Amelanotic Jejunal Malignant Melanoma Presenting as Overt Small-Bowel Bleeding and Mimicking a Gastrointestinal Stromal Tumor: A Case Report

Background: Small-bowel bleeding accounts for a minority of gastrointestinal hemorrhage and may pose a diagnostic challenge after negative bidirectional endoscopy. Malignant melanoma involving the small intestine is usually metastatic, whereas a true primary small-bowel melanoma is exceptionally rare and remains controversial. Case Report: We report the case of a 76-year-old female patient who presented with severe symptomatic iron-deficiency anemia and recurrent overt gastrointestinal bleeding. Esophagogastroduodenoscopy and colonoscopy did not identify a bleeding source. Cross-sectional imaging demonstrated a large necrotic mass in the inter-gastro-jejunal region, initially interpreted as a possible gastrointestinal stromal tumor (GIST). Endoscopic ultrasound showed a heterogeneous lesion exceeding 100 mm and enabled fine-needle biopsy. Histopathology demonstrated a malignant epithelioid amelanotic melanoma with diffuse SOX10, S100, and Melan-A expression and a high proliferative index. Concomitant CD117 positivity represented a potential diagnostic pitfall given the initial suspicion of a GIST. Enteroscopy subsequently documented a large ulcerated jejunal lesion with friable mucosa and stigmata of recent bleeding, demonstrating luminal involvement and ascertaining it as the likely source of blood loss. Dermatologic and ophthalmologic examinations revealed no alternative primary melanoma. Conclusions: This case illustrates the complementary roles of cross-sectional imaging, EUS-guided tissue acquisition, and enteroscopy in a tumor that mimicked a GIST, while emphasizing that absence of an identifiable extraintestinal primary does not by itself prove a primary intestinal origin.