Digital mammography better screening tool for some women

Patients are cautioned against postponing an annual mammogram while awaiting a digital machine to arrive at their local screening site.

By Susan J. Landers — Posted Oct. 17, 2005

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Washington -- Digital mammography more accurately detected breast cancer among women whose breasts are dense than did standard film mammography, according to findings from a large, multicenter trial sponsored by the National Cancer Institute.

In general, the women who stand to benefit from this technology, which is now available in only about 8% of mammography facilities nationwide, are younger than 50 and premenopausal or perimenopausal.

For women in other categories, a comparison between digital and film mammography showed no difference in detecting breast cancer. The results of the randomized controlled trial of nearly 50,000 women were published online by the New England Journal of Medicine as they were announced at a Sept. 16 meeting of the American College of Radiology Imaging Network in Arlington, Va.

For women, breast cancer is the most common non-skin cancer and the second leading cause of cancer-related death in the United States. More than 211,000 women in the nation will be found to have invasive breast cancer this year, and about 40,410 will die. Death rates from breast cancer are, however, dropping, and earlier detection is believed to be playing a role.

The findings from the new study were welcomed by many for providing another screening option for women with dense breasts who might not have been well-served by film mammography. The types of lesions found by digital mammography and not by film among these women were the types of cancers that can lead to death, the researchers said. They were invasive cancers without evidence of metastasis to auxiliary lymph nodes at time of diagnosis and medium and high-grade in situ lesions.

The new technology "gives physicians and patients perhaps a better chance for earlier detection," said Cheryl Perkins, MD, senior clinical adviser at the Susan G. Komen Breast Cancer Foundation. "In this group of women, there have been problems with the accuracy of mammograms."

Earlier studies indicated that about 10% to 20% of breast cancers that were detected by a physical examination were not visible on film mammography.

A digital future

While praising the benefits of digital, physicians were careful to avoid downplaying film mammography's continued contribution to reducing breast cancer's toll. It is still a "gold standard" screening tool, Dr. Perkins noted.

"The important thing is that women receive mammograms on a regular basis, regardless of which technology they use," said Robert Smith, PhD, the American Cancer Society's director of cancer screening. "Younger women and women with denser breasts should not forgo their regular mammogram if digital mammography is not available."

Nonetheless, many see digital mammography as the way of the future -- despite its high cost. A digital machine is as much as four times as expensive as a film machine.

"You can enhance your images, you can take different views, it's easier to store images, and it's easier to share information from one provider to another," Dr. Perkins said. Once a film mammogram is obtained, it cannot be significantly altered. If the film is underexposed, for example, contrast is lost and cannot be regained.

"We try to screen everyone digitally," said Nagi Khouri, MD, director of breast imaging at Johns Hopkins Breast Center in Baltimore, which had acquired the digital technology three years ago. Johns Hopkins also served as one of the 33 centers in the study in which Dr. Khouri served as an investigator.

"We favor the machine -- it's much more streamlined. You don't have to run to the darkroom to develop the film, and there are no dust artifacts," he said. Those advantages coupled with its better results for certain groups of women "signal to me that mammograms will go digital."

Dr. Khouri also believes that women soon will be asking for a digital mammogram whether or not there is a benefit for them. "It will be important not to create a panic and say, 'If you have an analogue mammogram it's no good.' "

Physicians will likely have to step in as educators to guide women to the appropriate screening tool, Dr. Perkins said.

And technology already has moved the screening field beyond digital vs. film mammography to include the use of ultrasound and, for women at high risk genetically, MRIs. "Knowing when to use these tools and for which populations they are most useful can only add accuracy to the whole process," Dr. Perkins said.

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Digital mammographic imaging screening test

This study began in October 2001 and enrolled 49,528 women who had no signs of breast cancer at 33 sites in the United States and Canada. Here are the specifics:

  • All women had a digital and film mammogram on the same day, each with a minimum of two views of each breast.
  • Two different certified radiologists interpreted the conventional and digital mammograms for each patient.
  • The results suggest that for women who fall into three subgroups (women younger than 50, women with heterogeneously dense or extremely dense breasts, and pre- and perimenopausal women), digital mammography may be better at detecting breast cancer than traditional film mammography.
  • Approximately 65% of the women in DMIST fit into one of the three subsets that showed a benefit with digital mammography.

Sources: National Cancer Institute; New England Journal of Medicine, Oct. 27

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External links

National Cancer Institute on results from the Digital Mammographic Imaging Screening Trial (link)

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