Dense breasts can make traditional film mammograms difficult to interpret because both tumors and dense breast tissue appear as solid white areas. A recent study revealed that, in some women with dense breasts, digital mammograms are better able to detect cancer.

Dr. Etta D. Pisano from the University of North Carolina School of Medicine at Chapel Hill and her colleagues evaluated 49,528 women from 33 centers across the US and Canada to see whether, for any of the women studied, digital mammography was superior to film. The researchers detected breast cancer status (as a reference standard) in 42,760 of the women from either biopsy results or from postclinical follow-up 10 months after the initial imaging.

As reported in the February issue of Radiology, the investigators divided the women into 10 subgroups for comparison based on age (younger than 50 years old, between 50 and 64, and 65 or older) and on breast density (two categories of very dense breasts and two of the least dense). Every woman was screened with both film and digital mammography.

The researchers discovered that digital mammograms were better able to detect cancer in pre- or perimenopausal women with dense breasts who were younger than 50 years old. They used a special seven-point scale created for this study to obtain comparison values under a curve and found that the value for digital was 0.79 as opposed to 0.54 for film. They also found that the sensitivity for digital was 59 percent as compared with 27 percent for film. The values were not significantly different for any of the other subgroups. However, the investigators discovered a nonsignificant trend toward film being superior to digital in women over 65 with fatty breasts.

The researchers could not determine why the digital mammograms were superior to film for just one particular group of women. However, they are analyzing image characteristics in digital and film mammography to see whether certain ones explain the variation in diagnostic accuracies for various populations.