Risk of Breast Cancer in Japanese Women with Benign Breast Disease

To investigate the risk of breast cancer development in women with benign breast disease (BBD), 387 screen‐detected BBD women and 1,489 normal women, taken from participants in the breast cancer screening program during 1978–1986, were followed through 1991. While 2,811 person‐years in the BBD group and 11,018 person‐years in the normal group were accumulated, 5 women in the BBD group and 6 women in the normal group developed breast cancer. Using the Mantel‐Haenszel method, relative risks (RR) were estimated for all women with BBD and women in some BBD types. Significantly elevated risk of breast cancer was observed in all women with BBD (RR=3.26, 95% confidence interval (CI) 1.08−9.83). Women with proliferative BBD were at high risk of breast cancer (RR=8.48, 95%CI 2.99−24.10), but no increased risk was observed for women with non‐proliferative BBD (RR=0.93, 95%CI 0.11−7.66). These results are consistent with those in high‐risk countries for breast cancer. In the management of women with BBD, histopathological diagnosis of the breast lesion is essential and women with proliferative BBD should be followed up carefully.