ESR1 and breast cancer: Thus, upregulation of NUPR1 might promote the induction of endocrine therapy resistance (estrogen independence and Tamoxifen resistance) in ER+ breast cancer cells through modulations on multiple cell surface receptor-related/unrelated signaling pathways and molecules like BIRC5 and ERBB2, shifting the cellular properties towards other breast cancer subtypes like ERBB2 (HER2)-enriched breast cancer.