S6165 Metastatic Amelanotic Melanoma: An Unusual Cause of Gastrointestinal Bleeding and Intussusception

Introduction: Amelanotic melanoma is a rare subtype of melanoma lacking melanin pigmentation, accounting for 2%–8% of cases. Its atypical, non-pigmented presentation often leads to delayed diagnosis. Although melanoma commonly metastasizes to the gastrointestinal (GI) tract, these metastases are clinically detected in only 1–4% of cases due to nonspecific or absent symptoms. Small bowel intussusception is an uncommon cause of intestinal obstruction in adults, with neoplasms responsible in 65% of cases; however, melanoma metastases as the lead point are rarely reported. Similarly, GI bleeding as a presenting feature of metastatic melanoma is uncommon. We present a rare case of metastatic amelanotic melanoma in a patient without a known melanoma history, presenting with both GI bleeding and small bowel obstruction due to intussusception. Case Description/Methods: A 60-year-old previously healthy man presented with fatigue, dizziness, exertional dyspnea, and melena. Laboratory evaluation revealed severe anemia (Hb 4.4 g/dL), prompting multiple transfusions. Computed tomography imaging showed 2 small bowel masses, 1 causing small bowel-small bowel intussusception with partial obstruction. He underwent exploratory laparotomy with jejunal segment resection and lymph node excision. Pathology revealed a spindle cell neoplasm; further evaluation with computed tomography chest showed left axillary lymphadenopathy, and biopsy confirmed similar histology. He was discharged postoperatively with a differential diagnosis of amelanotic melanoma versus clear cell sarcoma. On follow-up, a growing skin lesion on the left flank was identified as the likely primary. Positron emission tomography scan revealed hypermetabolic activity in the left axilla, gastric region, and the flank lesion. The final diagnosis was metastatic stage IV amelanotic melanoma (TxN3bM1c) with an NRAS mutation and no BRAF mutation. The patient was initiated on combination immunotherapy with nivolumab and ipilimumab for systemic disease management. Discussion: This case highlights the diagnostic challenges of amelanotic melanoma, a non-pigmented variant that often presents atypically and leads to delayed diagnosis. The simultaneous occurrence of gastrointestinal (GI) bleeding and small bowel intussusception as initial manifestations of metastatic melanoma is exceptionally rare. In the absence of a known melanoma history or visible pigmentation, identifying the primary lesion can be difficult. This case emphasizes the importance of maintaining a high index of suspicion for melanoma in unusual GI presentations.