CDK7 and breast cancer: CDK7 inhibition can limit these malignant features, as observed in patient-derived xenografts (PDXs) of TNBC.341,356 CDK7 expression is also increased in human epidermal growth factor receptor 2 (HER2) breast cancers, where it might act as a transcriptional cofactor, inducing dysregulated gene expression favoring resistance to HER2 inhibition.