PECAM1 and colorectal carcinoma: Analysis of angiogenesis in the CT26, Colo-205, and Co5896 CRC PDX models and the GIST PDX model showed a significant reduction in tumor vessel area or vessel number in regorafenib-treated xenografts, assessed by CD31 staining, while no significant change in microvessel area was observed in the regorafenib-refractory Co8541 CRC model [25, 30, 41, 42].