Accordingly, we assessed quantitative levels of gene expression for seven transcripts that have been previously associated with the presence of BM DTCs in BC patients [32]—EPCAM, ERBB2, PD-L1, PDGFRB, STEAP1, TWIST1, and WNT5A- by droplet digital PCR (ddPCR) pre- and post-Parsortix enrichment. The gene discussed is ERBB2; the disease is breast cancer.