ERBB2 and breast cancer: From a biological perspective, our study also shows that most Luminal B or Her2-E tumors with the potential of lowering their proliferative biology will change their intrinsic subtype to Luminal A or normal-like within just 2 weeks of treatment, but more “endocrine-resistant” breast cancer such as basal-like and some Luminal B and Her2-E will not change despite prolonged AI treatment.