The Effects of Age, Breast Density, and Hormone Therapy on the Accuracy of Screening Mammograms

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The summary below is from the full report titled "Individual and Combined Effects of Age, Breast Density, and Hormone Replacement Therapy Use on the Accuracy of Screening Mammography." It is in the 4 February 2003 issue of Annals of Internal Medicine (volume 138, pages 168-175). The authors are PA Carney, DL Miglioretti, BC Yankaskas, K Kerlikowske, R Rosenberg, CM Rutter, BM Geller, LA Abraham, SH Taplin, M Dignan, G Cutter, and R Ballard-Barbash.

What is the problem and what is known about it so far?

Mammograms are special x-rays of the breast that can identify breast cancers before a woman or her doctor can feel a lump in the breast. However, mammograms are not totally accurate. They sometimes suggest a cancer when it is not present (a false-positive result). Other times, mammograms look normal even though a cancer is present (a false-negative result). Younger women's breasts contain less fat and are denser than older women's breasts. In addition to age, breast density is affected by hormones, such as combinations of progestin and estrogen or estrogen alone. When a woman takes these hormones, her breasts become less fatty and denser. Mammograms of dense breasts are harder to read than mammograms of fatty breasts. However, the way that breast density, age, and hormone therapy influence the accuracy of mammograms (alone and in combination) is not well understood.

Why did the researchers do this particular study?

To learn how breast density, age, and hormone therapy (alone and in combination) affect the accuracy of screening mammograms.

Who was studied?

329,495 women between 40 and 89 years of age who had mammograms from 1996 to 1998 in several U.S. cities and states.

How was the study done?

The researchers looked at the results of the women's mammograms and whether the breast cancer was eventually diagnosed. They then looked at the accuracy of the mammogram in relation to a woman's age, breast density, and whether she was taking hormone therapy.

What did the researchers find?

The accuracy of mammograms increased as women's breasts became more fatty and less dense. Mammograms were also more accurate as women aged. The accuracy of mammograms was the same for users and nonusers of hormone therapy, as long as the researchers accounted for breast density and age. Hormone therapy by itself did not affect the accuracy of mammograms; however, by its effect on breast density, it affected mammogram accuracy.

What were the limitations of the study?

The study used information from a mammogram registry; thus, information on some women was missing.

What are the implications of the study?

Mammograms are less accurate in young women than in older women and in women with dense breasts than in women with fatty breasts. While hormone therapy may increase breast density, it will not affect the ability of mammography to detect cancer if it is present. However, women with dense breasts may need additional imaging studies to confirm the presence of cancer.