However, in breast cancer and other cancers a subpopulation of CTCs with low or absent EpCAM expression exists, which may be a consequence of processes leading to a phenotypic plasticity such as the epithelial-to-mesenchymal transition [8]—a highly conserved mechanism which is associated with cell migration, invasion and dissemination in the development of cancer metastasis [9]. The gene discussed is EPCAM; the disease is breast carcinoma.