PECAM1 and neoplasm: Furthermore, CD31/Ki67 double staining of corresponding tumor sections (Fig. 4c, d right panels) revealed a significant reduction in the percentage of proliferating endothelial cells in vessels that were subjected to systemic GEM treatment (GEM: 22.3 ± 4.2%, vehicle: 30.9 ± 3.9%, p = 0.002, Fig. 4g).