While phenotyping based on gene expression using qPCR was possible for cells from BC cell lines (Fig. S5B), it was not possible to definitively classify CTCs from clinical samples to EMT phenotypes (Fig. S5D); no mRNA expression of mesenchymal marker genes (SERPINE1, PLS3) was detected in CTCs (data not shown), which were used to confirm the phenotypes of BC cell lines (Fig. S5B). Here, PLS3 is linked to breast cancer.