Inverse association between risk factors for benign and malignant breast lesions.

The purpose of the present study was to compare the risk of breast cancer and the risk of benign breast disease using known risk factors for breast cancer. The series was taken during breast cancer screening of women aged 41-60 in an industrial city in Finland. 158 breast lesions were diagnosed, 27 of which were malignant. Women with breast disease and 534 controls were interviewed to obtain epidemiological data. The prevalence of benign lesions decreased after menopause but the prevalence of carcinomas was essentially the same over the age span 41-60. Several risk factors for breast cancer, such as selected reproductive and hormonal characteristics, were not associated with the risk of benign breast disease. Thus it was concluded that benign and malignant breast lesions are not associated in general, and the decrease in the prevalence of benign breast lesions after menopause is more likely to be due to regression than to transition to carcinoma.