Case Report: Malignant solitary fibrous tumor of the greater omentum

Abstract

Solitary fibrous tumor (SFT) is a rare mesenchymal neoplasm that can occur in almost any anatomic site. Malignant SFT originating from the greater omentum is extremely rare. The Demicco risk-stratification system is commonly used to estimate postoperative recurrence and metastasis risk in patients with SFT. We report a case of malignant SFT derived from the greater omentum and summarize its clinical manifestations, imaging features, immunohistochemical profile, diagnostic criteria and treatment strategy to improve clinicians’ recognition of this rare abdominal tumor. A 37-year-old man presenting with an incidental, asymptomatic left abdominal mass underwent abdominal contrast-enhanced computed tomography (CT) for preoperative evaluation. CT revealed a 9.3×7.9 cm lobulated hypervascular omental mass, accompanied by a tiny suspicious low-density nodule in liver segment III. Comprehensive serum tumor markers were within normal limits. Complete R0 (microscopically margin-negative) radical resection via open laparotomy was performed. Intraoperative en bloc resection of the tumor and partial greater omentum was accomplished without perioperative complications. Postoperative hematoxylin-eosin staining and immunohistochemical examination were conducted to confirm the pathological diagnosis. Postoperative histopathology showed atypical spindle cells, mitotic activity ≥4 per 10 high-power fields, and tumor necrosis ≥10%. Immunohistochemistry showed diffuse positivity for cluster of differentiation 34 (CD34), nuclear signal transducer and activator of transcription 6 (STAT6) and cluster of differentiation 99 (CD99), while S100, cytokeratin, epithelial membrane antigen, CD117 and DOG1 were negative, excluding gastrointestinal stromal tumor and other spindle cell malignancies. The 2017 modified Demicco risk scoring system was applied for prognostic stratification. The patient scored 5 points and was classified as intermediate risk. Regular enhanced CT surveillance was arranged. Twelve-month follow-up imaging demonstrated no local recurrence, and the hepatic nodule remained stable. Malignant behavior may occur across a broad range of patient ages and tumor sizes in primary omental SFT. Diffuse and strong nuclear STAT6 immunoreactivity serves as the highly reliable primary diagnostic hallmark. Radical R0 surgical resection remains the core curative treatment. The 2017 modified Demicco risk scoring system effectively guides postoperative management, and intermediate-risk patients require continuous, long-term imaging surveillance.