The researchers found that women who've had breast biopsies that turned out to be benign have an 80% greater risk of getting the disease in their 40s; women on oral contraceptives have a 30% increased risk; women who have never given birth have a 25% greater risk; and women who had their first child after age 30 have a 20% increased risk.
In an editorial accompanying the two studies, Brawley said the findings about dense breasts create "several conundrums," not least that their mammograms are difficult to interpret. If breast density becomes a factor that drives how often women should be screened, he wrote, future guidelines may include the recommendation that all women get a baseline mammogram at age 40.
Dr. Patricia Ganz, a breast cancer specialist at UCLA, said the studies would help in the development of "user-friendly ways that a primary-care physician can start that conversation" about a woman's breast cancer risk and what steps she can take to address it. Ganz said the findings underscored the central importance of taking a family history — and of updating it as a woman (and her mother and sisters) age.
But Ganz too said the key risk factor of breast density needed better definition if it was to be a helpful guidepost to women and their doctors. Radiologists, who review mammograms, and primary-care doctors have no established standards or software that defines and grades breast density, she said, so sending all 40-year-old women to have their breast density assessed would be premature.
"It's not really ready for prime time," she said.