Interestingly, Zhao et al. [21] found a negative correlation between tumor shrinkage upon antiangiogenic therapy and the degree of vascular differentiation (CD31+/CD34– and CD31–/CD34+), suggesting that tumors bearing a higher proportion of undifferentiated vessels (CD31–/CD34+) display a greater susceptibility to bevacizumab. Here, PECAM1 is linked to neoplasm.