Expression and localization of basic fibroblast growth factor and its mRNA in solitary fibrous tumor

Solitary fibrous tumors (SFTs) represent a distinct neoplasm that should be included in the differential diagnosis of spindle-cell neoplasms of the soft tissue. Basic fibroblast growth factor (bFGF or FGF-2) is a mitogenic and angiogenic polypeptide produced by diverse cell types, including the cells derived from normal tissue and neoplastic lesions. In this study, the expression of bFGF, vimentin, CD 34, c-kit (or CD 117), desmin, S-100 protein, and alpha-smooth muscle actin (alpha-SMA) in SFTs, hemangiopericytomas (HPC), gastrointestinal stromal tumors (GIST), and dermatofibrosarcoma protuberans (DFSP) were evaluated to assess their usefulness in the differential diagnosis of these lesions. The expression of bFGF mRNA was also examined in SFTs by in situ hybridization (ISH) using a digoxigenin-labeled bFGF oligonucleotide probe. All the SFTs, GISTs and DFSPs exhibited strong and diffuse immunoreactivity for CD34 and vimentin, and were completely negative for desmin, S-100 protein and alpha-SMA. The HPCs were positive for vimentin, but negative for CD34. In all the SFTs, strong and diffuse nuclear immunostaining was observed with bFGF antibody, contrasting with the negative staining observed in the majority of the HPCs, GISTs, and DFSPs. The bFGF mRNA was also expressed in the SFT cells. The constitutive expression of the bFGF in the SFT widens the spectrum of available markers for these tumors, providing a useful addition to their differential diagnosis in difficult cases, and contributing to the understanding of their histogenesis and molecular pathogenesis.