NR4A1 and breast cancer: The reasons for the difference in the expression of hormone receptor may be as follows: (1) the proportion of premenopausal and postmenopausal women with breast cancer in China is opposite of that in foreign countries 15; (2) the stimulation of different human populations and the external environment affect the expression of hormone receptor; and (3) pregnancy and childbirth lead to the fluctuation of estrogen and progesterone levels, which affect the expression of hormone receptor.