A 22-year experience of surgical management of anorectal melanoma: risk factors for recurrence and death

Purpose: Anorectal melanoma (ARM) poses a significant challenge due to the lack of established guidelines and a 5-year overall survival rate of less than 20%. The only recognized death risk factors are positive lymph nodes and positive surgical margins. This study aimed to identify the risk factors for local/distant recurrences and death in a 22-year multi-institutional experience. Methods: All patients who underwent curative surgical resection or were referred to after resection at the Mayo Clinic for non-metastatic ARM (2002–2024) were included. Risk factors for local/distant recurrences, and deaths were assessed through multivariable Cox regression. Results: Eighty-eight patients were included in the study. Seventy-eight percent of patients had anal melanoma and 22% rectal melanoma. Nineteen percent had clinically positive lymph nodes. The surgical margins were positive in 62% of local surgeries, while they were positive in 13% of radical surgery cases. The first recurrence was often a local recurrence (67%), followed by distant metastasis (21%), with an overall comparable overall survival between the two. Radiotherapy administration, radical surgery, and negative margins were associated with less local recurrence. Clinically positive lymph nodes and local recurrences increased the risk of developing distant metastasis over time. Clinically negative lymph nodes, radiotherapy administration, radical surgery, and negative margins all contributed to a reduced death risk. Conclusion: Local recurrences in ARM may influence distant metastasis and death more than what was previously believed. Positive surgical margins in local surgery were remarkably high, reaching 62%. Protective factors for local recurrence and death included radical surgery, negative surgical margins, and radiotherapy.