NR4A1 and breast cancer: In vitro culture studies demonstrated that the small molecule N-allyl noroxymorphone reduced human breast tumor cell number in a dose-dependent manner 72-hours after administration for both the BT474 breast cancer cells (hormone receptor positive (HR+)/ HER2+) and the HR-positive/ HER2-negative MCF7 breast cancer cells when compared to the HUMEC primary breast epithelial cells (Fig 5).