ESR1 and breast cancer: In the current study, we found that the ER+ luminal A-like MCF7 breast cancer cells-derived ER+, estrogen-independent, and Tamoxifen-resistant MCF7-TamC3 cells exhibit increased expression of NUPR1 and molecular/cellular characteristics, which resemble those of the EGF-dependent ERBB2-enriched subtype-like breast cancer cells.