ESR1 and breast cancer: In extending these studies, we silenced MED1 (Fig. 3f, left panel) and found (i) downregulation of ER, and ER target gene expression (Fig. 3f, right 4 panels) and (ii) inhibition of clonogenic survival (Fig. 3g), indicating that, in addition to SRC-3, MUC1-C regulates the CDK7 → MED1 pathway in HR+/HER2− BC cells.