1. A significantly slower rate of breast density decline over time was observed in the breast that developed cancer when compared with controls.
2. Mean volumetric density of both breasts at the entry to study was higher in case-cohort women as compared with control group women.
Evidence Rating Level: 1 (Excellent)
Study Rundown: There is an association between breast density and breast cancer, but information regarding the relationship between the rate of change in density and breast cancer risk is limited. This study investigated the association between the natural decline in breast density with age and the risk of developing breast cancer. The primary outcome of this study was the rate of change of breast density in women from either the case (developed breast cancer) or control cohort (did not develop breast cancer). It was noted that breast density declined in all post-menopausal women in the study. The mean volumetric density of both breasts at the entry to the study was higher by a significant margin in women from the case group as compared to the control group. When considering the mean volumetric breast density of both breasts, there was no difference between the case and control cohort women. However, when considering the density of each breast separately, a slower rate of decline in density was observed in the breast which subsequently developed cancer. Limitations to this study include that the majority of women in the study were of Caucasian background, however, it has been noted that breast density as a risk factor is consistent among nationalities. Additionally, the mammographic images collected for the study were from a single manufacturer, but previous studies have concluded consistency across manufacturers. Overall, the results from this study suggest that the consideration of longitudinal breast density changes may be helpful in screening for breast cancer in appropriate populations.
Click to read the study in JAMA Oncology
Relevant Reading: Changes in mammographic density over time and the risk of breast cancer: an observational cohort study
In-Depth [case-control study]: This prospective, nested case-control study based out of a single centre in the United States considered the mammographic data collected from 10,481 women. Of these women, 347 were identified as having incident breast cancers, 289 of which met study parameters and a 2:1 control: case ratio was followed; 694 women were identified as appropriate controls, 658 of whom were retained for study analysis. The mean volumetric density of both breasts was significantly denser in case-cohort women than in control-cohort women (estimate = 0.140; 95% confidence interval (CI), 0.033-0.246. The longitudinal change in density was not different between groups when considering the mean density of both breasts (estimate = 0.018; 95% CI, -0.004-0.039), however, when these longitudinal changes in density were examined in each breast separately, a slower rate of breast density decline was recorded in the breast that subsequently developed cancer when compared with controls (estimate = 0.027; 95% CI, 0.001-0.053).
Image: PD
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