Although breast cancer is known to be more aggressive and to be associated with a poorer prognosis in premenopausal women than in postmenopausal women, endocrine treatment (ET) is recommended as a standard of treatment by clinical guidelines for hormone receptor (HR)-positive, HER2-negative metastatic breast cancer (MBC) in premenopausal patients [1]. Here, NR4A1 is linked to breast cancer.