NR4A1 and breast cancer: Triple-negative breast cancer (TNBC) is a biologically aggressive form of breast cancer defined by the absence (0 or ≤1% immunohistochemistry (IHC) expression) of the hormone receptors (HR) estrogen (ER) and progesterone (PR), as well as a lack of amplification of the human epidermal growth factor receptor 2 (HER2), accounting for up to 20% of breast cancers [1].