Vascular endothelial growth factor receptor 2 (VEGFR2) expression in squamous cell carcinomas of the head and neck

Objectives: Vascular endothelial growth factor receptor 2 (VEGFR2; Flk-1 [fetal liver kinasel/KDR [kinase insert domain containing receptor]) has been identified as a high affinity receptor for vascular endothelial growth factor (VEGF) on vascular endothelium. Head and neck squamous cell carcinomas (HNSCC) have already been shown to produce substantial amounts of VEGF. VEGFR2 is supposed to play a major role in tumor-neoangiogenesis. Methods: We investigated 24 tumor specimens and 4 HNSCC cultured tumor cell lines for the incidence and distribution of VEGFR2 by immunohistochemistry using monoclonal antibodies (mAbs) and RT-PCR. Results: Analysis of frozen sections by immunohistochemistry showed that in 90% of tumor specimens VEGFR2-positive cells were found which were associated with vascular endothelium. VEGFR2 was also expressed on tumor cells and vessels, which was confirmed by double immunolabeling of tumor cells with an a-cytokeratin mAb. Furthermore, 2 (JPPA, SCC9) of 4 HNSCC cultured tumor cell lines revealed positive VEGFR2 immunoreactivity. Synthesis of VEGFR2 mRNA on all 4 HNSCC cultured tumor cell lines (JPPA, SCC9, SCC25, and LFFR) and in 6 tumor specimens was confirmed by RT-PCR. In conclusion, our results showed that VEGFR2 is expressed in HNSCCs on tumor cells. VEGFR2 expression is associated with the beginning of vasculogenesis represented by accumulation of VEGFR2-positive cells budding into new vessels ("hot spots"). The focal expression pattern of VEGFR2 on tumor cells suggests an autocrine loop for VEGF in tumor cell growth.