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Missed Breast Lesions Found After the Fact

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Nov. 30, 1999 (Chicago) -- Radiologists often say that it is difficult to find very small lesions in dense breasts --which the breasts of younger women often are -- with mammograms, but a study from Stanford University radiologists suggests that about half of the "missed" cancers are found in non-dense, or fatty, breasts.

Robyn L. Birdwell, MD, assistant professor at the Stanford University School of Medicine, reported the finding at the 85th Scientific Assembly and Annual Meeting of the Radiological Society of North America.

Birdwell, who is also acting director of the radiology residency program at Stanford, tells WebMD "that was one of the most striking findings of our study -- half of the tumors were in non-dense breasts." Birdwell says that the study debunked most of the mammography lore that she believed. "I thought that missed lesions look different, were usually calcifications or occurred in unusual locations. In our study none of those assumptions turned out to be true."

She and her colleagues amassed records from more than 1,000 consecutive cases of breast cancer detected through mammogram screenings. In about half of the cases, prior mammograms were available for comparison. A radiologist then examined the paired mammograms and determined that in almost 300 cases, evidence of cancer was visible on the first mammogram but had not been identified. An expert panel of five radiologists, who were blinded to the results of the second mammogram, were asked to review the initial films. "A majority of the five identified 115 cancers in 110 women and recommended recall imaging," Birdwell says. She then studied the characteristics of these "missed" cancers.

"Most of them weren't calcifications. They were masses," she says. Eighty-two of the 115 were invasive cancers and almost half were in the upper outer quadrant of the breast, a "very common location," she says.

Birdwell offers several theories to explain the missed diagnoses, including a very simple one: the mammographers were too distracted by other tasks to concentrate on the films under review. She says that at most busy breast centers, films are reviewed in rooms that aren't dark enough and that are too accessible to distractions from co-workers. "I've only ever seen one ideal screening room. ... It was down a hall, away from the action, and completely dark. I don't even think there was a phone. I was envious."

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