EGFR and breast cancer: While CTC isolation was based on cell density and EpCAM protein expression on the surface, the molecular characterization included a multimarker quantitative PCR (qPCR), targeting stem cell markers (CD24, CD44, ALDH1), the epithelial marker CK-19, the mesenchymal marker TWIST and BC-specific markers (ESR1, PR, HER2, EGFR).