Background: The relationship between mammographic density and the risk of breast cancer was examined in Japanese women. The study was a matched case-control study comparing the mammographic densities of both breast cancer cases and healthy controls.
Materials and methods: We selected 237 women who were diagnosed with a histologically verified breast cancer, and who underwent surgery at Gihoku General Hospital in Gifu, from January, 1998 to December, 1999. During the time of this study, 3,650 people participated in breast cancer screening with mammography and ultrasound together. We selected 742 women as a control group from the screening participants and matched them by age and the number of deliveries with the cancer patients. The same mammography machine was used for both cases and controls. For evaluation, we used a visual method (Wolfe's classification) and a computer assisted method to classify the mammograms based on mammographic density.
Results: (1) According to Wolfe's classification, the DY group had a significantly increased breast cancer risk compared with the N1 group (Relative risk (RR)=2.20, 95% confidence interval (95%CI) (1.02-4.77). (2) The group showing a high mammographic density had a significantly increased risk of breast cancer compared with the group with low mammographic density (RR=2.83, 95%CI=1.33-5.98) as classified by the computer assisted method.
Conclusion: It is suggested that women with high mammographic densities, classified visually or by computer, have an elevated risk of breast cancer compared with those with low mammographic densities.