CDK8 and cancer: Even though CDK inhibitors have been abundantly described, attempts of discovering selective CDK8 inhibitors have emerged as a promising strategy for cancer therapy as Pan-CDK inhibitor has shown narrow therapeutic window and potential risks (Al-Sanea et al., 2015a; Al-Sanea et al., 2015b; Al-Sanea et al., 2016b; Firestein et al., 2008; Kapoor et al., 2010; Xu & Ji, 2011).