The METTEN trial (EudraCT number 2011-000490-30) was a randomized multicenter phase II trial to evaluate the efficacy, tolerability, and safety of neoadjuvant chemotherapy and trastuzumab in combination with metformin or placebo for 24 weeks in nondiabetic patients with early-stage HER2-positive breast cancer. Here, ERBB2 is linked to breast carcinoma.