Mammographic density (MD) is a strong risk factor for breast cancer. We examined the association between annual MD change and risk of breast cancer, and how adding annual MD change to baseline measure of MD influenced risk prediction of breast cancer.
We used the Karolinska Mammography Project for Risk Prediction of Breast Cancer (KARMA) cohort (N = 43,347 Swedish women), with full access to risk factors for breast cancer and pre-diagnostic mammograms. MD was measured as dense area (cm2) using the STRATUS method. We calculated the relative MD area change between repeated examinations. Relative MD area change was categorized as stable (less than 10% decrease per year) and decrease (more than 10% decrease per year). Cox proportional hazard regression (HR) estimated the association of breast cancer with MD change. Interaction analyses investigated how relative MD change modifies the association between baseline MD and breast cancer risk. All statistical tests were two-sided.
Women who did not experience a MD decrease over time had a 27% significantly increased risk of breast cancer (HR = 1.27; 95% CI = 1.02 to 1.59) compared to those who decreased by at least 10% per year. The increased risk was confined to postmenopausal women. Stratifying women based on baseline MD did not seem to add to risk prediction with the exception of women in the lowest baseline MD group where women did not experience a MD decrease had a 74% higher risk (HR = 1.74; 95% CI = 1.10 to 2.75), again only seen in postmenopausal women.
Our results suggest that annual MD change influences breast cancer risk in postmenopausal women but that adding MD change to baseline MD do not seem to substantially improve breast cancer risk prediction.
Per Hall (Principle investigator).
Märit and Hans Rausing’s Inititive Against Breast Cancer.
All authors have declared no conflicts of interest.