ERBB2 and breast cancer: One study showed that, while 17 of 23 patients with HER2 3+ (IHC) breast cancer retained HER2 3 + status, 2 and 4 patients showed HER2 2+ (IHC) and 1 + or 0 (IHC), respectively, at the primary site after neoadjuvant trastuzumab-based therapy [34].