CDK8 and breast cancer: Research has shown that CDK8 enhances the estrogen receptor (ER) in breast cancer by stimulating Ser2 phosphorylation of estrogen-induced RNA pol II CTD, thus more effectively assisting in the transcription process of ER-inducible genes, such as GREB1、CXCL12 and TFF1 (Figure 1A) (McDermott et al., 2017).