ERBB2 and neoplasm: Hence, it is possible that 10 % of all patients with MBC might benefit from HER2-directed treatment despite their primary tumor being HER2-negative since about 80 % of all patients are PRIM-HER2-negative, half of whom are CTC-positive (≥5 CTCs/7.5 mL blood) in the metastatic setting where the rate of CTC-HER2 positivity (i.e., immunostaining score 3+ or 2+) is about 30 %.