June 11 (HealthDay News) -- The accuracy of mammography screening is affected by certain characteristics of the facility where it's performed, a U.S. study finds.

Researchers looked at data from 44 sites that performed 484,463 screening mammograms on 237,669 women between 1992 and 2002.

Of those women, 2,686 were diagnosed with breast cancer. On average, breast cancer was identified when it was present (sensitivity) in 79.6 percent of breast cancer cases that occurred within one year. Mammograms were correctly identified as cancer-free (specificity) 90.2 percent of the time.

The likelihood of cancer in women who were referred for additional imaging or evaluation due to an abnormal mammogram was 4.1 percent. On average, 38.8 percent of women referred for a biopsy were found to have cancer.

The analysis revealed that the likelihood of cancer among women with any additional evaluation, or those referred for biopsy, varied substantially between facilities. There were also differences in the probability that a mammogram was accurately read as cancer-free, but no variations in the likelihood that a cancer was identified when it was present.

Certain kinds of facility had a higher measure of mammogram screening accuracy, including those that offered screening mammograms only versus those that offered diagnostic and screening mammograms, and those that had a breast imaging specialist reading the mammograms versus those that did not.

The study was published in the June 10 issue of the Journal of the National Cancer Institute.

If these findings are confirmed in future studies, they could help both patients and mammography facilities, Dr. Stephen Taplin, of the National Cancer Institute, said in a prepared statement.

"Understanding how facility characteristics influence interpretive accuracy is important, because it could allow women and physicians to choose a mammography facility based on characteristics that are more likely to be associated with higher quality. Radiologists could also change the facilities' structures or processes to included practices that improve interpretive accuracy," the study authors wrote.

Previous research has shown that patient characteristics, such as age, and the experience and other characteristics of the radiologist who interprets the mammograms, affect the accuracy of screening mammograms.

SOURCE: Journal of the National Cancer Institute, news release, June 10, 2008