Risk factors for benign breast disease.

The importance of various risk factors for benign breast disorders has been assessed an analysis of data obtained from a multicenter cohort study of contraceptive use among women in the United Kingdom (the Oxford Family Planning Association Contraceptive Study). Cases comprised all women diagnosed as having any type of benign breast lesion; 74 had fibroadenoma, 211 had histologically confirmed chronic cystic disease, 331 had breast lumps not subjected to biopsy and 70 had other disease. Each case was individually matched with another study participant who was free from recognized breast disease. Matching factors were center of recruitment, date of recruitment, age at entry, and continuation in the study. An inverse association was found between use of oral contraceptives and the risk of the first three conditions. Current users of the pill had the lowest risk, particularly when the use was for an extended period. In contrast, past users demonstrated no reduction in risk. The reduction in risk for chronic cystic disease appeared to relate to the amount of progestogen contained in the pill. No significant association was observed between the risk of any of the conditions and either parity or age at first livebirth. Women of low social class and obese women were at low risk, perhaps reflecting diagnostic biases.