Breast cancer in young women and use of oral contraceptives: possible modifying effect of formulation and age at use.

A case-control study of 314 breast cancer patients aged less than 37 at diagnosis and 314 individually matched controls was done to assess the influence of oral-contraceptive (OC) use on the risk of the disease. Long-term use before age 25 of combination-type OCs with a "high" content of the progestogen component was associated with increased risk of breast cancer: the relative risk was approximately 4 after 5 years of such use, and 9 cases and no controls had used such combination-type OCs for more than 6 years before age 25. Use of combination-type OCs with a "low" progestogen component appears to increase breast-cancer risk little or not at all.