2002). Mitochondrial respiration defects in cancer cells lead to elevated levels of NADH, which could inactivate PTEN, enhance glycolysis, and increase cell survival (Pelicano et al. 2006). In addition, the mutations of mtDNA in cancers have critical impacts on tumorigenesis and metastasis (Ju et al. 2014). The gene discussed is PTEN; the disease is cancer.