NR4A1 and breast cancer: Breast cancer is categorized into three major subtypes based on the presence or absence of molecular biomarkers, namely estrogen or progesterone receptors and human epidermal growth factor 2 (ERBB2, formerly HER2): hormone-receptor-positive/ERBB2-negative (70% of patients), ERBB2-positive (15–20%) and triple-negative (TNBC, tumors lack the above standard molecular markers, 5%) [1].