pCR has been proven to be a good prognostic marker to predict long-term survival in breast cancer [7,89]; therefore, it is considered a suitable surrogate end point for patients with luminal B/HER2 negative, HER2 positive (non-luminal), and TN disease but not for those with luminal B/HER2 positive or luminal A tumors [86,90]. This evidence concerns the gene ERBB2 and breast cancer.