Primary Melanoma of the Rectum in an African-American Male

Purpose: Most melanomas of the gastrointestinal (GI) tract are metastases from cutaneous or ocular origin. There have been very few select reports of primary melanomas of the GI tract, and they have been known to have a poor prognosis. We report a case of a 56-year-old African-American male who presented with four kg of weight loss, four months of intermittent hematochezia, rectal discomfort, one month of epigastric pain, and one week of jaundice. Past medical history included a 40-pack-a-year smoking history. There was no personal or family history of cancer. His blood work showed hemoglobin of 12.5 gm/dl (13.5-17.5), MCV 95 (80-100), AST 236 IU/L (15-41),ALT 436 IU/L (17-63), total bilirubin 11.8 mg/dl (0.2-1.2), alkaline phosphatase 215 IU/L (32-91). Abdominal and pelvis computed tomography with contrast showed mild hepatomegaly with intrahepatic and extrahepatic ductal dilation, mildly prominent pancreatic head and uncinate process, non-specific rectal wall thickening up to 1.8 cm, and right adrenal thickening. Endoscopic retrograde cholangiopancreatogram (ERCP) showed multiple 5-20 mm bluish-black ulcers with thickened elevated borders in duodenum, normal ampulla, dilated 25-mm common bile duct (CBD) with 4-mm long apple core-shaped stricture at distal end and intrahepatic ducts dilation. Brush cytology specimen were taken and plastic stent was left in place. Colonoscopy showed a 6-cm long, elevated lesion with ulcerated necrotic center, involving 50% of the circumference, and occupying 80% of the lumen. The lesion was close, but not involving the dentate line. Biopsy of duodenal lesions and rectal mass was compatible with malignant melanoma, extensively involving mucosa and submucosa with tumor cells strongly positive for HMB45 and Melan-A, and weakly positive for S100 immunostain. BRAF and KIT gene mutations were negative. The brushing from the ERCP showed atypical cells compatible with same diagnosis. The biliary obstruction improved after plastic stent, and later, this was exchanged for a partially covered metallic stent with normalization of his total bilirubin. PET scan showed increased uptake in the posterior tongue, small bowel wall, retroperitoneal lymph nodes, adrenals, and rectal wall. ENT visualization of posterior tongue did not find a mass. Dermatology consult did not find any suspicious skin lesions for primary melanoma. Ophthalmology did not find any evidence of intraocular melanoma. The patient was enrolled in a trial with pazopanib and paclitaxel for unresectable melanoma. However, the patient died seven months after his diagnosis. Primary gastrointestinal melanomas are rare tumors with unknown risk factors, very aggressive, and with no proven established treatment.