Basic FGF and Ki-67 proteins useful for immunohistological diagnostic evaluations in malignant solitary fibrous tumor

Solitary fibrous tumor (SFT) is an uncommon soft tissue tumor initially reported in the pleura but recently described in other sites in the body. Morphological distinction between benign and malignant SFT is often difficult. An immunohistochemical study was performed in pleural and extrapleural sites. The aim of this study was to determine if an immunohistochemical method is helpful in distinguishing benign SFT from malignant SFT, and providing valid information to predict the prognosis associated with malignant SFT. Twenty-four cases of benign (14 patients) and malignant (10 patients) SFT in the pleura, pelvic space, prostate and other sites of soft tissue were analyzed. Tumors from 10 patients were diagnosed as malignant on the basis of markedly increased cellularity, mitotic activity (>4/10 high-power fields), nuclear pleomorphism and areas of necrosis. Immunohistochemically, we found a mean basic fibroblast growth factor (bFGF) labeling index of 48.67% (48.67 +/- 8.52%) for benign SFT and 74.5% (74.5 +/- 6.92%) for malignant SFT (P < 0.05). We also found a mean Ki-67 labeling index of 1.9% (1.9 +/- 0.43%) for benign SFT and 6.11% (6.11 +/- 1.05%) for malignant SFT (P < 0.05). Our results suggest that bFGF and Ki-67 are diagnostically relevant to the evaluation of malignant SFT and these proteins are thought to be potentially useful markers for prognosis of SFT.