Epidemiology and outcomes of anorectal melanomas: A national database analysis.

e21572 Background: Anorectal melanoma is a rare but aggressive type of melanoma, arising primarily from the mucosal epithelium from the anorectal tract. Knowledge of this rare etiology has been limited given its low incidence. This study aims to characterize the epidemiology and treatment outcomes of anorectal melanoma using a national database. Methods: The Surveillance, Epidemiology and End Results (SEER) Database was queried to identify patients with biopsy-proven anorectal melanoma. The following information was retrieved: tumor site, grade, stage, intervention, lymph node histology, and survival information for oncology codes as per the international classification of diseases. Statistical analysis was performed with Stata 15.1 (STATA Corp., College Station, TX, USA). Results: The age-adjusted anorectal melanoma annual incidence rates have been stable approximately 0.4-0.5 per 1 million from 2000 to 2019. Of the 823 biopsy-proven confirmed cases of anorectal melanoma from 2000 to 2018, 150 (18.2%) received chemotherapy, 182 (22.1%) received radiotherapy, 55 (6.7%) received chemoradiation, while 619 (75.2%) of the population received surgery alone or combined with chemotherapy and/or radiotherapy. Statistically significant improvement in survival was noted in treatment strategies that utilized surgery with and without chemotherapy and/or radiotherapy (median survival time 22 vs 9 months, p < 0.0001). Patients with positive regional lymph nodes on pathology were associated with worse prognosis (median survival time 15 vs 37 months, p < 0.0001). Outcomes did not differ based on sex (p = 0.810) and race (p = 0.372). Conclusions: Incidence of anorectal melanoma in the United States has been stable in the last twenty years. Treatment strategies including surgical resection should be adopted if possible to achieve improved survival outcomes.