Anorectal melanoma manifesting with bone metastases: A clinico-pathological surprise

• Author Details:   
• Ankita Singh
• Anshima Singh ^*
• Asmita Arya

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Anorectal melanoma is a rare malignancy that is known to metastasize in the liver, followed by the lungs. Very rarely it can metastasize into bone, like in our case, which was an elderly man presenting to us with lower back pain and was thus clinically thought to be a case of metastatic prostatic carcinoma. However, radiological details and histopathological examination of the bone marrow biopsy revealed it to be anorectal melanoma with bone metastasis.

A 65-year-old male presented with lower backache for four months. Radiological imaging revealed marrow lesions in the lumbosacral-iliac region and right femur head. A bone marrow biopsy was performed. Its examination revealed sheets of markedly pleomorphic tumor cells containing brownish-black intra-cytoplasmic pigment suggesting metastatic deposits of melanoma. Immunohistochemistry further confirmed the diagnosis. The diagnosis of metastatic melanoma was rendered. Further workup disclosed the primary to be in the anorectal region. Thus, the case was concluded to be that of anorectal melanoma metastasizing to bone.