Women with lumps in their breasts rely on their radiologists to accurately read their mammograms, but the accuracy of those readings varies widely, US researchers reported. Women with lumps in their breasts rely on their radiologists to accurately read their mammograms, but the accuracy of those readings varies widely, US researchers reported on Tuesday.

Earlier studies found variation in the quality of screening mammograms. But the new research found inconsistencies even when a lump was present, leaving some women open to false positive results or even missed diagnoses, said Diana Miglioretti, a researcher at the Group Health Center for Health Studies in Seattle, whose study was published in the Journal of the National Cancer Institute.

Miglioretti and her team evaluated 123 radiologists who looked at 36,000 diagnostic mammograms from 1996 through 2003 at 72 US facilities, including six from Group Health, a nonprofit health maintenance organization in Washington.

They found that sensitivity -- the ability to accurately detect cancer -- ranged from 27 to 100 per cent. False positives ranged from 0 to 16 per cent.

"On average, 21 per cent of breast cancers were missed and 4.3 per cent of women underwent a biopsy even though they didn't have breast cancer," Miglioretti said in a telephone interview.

This variability was evident even after accounting for differences in physical characteristics.

Miglioretti said the results surprised her.

"I was expecting diagnostic mammograms to be less variable than screening mammograms," Miglioretti said. Diagnostic mammograms are those performed on women whose initial, screening mammograms raise concern about the possibility of cancer.

The study included data from rural hospitals, where radiologists may not handle a high volume of diagnostic mammograms.

Miglioretti said women might want to consider scheduling diagnostic exams at centers with breast imaging experts. "It might be worth driving the extra hour to find one. It is not always possible," she said.

The study was funded by grants from the National Cancer Institute, Agency for Healthcare Research and Quality and Breast Cancer Surveillance Consortium.

There will be an estimated 178,000 new cases of breast cancer in the United States this year, with 40,000 deaths.