Decoding a Soft Tissue Enigma: Malignant Solitary Fibrous Tumour of Thigh

Abstract

Solitary fibrous tumour (SFT) is a rare mesenchymal neoplasm, most commonly arising from the pleura, with infrequent extra-pleural involvement. We report a malignant extra-pleural SFT in a 64-year-old woman presenting with a longstanding thigh mass. Wide local excision demonstrated a spindle cell neoplasm with hemangiopericytoma-like vasculature, necrosis and high mitotic activity. Differential diagnoses included malignant SFT and synovial sarcoma. Immunohistochemistry revealed diffuse CD34 expression and strong nuclear STAT6 positivity, confirming malignant SFT. This case illustrates the diagnostic challenges of spindle cell tumours and emphasizes the importance of STAT6 staining. Owing to malignant potential of extra-pleural SFTs, long-term surveillance is recommended.