Quantitative assessment of mammographic density and breast cancer risk for Japanese women.

We conducted a case-control study to examine the relationship between breast density (BD) on mammography and breast cancer risk for postmenopausal Japanese women. The mammograms (205 cases and 223 controls) were classified by two doctors employing Wolfe's classification and used to measure BD with original computer software. A weak relationship between breast cancer risk and the parenchymal pattern of Wolfe's classification was found. The BD measured with the computer software, however, showed a significant relationship with breast cancer risk. Analysis after adjustment for epidemiologic factors showed that women in the quintile with the highest BD had a 3.02 times higher risk of breast cancer than those in the quintile with the lowest density. Since mammographic BD is clearly associated with breast cancer risk for postmenopausal Japanese women, our software can be expected to become a useful tool for objective risk assessment of breast cancer.