Several claudin family members have been shown to be overexpressed in HGSC compared to mesothelioma in gene expression array analysis [6], and several studies have reported on the overexpression of for claudins 1, 3, 4, 5 and 7 proteins in adenocarcinomas of various origin compared to mesothelioma and/or reactive mesothelial cells (RMC) in effusions [7–12]. Here, CLDN1 is linked to mesothelioma.