Our results demonstrate that the effects of acute Opa1 deletion are mediated by unopposed mitochondrial fission; however, that simultaneous Drp1 deletion rescues colony formation, ETC assembly and function, and cristae morphology in vitro, but not tumor development in vivo, suggests that additional unidentified factors influence the sensitivity of in vivo tumor development to mitochondrial dynamics disruption. This evidence concerns the gene OPA1 and neoplasm.