ESR1 and breast cancer: Having validated the generation of SASP through this experimental set‐up, control (CTL, from MRC‐5/RAF:ER untreated with 4‐OHT) and SASP conditioned media were added to several breast cancer cell lines with molecular features representative of breast cancer cells: MCF‐7 (ER+; WT p53), T47D (ER+; mutated p53), or MDA‐MB231 (ER‐; mutated p53).