CYCS and cancer: It was recently shown that cancer cells which survive brief treatment with cytotoxic concentrations of BH3 mimetics induce MOMP and cytochrome c release which activates the ISR including ATF4 and its target gene ATF3.13 We did not observe ISR activation or ATF4-mediated ATF3 expression in targeted therapy treated persister cells which exhibit lower MOMP and cytochrome c release compared to cells which survive brief cytotoxic BH3 mimetic treatment.