Rectal Melanoma: An Uncommon Cause of Hematochezia

Abstract

Purpose: A 91-year-old female presented with acute onset of hematochezia. She was undergoing rehabilitation for cerebrovascular accident that resulted in right hemiparesis. No previous gastrointestinal pathology was reported, and no previous colonoscopy had been performed. Flexible sigmoidoscopy was performed. Endoscopy revealed a 3-cm, exophytic, necrotic, firm mass located at the anorectal verge. Pathology confirmed malignant melanoma, which was S-100 negative, melanin A positive, and HMB-45 positive. Staging CT scan of the abdomen/pelvis showed a mass in the anorectal junction, a pathologically enlarged lymph node in the right axilla, and no retroperitoneal adenopathy, consistent with stage IV malignant melanoma. Given her advanced age, she was determined to be a poor candidate for surgery, and was advised 3 months of palliative radiation therapy. She tolerated the radiation fairly well, and after completion of her treatment, no further rectal bleeding was reported. She deferred repeat endoscopic examination. Discussion: Malignant melanoma of the rectum is a rare entity with poor prognosis. It typically presents in the fifth to sixth decade of life with female predominance. Reported incidence is 0.4-3.0% of all malignant melanomas, and 0.1-4.6% of all anorectal malignant tumors. Malignant melanomas occur frequently in the anorectum region because of the presence of abundant melanocytes in the mucosa of the anal canal. Depth of invasion and stage of the disease are the main prognostic indicators of disease severity. Initial symptoms are rectal bleeding and/or pain, hence confusing the diagnosis with that of hemorrhoids. Early stage detection is important due to rapid progression. Malignant melanoma has been accompanied by distant metastases in 60% of patients at the time of final diagnosis. For anorectal malignant melanoma, multimodality treatments including surgery, chemotherapy, and radiotherapy. The effectiveness of any treatment largely depends on the stage of the melanoma. This case highlights the importance of timely colonoscopic exams for colorectal neoplasm prevention.Figure