Cytokeratin 19 (CK19) as a marker for Epithelial Differentiation and Malignant Transformation: Its Clinical relevance in Diagnosis, Prognosis and Treatment response monitoring

Cytokeratin 19 (CK19) is a type I cytokeratin found mostly in epithelial tissues with high plasticity such as stem cells, transforming cells or tumorous cells. CK19 increases its expression level during epithelial embryogenesis, tissues regeneration, tissue repair as well as tissue development and has shown to have an increasing expression in carcinogenesis of CK19-positive cancers from normal tissues to premalignant lesions to carcinoma in situ. The insertion of CK19 in CK19-negative carcinoma cells induced the metastatic progression characterized by angiogenesis, invasion to surrounding tissues, increased proliferation and drug resistance. Hence, the detection of intracellular CK19 protein by immunohistochemistry (IHC), CK19 transcripts by quantitative Real time RT-PCR or One-step nucleic acid amplification (OSNA) and serum CK19 fragments such as Cyfra 21-1 by enzyme-linked immunosorbent assay (ELISA) could help in diagnosis to confirm the presence of the cancerous cells, in prognosis to predict the course the cancer is mostly likely to take and in treatment response monitoring to investigate the effectiveness of the treatment so that the early adjuvant therapy could be used in case the treatment was found ineffective during the follow-up studies.