Solitary Fibrous Tumor of the Stomach: Diagnostic Pitfalls and Clinical Implications.

Introduction: Solitary fibrous tumor (SFT) is a rare mesenchymal neoplasm that most commonly originates in the pleura but can also occur at extrapleural sites, including the abdominal cavity. Among these, primary SFT of the stomach is exceptionally rare. Due to overlapping clinical, endoscopic, and radiologic characteristics, distinguishing SFT from gastrointestinal stromal tumor (GIST) can be particularly challenging. Misdiagnosis may result in inappropriate treatment, such as unnecessary administration of imatinib. Therefore, accurate preoperative differentiation is essential for appropriate management.

Case presentation: A 74-year-old man was incidentally found to have a submucosal gastric tumor during a routine health checkup and was referred to our hospital for further evaluation and treatment. Upper gastrointestinal endoscopy revealed a 30-mm subepithelial lesion on the greater curvature of the gastric fundus. Endoscopic ultrasound-guided fine-needle aspiration (EUS-FNA) demonstrated isolated and clustered cells with ovoid to spindle-shaped nuclei. Although not definitive, the combined endoscopic and cytological findings led to a preoperative diagnosis of suspected GIST, and laparoscopy and endoscopy cooperative surgery (LECS) was subsequently performed for local resection. Histopathological examination of the resected specimen revealed an irregular proliferation of spindle cells and nuclear immunopositivity for signal transducer and activator of transcription 6 (STAT6), leading to a final diagnosis of SFT of the stomach. According to Demicco's risk stratification model, the tumor was classified as low risk. The patient underwent complete resection via LECS and has remained free of recurrence for more than 2.5 years postoperatively.

Conclusions: This case highlights the difficulty in differentiating SFT from GIST preoperatively and underscores the importance of obtaining sufficient tissue samples to allow for immunohistochemical analysis, particularly STAT6 staining. Recognizing gastric SFT as part of the differential diagnosis is critical to avoid misdiagnosis and ensure appropriate therapeutic decision-making.