Of 13 possible risk factors, they found extremely dense breast tissue or a first-degree relative with breast cancer (parent, sibling or child) doubled the risk of breast cancer in women 40 to 49. Breast density is determined through by mammography.
About 13 percent of women in their 40s have extremely dense breast tissue and 9 percent have a first-degree relative with breast cancer.
Next, they performed a technique called collaborative modeling to estimate the harms and benefits of every-other-year mammography for these under-50, high-risk women.
Researchers put together four independent models to see if a doubling of risk changed the balance of harms and benefits.
All four models concluded that higher-risk women 40 to 49 who start every-other-year screenings at age 40 have the same benefit-harm ratio as average-risk women 50 to 74 who have mammograms every two years.
"Our models don't say what they [women] should do," Mandelblatt said. The conclusions will help inform women and professional organizations that formulate recommendations, the experts said.
The researchers found small differences in benefits between film mammography and the newer digital mammography. The digital forms had more false-positives.
In digital mammograms, the breast image is electronic and stored in the computer rather than on film.
The new research confirms some of what experts already know, said Judith Malmgren, an affiliate assistant professor of epidemiology at the University of Washington, in Seattle. "We already knew that women with a family history of breast cancer should start screening at age 40," she said.
The new data "shows the balance [of harms and benefits] more conclusively," she said.
However, modeling studies aren't real life, so they have limitations, she said.
The models took into account life years gained and breast cancer deaths averted, as well as potential harms, she
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