S4528 Gastric Bloom: A Rare Case of Flower-Like Lesions in Isolated Gastrointestinal Langerhans Cell Histiocytosis

Introduction: Langerhans cell histiocytosis (LCH) is a rare clonal proliferation of dendritic cells with variable clinical manifestations. Although LCH is typically observed in children and commonly affects the skin, bones, and pituitary gland, it is rare in adults, with isolated involvement of the gastrointestinal (GI) tract being even more uncommon. We present a case of isolated GI-LCH, incidentally discovered in an asymptomatic patient during an esophagogastroduodenoscopy (EGD), highlighting the critical role of endoscopic and histopathological evaluation in identifying subtle and atypical gastric lesions. Case Description/Methods: A 64-year-old otherwise asymptomatic man with a remote history of melanoma and tobacco use disorder was incidentally found to have diffuse esophageal thickening on annual low-dose computerized tomography (CT) of the chest performed for lung cancer screening and was referred to the GI clinic. He reported only occasional heartburn without any other GI symptoms. EGD revealed a normal esophagus, but multiple scattered, small (<5 mm), flower-like lesions in the gastric body and fundus were found. Biopsies demonstrated histiocytic infiltration positive for CD1a and S100 on immunohistochemistry, with confirmation of the BRAF V600E mutation, consistent with LCH. To evaluate disease extent and exclude multisystem involvement, positron emission tomography combined with CT was performed, showing disease confined to the stomach. Given the absence of symptoms and lack of multisystem disease, a surveillance strategy with interval imaging was pursued in collaboration with oncology. Discussion: Adult LCH is rare, with an estimated annual incidence of 1-2 cases per million. Isolated GI involvement is especially uncommon, with only a few cases reported in the literature. Diagnosis requires histopathologic and immunohistochemical confirmation, often supported by molecular testing for BRAF mutations. This case emphasizes the importance of vigilance and comprehensive diagnostic evaluation with sampling of gastric lesions, even when subtle or atypical, and highlights the need for tailored, patient-centered management through a multidisciplinary approach.