In a study of 254 patients with metastatic breast cancer, 33% of patients with HER2-negative (HER2-) primary tumors had HER2+ CTCs [39], suggesting that CTCs could be used to identify patients with disease sensitive to HER2-targeted therapies regardless of primary tumor HER2 expression and could be used to construct personalized treatment strategies. Here, ERBB2 is linked to neoplasm.