Primary anorectal melanotic melanoma: a case report

Anorectal melanoma (AM) is a rare and aggressive malignancy that is often advanced at the time of diagnosis. This case demonstrates the importance of a prompt colonoscopic evaluation, especially in older patients presenting with new gastrointestinal symptoms, and underscores the need for further research establishing a standardized treatment protocol.

We report a case of a 71-year-old white male who was referred to gastroenterology after noticing increased frequency of bright red blood per rectum following bowel movements. A subsequent colonoscopy revealed a 1.5-cm darkly pigmented, irregular mass in the anorectal region. The lesion was excised and sent for microscopic evaluation which disclosed highly malignant spindle and epithelioid cells producing a large amount of brown pigment. A diagnosis of anorectal melanoma was confirmed with positive immunohistochemical staining for S-100, HMB45, and Melan-A. A computed tomography (CT) scan of the abdomen and pelvis showed no evidence of metastasis. The patient then underwent a transanal resection of the area where the tumor was found. No residual melanoma was seen in the resected specimen. Follow-up evaluations over about 2 years have shown no evidence of recurrence.

The positive outcome of this case highlights the importance of timely recognition as well as the ongoing need to explore and refine effective treatment options for AM.