ESR1 and breast cancer: Of note, no consistent and strong alterations of luminal and basal gene sets enrichment levels were detected in ESR1 WT endocrine resistant ER+ breast cancer cell models21,40–47 (eight tamoxifen resistant, two fulvestrant resistant, and seven long-term estradiol deprivation (LTED) models), suggesting that the “basal-ness” shift is a unique feature acquired as a result of ESR1 mutations (Supplementary Fig. 3e).