ERBB2 and breast carcinoma: When a positive CK5/6 staining in ≥ 10% of the HER2+ breast cancer tissue sections was registered as a diagnostically relevant positive reaction [21], patients with basal 2-HER2+ tumors (but not basal 1-HER2+ tumors) were older (P = 0.034) and more likely to have larger tumors (P = 0.003) and recurrence (P < 0.001) than those with luminal-HER2+ and HER2+ tumors.