To evaluate the preclinical efficacy of RMC-6272 in breast cancer, we tested its effects on cell proliferation and survival in a panel of 20 different breast cancer cell lines spanning the three distinct molecular subtypes: ER+/HER2−, HER2+, and triple-negative breast cancer (TNBC) (Supplementary Table 1). This evidence concerns the gene ESR1 and breast carcinoma.