HER2 expression on CTC of metastatic breast, non-small cell lung, gastric, gastrointestinal, ovarian cancer [12, 13, 36, 119, 178, 189, 282]Anti-HER2 therapy to address HER2-positive CTCs [283]HER2 is part of the signature of breast cancer CTCs competent for brain metastases [284]. The gene discussed is ERBB2; the disease is breast carcinoma.