A new study has reported that there are strong associations between breast density and the risk of breast cancer. The study included 1,025 breast cancer patients and 520 healthy women (the controls) from whom mammograms were obtained. Mammographic percent density (0%-100%) was measured. The breast cancer patients were found to have higher breast density than the healthy controls (38% compared to 32%). Age over 60 years, body mass index (BMI) of 25 to 30 kg/m2 (overweight), no history of childbirth or low number of births (one to two) were associated with significantly higher breast density. Average mammographic density was found to be lower as age, BMI, and number of children increased. On the other hand, breast density tended to be higher the older the age at first full-term pregnancy.

Breast density was higher in women with at least one first-degree relative (parent, sibling or child) with breast cancer, but only among the breast cancer patients and not among the healthy women. This implies that women with a family history of breast cancer and low breast density may not have as high a risk of breast cancer as those with high density. The risk of breast cancer was twice as high in women with mammographic density of 25% or more than women with density of less than 10% in the overall study group. When only the postmenopausal women were considered, the risk of breast cancer was nearly tripled among those with density of at least 25%. The study provides further evidence that mammographic density is an important risk factor for breast cancer.

Please see our article on breast density and breast cancer for more information on how diet and other factors can influence breast density.