MTOR and neoplasm: In addition, metformin and phenformin trigger the activation of AMP-activated protein kinase (AMPK) that in turn antagonizes the activity of pro-tumor mammalian target of rapamycin (mTOR) signaling, leading to delayed tumor growth and reduced metastasis (Lin et al., 2015; Orecchioni et al., 2015; Navarro et al., 2016).