Anorectal Melanoma with Penile Metastasis: A Rare Manifestation of an Aggressive Malignancy

A 58-year-old male presented with anorectal mass, diagnosed as anorectal melanoma via biopsy and immunohistochemistry. Magnetic resonance imaging revealed local invasion. He underwent laparoscopic abdominoperineal resection. Follow-up 18F- fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) showed metastases to liver, lungs, bone, and notably, soft tissue deposit along the penis—an undocumented site for anorectal melanoma metastasis. Anorectal melanoma is a rare, aggressive malignancy with poor prognosis and limited treatment guidelines. Penile metastasis, though rare in general, has not been previously reported from anorectal melanoma. This case highlights the aggressive nature of the disease and underscores the diagnostic value of 18F-FDG PET/CT in detecting atypical metastases.