Mammography is probably the most important tool doctors have to help diagnose breast cancer and follow women who’ve had it. Safe and highly accurate, a mammogram is an X-ray photograph of the breast. Leading experts, including the National Cancer Institute, the American Cancer Society, and the American College of Radiology, recommend a mammogram every year for women age 40 and older.

But mammograms aren’t perfect. Normal breast tissue can hide a breast cancer, so that it doesn’t show up on the mammogram. This is called a false negative. And mammography can identify an abnormality that looks like a cancer, but turns out to be normal. This “false alarm” is called a false positive.

There are two types of mammograms:

• Film mammograms: A skilled technologist positions and compresses the breast between two plates. Then a highly specialized camera takes two pictures of each breast from two directions. This technique has been used successfully since the 1960s.
• Digital mammograms: Digital mammography uses the same technique as film screen mammography, except that the image is recorded directly into a computer. The image can then be enlarged or highlighted. This new technology is more expensive than film mammography and not as widely available. About 8% of breast imaging centers in the United States offer digital mammograms.

In the study reviewed here, researchers wanted to see if film mammograms and digital mammograms differed in accuracy of results. Earlier studies showed no differences, but those studies were small.

Study design: The Digital Mammographic Imaging Screening Trial included 49,528 women from across the United States and Canada. The women in the study

• had no signs or history of breast cancer,
• were not pregnant, and
• did not have breast implants.

On their appointment day, the women had both a film mammogram and a digital mammogram, with at least two views of each breast taken during each mammogram. The women also provided background health information and information on their:

• age,
• race, and
• menopausal status.

Two different certified radiologists interpreted both types of mammograms for each woman. Results from 42,760 women were analyzed.

The study was funded by the National Cancer Institute and was coordinated by a group of researchers from the American College of Radiology Imaging Network.

Results: The researchers found that digital mammography was significantly better at detecting breast cancers than film mammography in three groups of women:

• women who were younger than 50,
• women who had dense breasts, and
• women who were pre-menopausal or peri-menopausal (had had their last period within a year of their mammograms).

These results were statistically significant, meaning that they were most likely due to the extra benefits of digital mammography and not just to chance.

The researchers found that digital mammograms had NO benefit over film mammograms for women who were:

• older than 50, AND
• did not have dense breasts, AND
• were post-menopausal.

When the researchers looked at ALL the women in the study, they found that digital mammograms and film mammograms had very similar levels of diagnostic accuracy (about 70%). The researchers also found that film and digital mammography were equally accurate for women regardless of:

• race, or
• risk of developing breast cancer.

As a result of the mammograms taken during the study, 335 women were diagnosed with breast cancer. In general, film mammograms and digital mammograms found cancers that were similar in stage.

But the cancers FOUND by digital mammography and MISSED by film mammography in:

• Women younger than 50
• Women who had dense breasts
• Women who had their last period within a year of their mammograms

were either invasive or medium- and high-grade non-invasive cancers. Many of these cancers had not spread to the lymph nodes. The digital mammograms found these more serious cancers early, which means treatment could begin.

Neither digital or film mammograms found all the breast cancers in the women in the study.

Conclusions: The researchers concluded that a digital mammogram is more accurate in finding breast cancer than a film mammogram for women who are younger than 50, have dense breasts, or who still have their periods (or have had a period within the past year).

The researchers recommended that women who are NOT in one of these three categories continue to have annual film mammograms. Film and digital mammograms were equally accurate for these women.