Detection and surgical intervention in anorectal malignant melanoma: a case report

Anorectal malignant melanoma (ARMM), a rare and highly aggressive subtype of mucosal melanoma, accounts for < 0.1% of all colorectal malignancies. Characterized by nonspecific clinical manifestations and the absence of early diagnostic biomarkers, ARMM is frequently diagnosed at advanced stages, resulting in a dismal prognosis with a 5-year survival rate below 20%. Despite recent advances in immunotherapy and targeted therapies, critical knowledge gaps persist regarding its pathogenesis, standardized therapeutic protocols, and prognostic prediction models.

We present a case of a 54-year-old Chinese female patient who was referred to our hospital with a two-month history of rectal bleeding secondary to altered bowel habits. On digital rectal examination, a mass measuring approximately 3 cm in diameter was palpated on the left lateral wall of the rectum, which was located 3.2 cm from the anal verge. Endoscopy revealed a protruding lesion. Histopathological examination of the biopsy samples confirmed the diagnosis of ARMM. Comprehensive staging with computed tomography and magnetic resonance imaging revealed no locoregional or distant metastases. The patient underwent abdominoperineal resection, which proceeded without complications. The definitive diagnosis was malignant melanoma of the lower anal canal, at stage T2aN0M0, I B. During the six months follow-up period, there was no evidence of tumor recurrence or long-term postoperative complications in the patient.

This case underscores the importance of early diagnosis and appropriate management of anorectal malignant melanoma to optimize patient outcomes.