PPARGC1A and cancer: The significant contribution of OXPHOS in cancer stemness has notably been proven from the high level of mitochondria biogenesis driven by PPAR-γ co-activator 1a (PGC-1a) in stem-like cancer cells [40], the up-regulation of enzymes involved in the respiratory chain in ovarian CSC [68], and the OXPHOS-dependency of CSC in small cell lung cancer [87,88].