PECAM1 and neoplasm: Although NRP1 is a known co-receptor for VEGF, no differences were observed in intra-tumoral vascularization between the treatment groups as measured by CD31 immunohistochemistry, suggesting that the tumor suppressive effects of Vesencumab were not primarily mediated by changes in tumor angiogenesis, but direct effects on tumor cells expressing NRP1 (Fig. 5g and Hii).