The relation between use of oral contraceptives (OCs) by young women and their risk of breast cancer before 45 years of age was investigated by analysis of data from a population-based, case-control study conducted in eight geographic regions of the United States. 2088 women with breast cancer diagnosed between Dec 1, 1980, and Dec 31, 1982, were compared with 2065 controls selected during the same period. There was no significant increase or decrease in the risk of breast cancer for OC users according to age at first use or subsequent duration of use, even for women who first used OCs before the age of 20 years and who continued to use them for more than 4 years. Risk was not altered significantly for women who used OCs with high progestagen "potency" before the age of 25 years (even when duration of use exceeded 6 years), for those who used OCs before first-term pregnancy (even when duration of use exceeded 4 years), or for OC users according to age at diagnosis. These results suggest that use of OCs by young women in the United States has no effect on the aggregate risk of breast cancer before 45 years of age.
PIP: The relationship between use of oral contraceptives (OC) by young women and their risk of breast cancer before age 45 is analyzed from data obtained from 8 geographical regions in the US. 2088 women with breast cancer were compared with 2065 controls. There was no significant increase or decrease in the risk of breast cancer for OC users according to age at 1st use of OC. The results suggest that the use of oral contraceptives by young women in the US has no effect on the aggregate risk of breast cancer before 45 years of age. The major sources of error in studies of this type are bias in selection of cases compared with controls, bias or general inaccuracy in the information about use of OCs, confounding and chance. It is thought unlikely that any of these sources of error are of importance in relation to the results of this study.