Anal Canal Adenocarcinomas: Prognostic Factors and Outcomes at a Single Institution

Abstract

Adenocarcinomas of the anal canal (AAC) represent a rarity among cancers of the digestive tract. Data guiding management is limited to retrospective studies and optimal treatment paradigms of AAC are still evolving. Here, we aim to investigate their prognostic factors and outcomes. We reviewed anorectal adenocarcinoma patients who underwent curative-intent neo/adjuvant therapy +/- surgery at a single institution from 2015-2019. AAC were defined as tumor epicenters ≤ 2 cm from the dentate line. Our primary outcome was 5-year overall survival (OS). We also analyzed 5-year local recurrence, distant metastasis, and disease-free survival (DFS), defined as the interval after treatment completion to the first occurrence of local, regional, distant recurrence, or death. All tumors were staged according to the Rectal Cancer paradigm per AJCC 7th Staging. Kaplan-Meier and Cox-Proportional Hazards Model were used for survival analyses. In our cohort, 57 patients met inclusion criteria. Median follow-up time was 54 months. The median age was 64 years; 35% of the cohort was female. The majority of tumors were adenocarcinomas (77%), with a minority of mucinous (12%) and signet ring cell (11%) histologies. The median tumor size was 4 cm, located 1 cm from the anal verge. Most tumors (63%) were grade 2, 77% had T3 disease, and 53% had clinical nodal involvement. Most patients completed neoadjuvant chemoradiation, total mesorectal excision, and adjuvant chemotherapy (54%). Fifty-four percent underwent abdominopelvic resection. Of those who received neoadjuvant therapy, 11% achieved a pathologic complete response. Seventy percent of patients completed chemotherapy, either in the neoadjuvant or adjuvant setting. At 5 years, local recurrence was 9%, regional pelvic recurrence was 12%, inguinal nodal recurrence was 2%, and distant recurrence was 25%. Five-year DFS was 63% and 5-year OS was 70%. Multivariate analysis demonstrated age, female gender, CEA, grade 3 disease, mucinous histology, and nodal involvement to be prognostic of lower OS. Receipt of neo/adjuvant chemotherapy was found to be prognostic of higher OS (HR 0.13, p<0.05). In this cohort, the majority of whom received surgical management, we show numerically similar or higher overall survival in comparison with prior studies. This study is limited by its retrospective nature and sample sizes of an exceedingly rare entity. Receipt of neo/adjuvant chemotherapy appears to have an impact on survival. Further investigation is needed to explore the role of total neoadjuvant therapy in improving outcomes in this patient population.