Claudins are tight junction proteins that are
critical for the sealing of cellular sheets and controlling
paracellular ion flux. The claudin family of proteins is
composed of at least 24 closely related transmembrane
proteins, most of them are well characterized at the gene
and protein levels. The claudins are present in variety of
normal tissues, hyperplastic conditions, benign
neoplasms, and cancers that exhibit epithelial
differentiation. Loss of claudins expression has also been
reported in several malignancies as well. Differential
expression of various members of the claudins family in
cancers can be used in confirming the histologic identity
of certain cancers and excluding others. Examples
include the use of immunohistochemical detection of
claudins to differentiate between oncocytoma and
chromophobe renal cell carcinoma, endometrial
endometrioid carcinoma and seropapillary carcinoma,
mesothelioma and metastatic adenocarcinoma,
hepatocellular and biliary tract carcinomas, and between
intestinal-type and diffuse-type gastric carcinoma.
Expression of certain claudins can also be used as
markers that can predict patient’s prognosis. Thus, it
seems that attempts to identify expression claudins in
cancers are becoming increasingly useful in histologic
diagnosis of tumors as well as means to assess patient’s
prognosis