In addition, to prevent prostate cancer cells from migrating and invading other tissues, metformin may induce the upregulation of PEDF in prostate cancer cells [14]; metformin also inhibits the mTOR signaling pathway, which mediates the inhibitory effect of dipeptidyl peptidase-4 (DPP-4) inhibitors on breast cancer. This evidence concerns the gene DPP4 and prostate cancer.