In fact, in the METTEN phase II trial involving 79 individuals affected by HER2-positive BC bearing the rs11212617 C allele, metformin combined with neoadjuvant chemotherapy (anthracycline/taxane-based regimens) and ERBB2-targeted therapy (i.e., trastuzumab) was associated with a higher pathological complete response (pCR) compared to the non-metformin counterparts (81.2% vs. 35.3%, respectively) [146]. This evidence concerns the gene ERBB2 and breast cancer.