Immunohistochemical localization of endothelial cell markers in solitary fibrous tumor

Solitary fibrous tumor (SFT) is an uncommon tumor first reported in the pleura, but recently described in other tissues. CD34, which is expressed in hematopoietic stem cells, endothelial progenitor cells and vascular endothelial cells, is observed in most SFT and some investigators believe that its expression is a definitive marker of this tumor. In the present study, the expression of vascular endothelial cell markers, such as vascular endothelial growth factor receptor (VEGFR)‐1 (flt‐1), VEGFR‐2 (flk‐1/KDR), Tie‐2 and c‐Met, was examined in SFT to clarify the relationship between SFT and endothelial cells. By immunohistochemical staining of tumor cells from 26 patients, VEGFR‐1 was detected in 24 (92%), VEGFR‐2 in five (19%), Tie‐2 in 14 (54%), and c‐Met, a specific receptor of hepatocyte growth factor (HGF) in 23 patients (88%). Furthermore, VEGFR‐3 (flt‐4) immunoreactivity was detected in eight of 26 patients (31%). In contrast, VEGF, VEGF‐C and HGF, which are ligands for the receptors, were not localized in the SFT cells. These findings indicate that most SFT may closely relate to vascular or lymphatic endothelial cells and the endothelial growth factors may contribute to the growth of SFT in a paracrine manner.