Abstract 3007: Heterogeneity of vascular endothelial growth factor receptors 1, 2, and 3 in primary human colorectal adenocarcinoma

The Vascular Endothelial Growth Factor (VEGF) pathway plays an important role in the genesis, growth and progression of human cancer, including colorectal carcinomas (CRC). The key mediators of VEGF signaling are VEGFR1, VEGFR2, and VEGFR3, part of a family of related receptor tyrosine kinases. The relative expression, activity, or interplay among these receptors may determine the response of CRC patients to anti-angiogenic therapies. Using high-affinity, specific monoclonal primary anti-VEGFR1, 2 3 antibodies, we have developed robust imunohistochemical assays in our laboratory to quantify VEGFR1, 2 and 3 in archival human tissues. Using a well-annotated CRC tissue microarray (TMA), we carried out comprehensive comparative evaluation of immunohistochemical (IHC) expression of the three VEGFRs in archival primary CRC tissues (n=84). VEGFR1 immunoreactivity was reported as H-score (range 0-300); VEGFR2 positive vessels were counted and normalized to the number of CD34-positive vessels and reported as vascular positivity index (VEGFR2-VPI) and VEGFR3-positive vessels were counted in each core by the same solid tumor immunopathologist, who was blinded to the clinico-pathologic details. Based on immunoreactivity for VEGFRs, each case was scored as negative, low, medium or high. Thresholds were selected based on the overall range of expression of each receptor in the CRC tissues examined: 0, 1-50, 51-100, >100 (VEGFR1 H-scores); 0, 1-25, 26-49, 50-100 (VEGFR2-VPI); 0, 1-5, 6-10, >10 (VEGFR3+ vascular count). Based on VEGFR (1,2,3) expression, a set of eight VEGFR staining profiles were noted: Triple VEGFR positive (n=9, 11%), VEGFR1 predominant (17, 20%), VEGFR2 predominant (7, 8%), VEGFR3 predominant (1, 1%), VEGFR1/2 predominant (42, 50%), VEGFR1/3 predominant (2, 2%), VEGFR2/3 predominant (3, 4%), and triple VEGFR negative (3, 4%). These new data provide original insights on the distribution, subcellular localization and heterogeneity of expression of VEGFRs in human CRC stromal vessels and tumor cells. The proposed human CRC sub-classification, based on the observed differential VEGFR 1, 2, 3 expression profiles, has identified various subsets of human CRCs. Clinical trials incorporating IHC profiling would be required to test whether these subsets show differential responsiveness to targeted agents in the VEGF/VEGFR2 family. Citation Format: Timothy R. Holzer, Leslie A. O'Neill, Drew M. Nedderman, Angie D. Fulford, Beverly L. Falcon, Mark T. Uhlik, Laura E