Protein Markers Used in CTC Investigations
EpCAM, also known as HEA or BerEP4, is commonly expressed by many epithelial cells but not in blood cells, adult squamous epithelium, hepatocytes, myoepithelia and mesothelia cells or fibroblasts.[17–19] It has been reported that up to 95% of epithelial tumors express this antigen but is usually not expressed in hepatocellular carcinoma, squamous carcinoma of the skin or mesotheliomas.[20–22] EpCAM is one of the most commonly used markers for the positive isolation and detection of CTCs from patient blood. It is used for CTC isolation in CellSearch®, CTC-Chip and immunomagnetic beads such as MACS® and Dynabeads® (discussed below). However, not all tumors, including those from epithelial or non-epithelial origin, express EpCAM, such as renal cell carcinoma and melanoma. Its expression level also varies across different cancer types which express this marker. Another limitation of using this marker is that the occurrence of epithelial-mesenchymal transition (EMT) in tumor cells lead to downregulation of epithelial markers including EpCAM and reduces the sensitivity for detection of CTC.[23,24]
Expert Rev Proteomics. 2013;10(6):579-589. © 2013 Expert Reviews Ltd.