S6432 Presumed Gastric Mucosal Melanoma Presenting as Melena and Severe Anemia

Introduction: Primary malignant melanoma of the gastrointestinal (GI) tract is rare, and the stomach is an especially uncommon site. Most GI melanomas are metastatic, typically arising from cutaneous, ocular, or anorectal origins. Primary gastric mucosal melanoma poses a diagnostic challenge given its rarity and vague presentation, leading to delayed diagnosis and poor prognosis. Case Description/Methods: A 60-year-old man with no significant medical history presented to the emergency department with a 1-month history of melena, progressive exertional fatigue, lip pallor, and bilateral leg edema. He denied unintentional weight loss, malignancy, and relevant family history. Labs revealed microcytic anemia with a hemoglobin of 5 g/dL. Imaging of the chest, abdomen, and pelvis showed an 8.2 cm mass-like consolidation in the left lower lobe, a large ulcerating gastric mass abutting the pancreas, lymphadenopathy, mesenteric and peritoneal implants, and osseous metasases. Esophagogastroduodenoscopy demonstrated a large, friable, deeply ulcerated, malignant-appearing lesion located 2 cm from the gastroesophageal junction and involving three-fourths of the proximal stomach. Biopsies confirmed malignant melanoma. The patient elected hospice care and further genetic profiling was not pursued. Based on the lesion's location and lack of an identifiable primary source, findings were consistent with gastric mucosal melanoma. Discussion: Gastric melanoma is rare and typically metastatic. Although most melanomas are cutaneous, the absence of a primary lesion along with the tumor's location and morphology raised suspicion for a mucosal origin. Definitive classification was limited by the lack of full-body skin, ocular, and anorectal exams and the patient's decision to forgo further evaluation. This case highlights melanoma as a differential for upper GI bleeding and ulcerating gastric lesions. While cutaneous melanoma accounts for over 90% of melanomas, skin examinations are often overlooked in patients with isolated GI symptoms. Clinicians should consider rare malignancies in patients with anemia and nonspecific GI symptoms and also include a full-body skin exam in metastatic workup.