Triple-negative breast cancer (TNBC) is particularly sensitive to cyclin-dependent kinase 7 inhibitor, THZ1, compared to hormone receptor (HR)+ breast cancer, but our data found that different TNBC cell lines had a wide range of IC50 values of THZ1, suggesting a possible heterogeneity in sensitivity to THZ1 in TNBC. This evidence concerns the gene CDK7 and breast cancer.