stage or histologic features. There were also no significant differences in treatment modalities between the two cohorts with a majority undergoing multimodal therapy with chemoradiation and surgery. All patients with AA demonstrated significantly worse survival than all patients with rectal adenocarcinoma (five-year survival 47.7% vs. 82.3%, respectively. p < 0.05). When looking at a sub-group of patients who underwent combination chemoradiation and surgery from each cohort, anal adenocarcinoma continued to exhibit lower overall survival (five-year survival 41.6% and 86.4%, respectively. p < 0.05). In a multi-variable model that adjusted for location, American Joint Committee on Cancer (AJCC) stage and treatment pathway, tumor location in the anal canal was an independent predictor of overall survival (Hazard ratio [HR] 2.7, p < 0.05).

Conclusion: AA has worse survival as compared to RA despite similar treatment. This study highlights the need to evaluate the current classification and treatment pathways to improve outcomes.

Keywords: Anal adenocarcinoma; Anal cancer; Chemoradiation therapy; Multimodal therapy; Rectal adenocarcinoma; Surgical resection; Survival outcomes.