As an alternative approach,isoform-selective CDK inhibitors have potential to be safer and moreeffective, as evidenced by CDK4/6 inhibitors such as abemaciclib,palbociclib, and ribociclib in the treatment of estrogen receptor-positive/humanepidermal growth factor receptor 2-negative (ER+/HER2−) metastaticbreast cancer.5,6 Despite these successes with CDKinhibition as targeted cancer therapy, there remains significant unmetneed in other tumor types with evident transcriptional deregulation,such as triple-negative breast cancer (TNBC), which is highly MYCdependent.7,8. This evidence concerns the gene ESR1 and neoplasm.