Poorly differentiated carcinoma express-

Cytokeratins are proteins of keratin-containing intermediate filaments found in the intracytoplasmic cytoskeleton of epithelial tissue. The term "cytokeratin" began to be used in the late 1970s (for example, see "Intermediate-sized filaments of human endothelial cells" by Franke, Schmid, Osborn and Weber) when the protein subunits of keratin intermediate filaments inside cells were first being identified and characterizedThe subsets of cytokeratins which an epithelial cell expresses depends mainly on the type of epithelium, the moment in the course of terminal differentiation and the stage of development. Thus this specific cytokeratin fingerprint allows the classification of all epithelia upon their cytokeratin expression profile. Fuhermore, this applies also to the malignant counterpas of the epithelia (carcinomas), as the cytokeratin profile tends to remain constant when an epithelium undergoes malignant transformation. The main clinical implication is that the study of the cytokeratin profile by immunohistochemistry techniques is a tool of immense value widely used for tumor diagnosis and characterization in surgical pathology.