Contraception and breast cancer.

Oral contraceptive use is weakly associated with breast cancer risk in the general population, but the association among women with a familial predisposition to breast cancer is less clear. Recent studies indicating that oral contraception may increase the risk of breast cancer more in subjects who are BRCA 1 or BRCA 2 mutation carriers. Features of hormonal contraceptive use, such as duration of use, age at first use, and the dose and type of hormone within the contraceptives, have little effect on breast cancer risk. Women who begin use before age 20 have higher relative risks of having breast cancer diagnosed while they are using combined oral contraceptives and in the 5 years after stopping than do women who begin use at older ages. Given that on influence of oral contraceptives on the breast has been hypothesized to be greatest before the cellular differentiation that occurs with a first pregnancy. A significant trend of increasing risk with first use before age 20 years was observed. Among women diagnosed at ages 30 to 34 years the relative risk associated with recent oral contraceptive use was 1.54 if use began before age 20 years and 1.13 it use began at older ages.