Malignant Melanoma of the Anorectal Region: A Case Study and Review of the Contemporary Treatment Options

Aims: Anorectal melanoma, an uncommon malignancy of mucosal origin accounts for 0.05 per cent of all colorectal malignancies and 1 per cent of tumours of the anal canal. The typical clinical presentation includes local pain, palpable mass, bleeding, change in bowel habits, and weight loss. The symptoms are somewhat nondescript and unremarkable and can be easily confused with other conditions native to the region. Hence, a careful and timely assessment is imperative in treating this condition.

Presentation of Case: A case involving a 54-year-old male who presented with a 3-month history of rectal bleeding and pain. Further assessment revealed a malignant melanoma of the anal canal. After undergoing laparoscopic abdominoperineal resection, the patient was on 6 cycles of dacarbazine. He was subsequently found to have liver metastasis. He subsequently started oral Temozolomide for 2 cycles. He has been on close follow-up for the last 6 months and the disease has not progressed since.

Discussion: The course of evaluation in suspected cases of anorectal melanoma is a rectal examination, biopsy and histopathologic examination. Immunohistochemistry aids in the confirmation of the diagnosis. Laparoscopic abdominoperineal resection demonstrates good response rates. Adjuvant chemotherapy in anorectal melanoma can be given in patients following surgical resection of the primary anorectal tumour and with a high risk of recurrence. Targeted therapies like c-kit inhibitors, BRAF inhibitors, anti- CTLA-4 antibodies and anti-PD-1 antibodies can also be used.

Conclusion: Melanomas of the anorectal region present a diagnostic dilemma and carry poor prognoses. Despite an aggressive management approach, the disease maintains an average five-year survival rate of 20%.