CTC positivity by gene expression analysis in breast cancer is also assessed by means of RT-PCR for other epithelial markers and breast normal/tumor tissue-associated genes, such as EPCAM, MUC1, SCGB2A2 and ERBB2, whose detection frequencies in non-metastatic compared to advanced disease case series are 0–19% versus 17%, 0–41% versus 10%, 11–14% versus 20–34%, 6–14% versus 10–20%, respectively, per each gene [124,135,155,156,158,159]. The gene discussed is ERBB2; the disease is breast carcinoma.