In our recent study, we detected increased levels of the vascular endothelial growth factor/vascular permeability factor (VEGF), a potent cytokine and key regulator of physiological and pathological angiogenesis, in the ascites and serum of ovarian cancer patients associated with a simultaneous decreased amount of the tight junction protein claudin 5 in the peritoneal vessels [9]. Here, CLDN5 is linked to ovarian cancer.