Because claudins 3 and 4 are overexpressed in adeno, squamous and small cell carcinomas [40, [81] [82] [83] they might be susceptible to CPE-mediated treatment. In a recent publication Yao et al created a modified CPE protein containing segments of pseudomonas aeruginosa enterotoxin A [104] . Treatment of cell lines containing claudin 4 induced apoptosis and cell destruction in them [105] . CPE also causes dislocation of claudin 4 from the tight junction in ovarian carcinoma cells and sensitizes them to chemotherapeutic drugs [105] . This effect is achieved by using a modulated C-terminal fragment of the CPE molecule in the treatment which is able to bind to claudin 4 and cause tight junctional loosening but harbours no toxic effects of the N-terminal part of the molecule thus enabling a better influx of chemotherapeutic agents to the cancer tissue (105) . Such CPE mediated treatment could also be one option in treatment of claudin 3 or 4 positive lung cancer.