CLDN1 and colorectal cancer: Claudin-4 (cldn4) is a member of the claudin gene family that includes the genes claudin-1 (cldn1) and claudin-7 (cldn7) which have been shown to be up-regulated in a variety of tumors and their associated premalignant lesions, including colorectal cancer and cancers of the pancreas and oesophagus [3, 36].