ESR1 and breast cancer: The cell panel included nine breast cancer cell lines (MCF‐7, T47D, HCC1954, JIMT‐1, MDA‐MB‐436, MDA‐MB‐231, MDA‐MB‐468, HCC1937 and Hs578T) representative of the ER+/PR+, HER2+ and TNBC molecular subtypes.