Malignant solitary fibrous tumor of the meninges

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Abstract
Increasing numbers of solitary fibrous tumors (SFTs) in the meninges have been reported since this entity was first recognized. While most cases previously reported were considered to be benign, the malignant potential of extrathoracic SFTs has not been excluded. The authors report a rare case of a meningeal SFT with malignant behavior occurring in a Japanese female patient, initially resected when she was 44 years old and recurring in the same place four times during a 26-year follow-up period. A metastatic tumor to the right lung arose 25 years after the resection of the first meningeal tumor and focal invasion into the cerebellum was also observed with her last (5th) meningeal tumor. Immunohistochemical analysis showed all tumors to be diffusely positive for CD34 and negative for EMA, with a so-called “patternless” histological pattern, featuring thin collagen fibers between tumor cells. A focal “staghorn” vascular pattern was also observed. Ki67 (MIB-1) labeling indices and mitosis rates were 3.1±1.2% and less than 1/10 high power fields (HPF) in the first meningeal tumor and 16.1±6.4% and 6/10HPF in the last (5th) one, respectively. Thus, the present case suggests that meningeal SFTs possess malignant potential so that careful long-term follow up is required.