Primary anorectal melanotic melanoma: a case report

BACKGROUND: 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. CASE PRESENTATION: 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. CONCLUSIONS: 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.