S6095 A Case of Metastatic Melanoma Masquerading as Small Bowel Intussusception

Introduction: Anorectal melanoma is rare, often diagnosed with advanced disease at presentation. Metastatic spread to the small bowel may result in complications like intussusception. Herein, we report a case of metastatic anorectal melanoma initially presenting as rectal bleeding. Case Description/Methods: A 67-year-old hispanic woman with history of endometrial cancer status post total abdominal hysterectomy and bilateral salpingo-oopherectomy presented to the emergency department (ED) with 1 day of bright red blood per rectum. Over 3 months, she had a 20-pound weight loss, constipation, rectal pain, and low appetite. She never had an endoscopy or colonoscopy. She denied prior bleeding, smoking, or alcohol use. She was febrile (101.2°F) with a body mass index of 20.3. Labs showed hemoglobin 8.3, MCV 87.5; other labs were unremarkable. The abdomen was soft, non-tender and non-distended. Rectal exam revealed a large, beefy, tender mass without active bleeding. Computed tomography showed an entero-enteric intussusception with a 3.5 × 3.6 cm mass and regional lymphadenopathy. Explorative laparotomy found metastatic melanoma in 4 small bowel nodules and 9/14 lymph nodes. Hemorrhoidectomy showed malignant melanoma with positive margins. PET showed a hypermetabolic anorectal mass; brain MRI showed 3 enhancing lesions, largest 2.9 × 1.9 × 2.4 cm in the right temporal lobe with mild mass effect. She began ipilimumab and nivolumab every 3 weeks ×4 cycles, with positron emission tomography showing decreased anorectal and brain lesions size. Discussion: Melanoma makes up only ∼1% of skin cancers, but causes most skin cancer deaths. Adults in the United States (US) have a 2.2% lifetime risk. While global mortality has declined, US rates only modestly improved, likely due to rising cases in high risk groups. Anorectal melanoma is rare (<1.2% of melanomas), usually diagnosed in the mid-60's, with slight female predominance. It often presents as rectal bleeding and is frequently misdiagnosed, delaying detection. Metastases commonly involve lymph nodes, lung, and liver; small bowel is less common and later. About 27% of intestinal metastases present with obstruction or intussusception, usually from cutaneous, not mucosal, primaries. These can be life-threatening and need prompt care. For metastatic anorectal melanoma, the CheckMate 067 trial supports combined immunotherapy with ipilimumab and nivolumab, followed by nivolumab maintenance. This improves survival despite lower response rates in mucosal vs cutaneous melanoma.