Asymmetric Dense Breast is an Independent Breast Cancer Risk Factor

Objectives: There are multiple known breast cancer risk factors, but most women with breast cancer do not have any of them, so there should be some other unknown risk factors. We hypothesized that asymmetric breast densities could be another breast cancer risk factor. Method: In this study, we defined two case and control groups with 136 women with breast cancer and 136 who did not have breast cancer, respectively. Any different type of asymmetry in either breast was recorded in both groups. Result: The frequency of focal asymmetry in cases was 47 (34.6%), which was statistically more significant than in the control group (28 (20.6%)) (p=0.010). There were three (2.9%) and five (3.7%) global asymmetries in the case and control groups, respectively (p=0.735). The frequency of one view asymmetry in the case and control groups was not significant (16 (11.8%) and 9 (6.6%) respectively) (p=0.142). In the case group, 59 (43.4%) women had at least one type of asymmetry, compared to 41 (30.1%) in the control group (p=0.02). We identify focal asymmetries (likelihood ratio, 1.215; p=0.027) is risk factors for breast cancer. Conclusion: Breast density asymmetry is a breast cancer risk factor that could be scored, thus enhancing risk stratification for screening and prevention.