Low-Grade Gastric Fibromyxoid Sarcoma in an Adult Female: A Rare Case Report

Abstract Low-grade fibromyxoid sarcoma (LGFMS) is an uncommon soft tissue tumor that often masquerades as benign due to its deceptively mild histopathological appearance. Predominantly arising from the deep soft tissues of the extremities and trunk, LGFMS is exceptionally uncommon in the gastrointestinal (GI) tract. While most documented cases have been found in the small intestine and colon, only one prior case has been reported in the stomach involving an elderly Japanese woman. In this report, we present a compelling case of gastric LGFMS in a 21-year-old female who experienced mild hematemesis and fatigue. An abdominal computed tomography scan unveiled an ill-defined, hypodense mass originating from the lesser curvature of the stomach and extending toward the left hepatic lobe—highlighting the complexity of this condition. Further investigation included an upper endoscopy and an incomplete laparoscopic resection of the tumor. Histopathological analysis revealed a proliferation of spindle cells with focal whorling within a heavily collagenized stroma, transitioning abruptly to a myxoid area, thus confirming a diagnosis of LGFMS. Immunohistochemical testing showed positive results for vimentin and BCL2. Crucially, molecular analysis identified the FUS-CREB3L1 fusion. Based on our search in the literature review, this case is considered a second instance reported in English literature.