One phase II trial using metformin in breast cancer patients receiving DOX has previously been started but was terminated due to insufficient accrual of patients.1 Future clinical trials are warranted to assess the potential cardioprotective effect of metformin in DOX-treated cancer patients, though careful consideration of dose and treatment scheme have to be made to ensure maximal cardioprotective potential through AMPK activation without severe adverse effects. This evidence concerns the gene PRKAA1 and breast cancer.