The versatility of cytokeratins as tumor markers

Cytokeratins are particularly versatile tools in tumor biology both experimentally and clinically. Previously regarded as a rigid intracellular skeleton, the cytokeratins are now known to provide a more dynamic structural integrity within epithelial cells. This more flexible nature of cytokeratin function occurs through rapid shifts in assembly/disassembly states, geared by phosphorylations/dephosphorylations in the 'head' and 'tail' regions of the monomeric filaments. When released from proliferating or dying tumor cells, they provide a useful marker for epithelial malignancies, as evidenced by the number of available immunochemical assays for cytokeratins. Another significant area of interest that highlights their utility is the deposition of cytokeratins in the necrotic areas of tumors, providing an effective target for radioimmunotherapy and radioimmunolocalization. Moreover, the appearence of cytokeratin neodeterminants seems to be a very early event during apoptosis. Indeed, the involvement of specific cytokeratin degradation patterns resulting from the activity of caspases during apoptosis highlights yet another developing field of research devoted to these highly pleomorphic and complex structures.