We also found that two ER+/HER2− lines (MCF7 and T47D) and BT‐474 cells (ER−/HER2+) show a small population of ∆Np63/p40+ cells, suggesting that these may be useful models to investigate the role of ΔNp63/p40 in these breast cancer subtypes. The gene discussed is ESR1; the disease is breast cancer.