We herein investigated whether the presence of the rs11212617 C allele could predict the pathological complete response (pCR) in the METTEN study (23, 24), a randomized, open-label, multicenter, phase 2 trial of neoadjuvant metformin in combination with trastuzumab and chemotherapy in women with early HER2-positive breast cancer. This evidence concerns the gene ERBB2 and breast cancer.