What Is patientINFORM?

Summary: Digital mammograms may be better than conventional film mammograms at detecting breast cancer in women under age 50, women who have not gone through menopause, and those with dense breasts, results of a new study suggest. The digital x-rays found cancers regular mammograms missed in these women, says the report in the New England Journal of Medicine.

Why it's important: Breast cancer is the most common cancer in US women after skin cancer. Mammograms, which are x-rays of the breast, are the best tool available for detecting breast cancer early, when it is more easily treated. But standard film mammograms can't always see through dense breast tissue, so these tests are less precise for some women. Using digital images may be one way to improve the accuracy of mammography and catch more cancers.

What's already known: Digital mammograms offer some advantages over regular film mammograms because doctors can use a computer to manipulate the image -- by adjusting contrast, for instance -- to see the breast more clearly. Despite that, previous comparisons of digital and conventional mammograms have not found significant differences between the two methods. However, these earlier studies only used one type of digital mammography machine and didn't include enough women to find small, but important, differences in accuracy.

How this study was done: Researchers at multiple institutions recruited more than 49,000 women with no signs of breast cancer to get both a digital and a standard mammogram. Five different digital mammography machines were used. Two separate doctors read the mammograms, and the results of each were compared. The women were asked to return after a year for a follow-up mammogram.

What was found: The researchers found breast cancer in 335 women. When they looked at all of the women together, digital and conventional mammography performed about the same. But when they separated the women into groups by age and other characteristics, they noticed some important differences.

Digital mammography was better at finding cancers in women under age 50, women with dense breasts, and women who had not yet reached menopause or who were just approaching menopause. These are exactly the groups of women in whom standard mammograms tend to miss cancers, said lead study author Etta Pisano, MD, a professor of radiology and biomedical engineering at the University of North Carolina at Chapel Hill. What's more, the types of tumors found in these women were potentially dangerous ones.

"The cancers detected only by digital mammography are the types of cancers that must be detected early to save more lives through screening," Pisano said in a statement.

Race, the type of cancer a woman had, and the type of digital mammography machine used did not make a difference in detection. Likewise, digital mammograms didn't give any advantage to women who fit all of these criteria: over age 50, did not have dense breasts, and already in menopause.

Study limitations: The study, which was funded by the National Cancer Institute and conducted by the American College of Radiology Imaging Network, did not look at deaths from breast cancer. It does not tell us if women whose cancer was found by a digital mammogram will ultimately fare any better or worse than women whose cancer was found by a standard film mammogram. But the researchers say that if digital mammography performs as well as standard mammography, as appears to be the case, then it probably reduces breast cancer deaths by finding the disease early just as standard mammography does.

But neither technique is perfect, they warn. Both digital and conventional mammograms missed some breast cancers in the women in the study. For this reason, it's important for women to get any lumps or other symptoms checked by a doctor right away, even if their mammogram was clear.

The bottom line: Pisano said the study results will give doctors and patients better guidance in deciding which type of mammogram to get. Robert Smith, PhD, director of screening for the American Cancer Society, also said the results are important and "should lead to improvements in screening programs if digital mammography is targeted to women who are likely to benefit the most." Smith was not involved in the research.

However, digital mammogram machines are still rather rare in the US; only about 8% of breast imaging centers have them, according to the NCI. That's because they are still very expensive compared to traditional film mammogram machines. Both types of mammograms are covered by Medicare.

Smith said the important thing is for women to get regular mammograms, no matter which technology they use. ACS recommends that women start getting a yearly mammogram at age 40, or even younger if they are at high risk of developing breast cancer.

"Younger women and women with denser breasts should not forego their regular mammogram if digital mammography is not available," he cautioned. "While this study showed an advantage with digital imaging in these groups, it should be remembered that traditional film mammography also is effective."

Citation: "Diagnostic Performance of Digital versus Film Mammography for Breast-Cancer Screening." Published online September 16, 2005, in the New England Journal of Medicine. First author: Etta D. Pisano, MD, University of North Carolina at Chapel Hill.