CLDN4 and ovarian cancer: Another study showed that the expression of claudin-3 and claudin-4, which are CPE receptors, is significantly higher in chemotherapy-resistant/recurrent ovarian tumors than in chemotherapy-naive ovarian cancers, and that targeting these proteins by CPE-mediated therapy may be effective in killing chemoresistant/recurrent ovarian tumors in vitro and in vivo [132].