Abstract: In cancers such as prostate cancer, the combination of PTEN loss and activation of Myc activates an adaptive stress response that enables tumor cells to escape the stress of massively upregulated protein synthesis. This pro-survival response is mediated by the PERK-phosphorylated eIF2? axis of the UPR adaptive response. Agents that disrupt PERK-eIF2? pathways disrupt the adaptive response and lead to cancer cell death from uncontrolled growth. For example, ISRIB and derivatives may be employed as therapeutic agents to disrupt PERK-mediated adaptive mechanisms. Additionally PTEN loss and activation of Myc provides a diagnostic marker that enables better prognosis and the selection of amenable treatments.