HER2 expression on DTCs in breast, ovarian and esophageal cancer [67, 282, 308]Gain of HER2 expression in esophageal cancer DTCs confers high risk of early death [67]HER2 expression on breast cancer DTCs as a prognostic marker for OS and PFS [309–311]52% concordance of HER2 expression on primary tumor and DTCs in patients with early breast cancer [312]. The gene discussed is ERBB2; the disease is breast carcinoma.