Anorectal Melanoma: An Uncommon Cause of Lower Gastrointestinal Bleeding

Anorectal melanoma (ARM) is a rare, aggressive disease. Given that it presents with local symptoms that resemble other common benign anorectal conditions, ARM is often low on the differential diagnosis. Delayed diagnosis and nonconsensus of treatment options lead to poor prognosis. Here, we report the case of an 85-year-old woman with a history of Irritable bowel syndrome who presented with altered bowel habits and bleeding per rectum. CT revealed a rectal mass with metastatic lesions to the bone, liver, and lungs. Immunohistochemical staining was positive for Human Melanoma Black-45, melanoma antigen recognized by T cells, and SRY-related HMG-box 10. A final diagnosis of ARM was made.