FGFR1 and neoplasm: FGFR1 was found to be predominantly expressed by endothelial cells in the tissue underlying the dysplastic and invasive epithelium (Figure 4E), supporting the proposition that down-regulation of FGF-2 in response to treatment with imatinib is serving to inhibit angiogenesis driven in part by FGFR1 signaling in tumor endothelial cells.