ESR1 and breast cancer: Indeed, CDK8 knockdown or CDK8/19 inhibition in colon cancer selectively suppressed the growth of metastatic but not primary tumors [6], suppressed invasive growth by counteracting epithelial-mesenchymal transition [7], interfered with damage-induced secretion of proteins enhancing tumor growth and drug resistance [8], primarily through an effect on NFκB-induced transcription [5], and suppressed the development of resistance to estrogen deprivation in estrogen-receptor positive breast cancers [9].