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Breast Density: An Important Predictor of Breast Cancer?

Models estimating breast cancer risk are improved when breast density is included.

The Gail model for estimating breast cancer risk was developed almost 2 decades ago using retrospective data. Calculation of risk with this model takes several factors into account (see Table 1 and http://www.cancer.gov/bcrisktool/Default.aspx). Nonetheless, the Gail model is considered to be only mediocre in its ability to predict breast cancer in individual women. To determine whether other factors are also important in assessing breast cancer risk, these investigators analyzed data from seven geographically diverse mammography registries in the U.S., based on screening mammograms performed from 1996 through 2002. Women age 35–84 years with no history of breast cancer were included in this analysis. A cancer diagnosis was recorded if in situ or if invasive breast cancer was diagnosed within 1 year of screening. Almost 2.4 million screens from more than 1 million women were included; breast cancer was diagnosed in 11,638 women (4.86 breast cancers per 1000 screens).

For both pre- and postmenopausal women, age and mammographic breast density were found to be the factors most strongly associated with breast cancer risk. Other risk factors for premenopausal women included prior cancer-related procedure to the breast and first-degree family history of breast cancer. For postmenopausal women, additional risk factors included family history, elevated BMI, prior false-positive mammogram, and prior breast procedure; white or black ethnicity was associated with higher breast cancer risk than was Native-American, Asian, Hispanic, or Pacific Islander ethnicity. Overall, the investigators found that breast density as a single risk factor was almost as strongly predictive of risk as was age.

Comment: Women whose risk factors make them more likely to develop breast cancer should be encouraged to undergo additional breast imaging and genetic evaluation, and to consider chemoprophylaxis or surgical prophylaxis. These results suggest that new breast cancer prediction models should include breast density. However, as editorialists point out, it may be premature to jump on the breast density bandwagon without adequate preparation: There is current uncertainty regarding how best to report density, and many mammography facilities do not routinely assess this characteristic in a standardized fashion.

— Andrew M. Kaunitz, MD

Published in Journal Watch Women's Health October 19, 2006

Citation(s):

Barlow WE et al. Prospective breast cancer risk prediction model for women undergoing screening mammography. J Natl Cancer Inst 2006 Sep 6; 98:1204-14.

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• Medline abstract (Free)

Bondy ML and Newman LA. Assessing breast cancer risk: Evolution of the Gail Model. J Natl Cancer Inst 2006 Sep 6; 98:1172-3.

• Original article (Subscription may be required)
• Medline abstract (Free)