1EPIDEMIOLOGY OF BREAST CANCER IN KOREA

There is overwhelming evidence that ovarian hormones play a crucial role at all stages in the development of breast cancer, and many clinically evident breast cancers remain sensitive to ovarian hormones. Both major ovarian hormones, estradiol and progesterone, play important roles in increasing breast cancer risk. 1) Key epidemiologic evidence The key epidemiologic observations on the relation of ovarian hormones to breast cancer risk are as follows. (1) Early menopause, whether it occurs naturally or through bilateral oophorectomy, reduces risk. (2) Postmenopausal obesity increases risk, but premenopausal obesity decreases risk. (3) Menopausal estrogen replacement therapy increases risk, but only to a relatively small extent. (4) Use of combination type oral contraceptives does not decrease the risk. (5) Use of depot medroxy rogesterone acetate does not decrease breast cancer risk (Pike et al. 1993). 2) Estrogen-augmented-by-progesterone hypothesis The key epidemiologic hormonal risk factors for breast cancer are all explicable in terms of the estrogen augmented by progesterone hypothesis. Early menopause reduces the ris