Menopausal estrogen use and the risk of breast cancer.

The relationship between the occurrence of female breast cancer and menopausal estrogen replacement was investigated in a population-based case-control study. One hundred and eighty-three white female residents of King County, Washington (ages 50-74) in whom breast cancer was diagnosed from July, 1977, through August, 1978, were interviewed with respect to reproductive and other factors, with emphasis on the use of estrogen-containing medication. For purposes of comparison, the same data were collected from 531 white female King County residents of the same ages without breast cancer. Use of menopausal estrogens was reported somewhat more commonly among controls than among cases (relative risk = 0.74, 95% confidence interval = 0.51-1.08) and some variation in proportions of users was present between different hysterectomy-oophorectomy subgroups. However, each of these differences could easily have been due to chance. No substantial trends in risk were apparent with increasing duration of use, time since first use, time since last use, or average dose. The findings suggest that in King County no important relationship exists between use of menopausal estrogens and the occurrence of breast cancer.