Cytokeratin 19

Cytokeratin 19 (CK19) is a low molecular weight acidic keratin mainly present in simple and stratified epithelium. It has various functions such as maintaining morphology, regulating proliferation, and forming barrier. In clinical practice, CK19 has become a diagnostic indicator of glandular epithelial tumors such as lung cancer, gastric cancer, colorectal cancer, prostate cancer, breast cancer, etc. For example, the positive rate of CK19 in papillary thyroid carcinoma is significantly higher than other benign and malignant lesions, which makes it useful for assisting in identification. Moreover, the characteristic that CK19 is lowly expressed in normal lymph nodes but abnormally up-regulated after lymph node metastasis makes it become an ideal biomarker for tumor micrometastases. In addition, some research found the CK19 positive hepatocellular carcinoma, which has higher invasiveness compared to being negative, speculated that the self-renewal and rapid proliferation ability of CK19+ liver progenitor cells is stimulated when the cells deteriorate. But CK19 is believed to be down-regulated with the increased clinical risk of prostate cancer.