NR4A1 and breast cancer: Breast cancer can be classified according to the receptor expression in the breast cancer cells: hormone receptor-positive, which involves expression of estrogen (ER) or progesterone receptors (PR); human epidermal growth factor receptor 2 (HER2)-positive, which represents over-expression of human epidermal growth factor receptor-2; and the triple negative breast cancer that is negative for ER, PR, and HER2 receptors [4,25].