EP142 - Anorectal Melanoma: A Rare But Aggressive Mucosal Malignancy

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Purpose/Background: Anorectal melanoma is a rarely encountered but extremely aggressive disease with a poor prognosis. Anorectal melanoma is most commonly found in women over the age of 50, and accounts for 0.4-1.6% of all melanomas and 1% of anorectal malignant tumors. Vague symptomatology and delay to diagnosis, often via misdiagnosis, can lead to advanced-stage disease when discovered. Patients most commonly present with symptoms that mimic various diseases of the anorectal canal and can lead to delayed treatment. Due to its rarity, anorectal melanoma is often misdiagnosed as advanced hemorrhoidal disease and is often discovered on screening endoscopy. One study estimated approximately 60% of cases held a delayed diagnosis, with cases originally diagnosed as hemorrhoidal disease leading to a decrease in median survival from 14 to 6 months. A recent meta-analysis compared nearly 1,900 patients across various studies diagnosed with anorectal melanoma and found that there was no survival benefit independent of tumor stage between patients undergoing local versus extensive resection.

Methods/Interventions: An 85-year-old male with a PMH of COPD, BPH, hyperlipidemia, and depression presented to the colorectal clinic after colonoscopy was completed for hematochezia and a palpable anal mass. The patient reported a 15lb weight loss, decreased appetite, and worsened fecal incontinence. Endoscopy revealed an infiltrating non-obstructing, prolapsing rectal mass. The mass was biopsied but non-diagnostic. Due to his desire for symptomatic relief, the patient elected to undergo transanal mass excision.

Results/Outcomes: The patient underwent anal exam under anesthesia during which a 4x5cm pedunculated mass with a wide base was identified at the right, anterior aspect of the anal canal approximately 1cm from the anal verge. The mass was completely excised with pathology subsequently confirming malignant melanoma. The patient elected to forego further treatment. Four months after resection, the patient was admitted to the ICU for pneumonia with subsequent clinical deterioration, and he unfortunately succumbed to his illness.

Conclusion/Discussion: There is currently no consensus on the best treatment for anorectal melanoma. It is a rare, aggressive disease with studies finding that more aggressive treatment does not necessarily lead to improved survival. Due to recent trends and significant variations in treatment modalities, many have recommended a treatment approach that incorporates surgical excision while minimizing associated morbidity.4,5 A relative scarcity of research into the treatment of this rare disease has led to a lack of a consensus on how to best treat and manage this disease. Greater attention to this disease process may lead to increased survival for those afflicted by this uncommon disease.