Women with high mammographic breast density have more than four times the risk of breast cancer compared to those with less dense breasts (which have a higher percentage of fat). In fact, high breast density is one of the strongest risk factors for breast cancer. Breast cancer survivors with dense breasts are at heightened risk for developing new tumors in the opposite breast, as well as in the same breast if it was treated by lumpectomy without subsequent radiotherapy. However, high breast density does not appear to be associated with increased risk of distant metastasis. Now a new study has reported that survivors with high mammographic breast density do not have an increased risk of death from breast cancer.

High breast density increases risk of breast cancer and local recurrence

Women with a family history of breast cancer tend to have dense breasts, which partially explains their increased risk of breast cancer. As noted above, women with dense breasts have a higher rate of second primary breast cancer (a new tumor that arises after treatment and that does not appear to be directly related to the first breast cancer). Breast density is influenced by diet and other factors. Women with a reduction in breast density over time have been shown to have a reduction in breast cancer risk compared to women whose breast density remains stable.

While breast density is one of the strongest risk factors for breast cancer, it does not appear to influence tumor development in very specific ways. Having dense breasts heightens the risk of both ductal and lobular breast cancer. Dense breasts have been shown to be associated with hormone receptor positive (ER+/PR+) and mixed hormone receptor (ER+/PR- and ER-/PR+) tumors. Studies have reported conflicting results for hormone receptor negative (ER-/PR-) tumors. It is possible that breast density acts as a general stimulator of tumor development, interacting with other risk factors to determine hormone receptor profile.

Given the higher risk of local recurrence (in the same or opposite breast), systemic treatment such as chemotherapy or endocrine treatment appears to make sense for women with dense breasts. This holds even if the tumor is small.

Latest research finds that breast density does not predict survival

The study referenced at the beginning of this news article was designed to investigate the relationship between mammographic breast density and risk of death among breast cancer survivors. The study included 9,232 women in the US Breast Cancer Surveillance Consortium who were diagnosed with invasive breast cancer between 1996 and 2005. Participants were followed for an average of 6.6 years. Mammographic breast density was determined using the Breast Imaging Reporting and Data System (BI-RADS) density classification. Women with normal density (scattered fibroglandular densities (BI-RADS 2)) were the comparison group. The analyses took into account tumor site, age and year of diagnosis, stage, body mass index (BMI), mode of detection (primarily screening mammogram or self-detection), type of treatment, and income level.

A total of 1,795 study participants died during follow up 889 died of breast cancer and the remaining women died of other causes. High breast density (BI-RADS 4) was not found to be associated with risk of death from breast cancer or death from other causes. The results held when analyzed according to tumor stage and other prognostic factors, apart from a finding of increased risk of death from breast cancer among women with low breast density (BI-RADS 1) who were either obese or had tumor size ≥ 2.0 cm. The authors conclude that high mammographic breast density is not associated with risk of death from breast cancer or death from any cause after accounting for other patient and tumor characteristics. The authors comment that the study results demonstrate that risk factors for breast cancer development do not always influence the risk of death after breast cancer is established.

Please see our article on breast density for more information.