Primary anorectal malignant melanoma: A case report.

Introduction: Anorectal malignant melanoma (AMM) is a rare and aggressive malignance with poor prognosis, yet no consensus of treatment exists to date. Abdominoperineal resection surgery (APR) is the standard treatment of anorectal malignant melanoma, capable of controlling lymphatic spread and obtaining a large negative margin for local control but it can lead to complications. Wide local excision (WLE) allows for quicker recovery and has minimal impact on bowel function (i.e., bypassing the need for a stoma).

Patient Concerns: A 66-year-old male patient presented with a 2-months history of painless rectal bleeding.

Diagnosis: The characteristic finding from colonoscopy and magnetic resonance imaging led to a diagnosis of colorectal cancer. Immunohistochemistry analyses confirmed malignant melanoma. The tumor was classified as: HMB-45(+), S-100(+), CD117(±), PCK(-), ki-67(+, 10%).

Interventions: The patient underwent abdominoperineal resection with no other adjuvant therapy.

Outcomes: The patient is doing well at 24 month after the operation, with no signs of recurrence.

Conclusion: AMM is a rare malignance, and is easy to misdiagnose. The therapy approach remains controversial. Every effort should be made to ensure prompt diagnosis and to define the optimally effective standard therapy approach.