Keratin 18 (KRT18) - Epithelial cell marker used for differential diagnostics of cancer

The keratin gene family is a large group of intermediate filament and structural proteins that provide the structural components of hair, nails, horns, scales, claws and similar types of hard tissues. Keratins are also important for intracellular stability in epithelial tissues and different keratins often display organ- or tissue specific expression patterns. Due to these specific expression patterns, keratins are often used as diagnostic biomarkers. Keratin 18 is a type I keratin and expressed in simple epithelia including glandular cell types present in the GI-tract, female tissues, male tissues, and respiratory epithelium. Clinically, keratin 18 is used together with keratin 19 to distinguish hepatocellular cancer from cholangiocellular carcinoma (both keratins are expressed in bile ducts, but keratin 18 is expressed in hepatocytes whereas keratin 19 is not).