Abstract
We evaluated risk factors for benign breast disease by using a case-control study method. The series was taken from participants in breast cancer screening programs during 1978-1986 in Miyagi Prefecture, Japan. All benign breast lesions diagnosed during this period were reviewed and reclassified into proliferative and non-proliferative types based on the Dupont and Page classification. Data on 382 benign breast disease cases (130 proliferative-type cases and 252 non-proliferative-type cases) and 1,489 screening year-, age- and screening area-matched normal controls were used for analysis. Nulliparity or low parity and family history of breast cancer in mother or sisters were significantly associated with an increased risk of proliferative type. Premenopausal status was significantly associated with an increased risk of non-proliferative type. No significant association with history of lactation for the last child was observed in either type, but the risk of proliferative type increased with increasing duration of lactation (P=0.08). A comparison between the present findings and the risk factors for breast cancer indicated epidemiologic similarities between proliferative benign and malignant breast lesions in general. The associations of these two lesions with lactation patterns were, however, dissimilar.