Overall, our findings suggest that ovarian cancer cells produce VEGF in order to first induce angiogenesis to allow tumor growth and second increase endothelial permeability via suppression of VE-cadherin and subsequent claudin 5 in the peritoneal vasculature, which finally induces ascites and thereby facilitates dissemination of cancer cells in the abdominal cavity. Here, CLDN5 is linked to ovarian cancer.