Evaluation of long-term outcome data such as 5-year DFS together with correlative biological studies evaluating proliferation markers (e.g., Ki-67) and selected predictive factors of response to neoadjuvant treatment in HER2-positive BC (e.g., EGFR and PTEN) are currently underway in our laboratory to adequately appraise whether those patients who received neoadjuvant metformin might gain an additional survival benefit and the mechanisms involved [35, 40–44]. This evidence concerns the gene EGFR and breast cancer.