CDK8 and breast cancer: CDK8 is upregulated in breast cancers, associated with tumor progression and high expression of CDK8 predicts shorter relapse-free survival of breast cancer patients.369 In breast cancer Xu and colleagues identified CDK8 as a key regulator of G2/M transition, polyploidy, cell migration, and proliferation through the control of the ubiquitin ligase Skp2 and histone variant macroH2A1 (mH2A1) axis.