Role of progestogens in the prevention of breast cancer

The incidence of breast cancer has continued to decrease each year at Wilford Hall United States Air Force Medical Center with the ever-increasing use of combined progestogen-oestrogen replacement therapy over the past 12 yr. By 1983, the overall incidence of breast cancer had fallen to 53.9:100 000. The lowest rate for the 9 yr of a prospective study to 1983 was seen among the oestrogen-progestogen users (66.8:100 000) although it was also slightly reduced in both the unopposed oestrogen users (142.3:100 000 and the oestrogen vaginal cream users (116.3:100 000). The incidence was significantly lower in both the oestrogen-progestogen users and the oestrogen users (P less than or equal to 0.01) as compared with untreated women (343.5:100 000). These data further strengthen the growing evidence that the addition of progestogen to oestrogen decreases the risk of mammary malignancy.