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Mammographic Density and Breast Cancer

As expected, the risk was highest among women with extremely dense breast tissue.

Mammographic breast density is associated with breast cancer via two mechanisms: (1) dense tissue appears to reflect a biologic predisposition to breast cancer, and (2) dense tissue masks tumors on mammography. In this Canadian study, researchers determined the relative contributions of these two mechanisms to breast cancer risk.

Drawing from mammographic screening studies, researchers assembled 1112 cases (women with newly diagnosed breast cancer) and 1112 age-matched controls. In analyses adjusted for conventional risk factors, women with extremely dense breasts on mammography had a significantly increased risk for mammography-detected breast cancer, compared with women in the lowest-density category (odds ratio, 3.5). During the 12 months after a negative mammogram, women with extremely dense breasts had an even greater risk for being diagnosed with breast cancer (OR, 17.8), compared with women in the lowest-density category. The latter finding implies that breast cancers were frequently masked by dense breast tissue (resulting in a negative mammogram) but became palpable or symptomatic shortly thereafter. Breast density was a particularly strong risk factor in women younger than 56.

Comment: These findings support the concept that breast density not only indicates increased risk for breast cancer, but also decreases the sensitivity of mammography. Many radiologists now report breast density on screening mammograms, and predictive models incorporating breast density as a risk factor are being developed (Journal Watch Sep 26 2006). Prospective trials are needed to determine whether this information can be used to reduce risk and improve detection.

— Allan S. Brett, MD

Published in Journal Watch General Medicine January 17, 2007

Citation(s):

Boyd NF et al. Mammographic density and the risk and detection of breast cancer. N Engl J Med 2007 Jan 18; 356:227-36.

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

Kerlikowske K. The mammogram that cried Wolfe. N Engl J Med 2007 Jan 18; 356:297-300.

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