Unusual presentation and course of malignant melanoma of anal canal in an African-American patient

Background

While cutaneous melanoma is common in up to 2.6% of Caucasian population, it is far less common in the African American population, up to 0.1%. Additionally, anal melanoma in particular comprises less than 1% of all melanomas and roughly 4% of anal cancers, while Spindle-cell variants are even less common, suggesting an extremely low incidence in the African American population. Definitive diagnosis can be challenging due to lack of definitive mass or pigmentation at presentation. There is a lack of good long-term studies and treatment guidelines for this malignancy with significant variation in treatment approaches and patient outcomes.

Case description

Here we present a case of an 63-year old African American gentleman with no significant past medical history and unremarkable colonoscopy 3 years prior, who presented with a mass in the anal canal that was found during a scheduled screening colonoscopy. The patient was completely asymptomatic at presentation. PET/CT scan showed hypermetabolic activity in the anal canal region. Patient underwent surgical excision with pathology revealing a 2.7 cm spindle cell type of malignant melanoma and promptly treated with adjuvant immunotherapy, resulting in extended progression-free survival before recurrence in the liver.

Conclusion

The early diagnosis of spindle cell melanoma can prompt more aggressive surgical and systemic management options resulting in extended survival, however, late recurrences are common and often refractory to standard therapeutic options.