UCSF: A new UC San Francisco-led study shows that women with “dense breasts” are at increased risk for breast cancer compared with women with a family history of the disease, their own history of benign lesions, or a first full-term pregnancy over age 30. The findings were published Thursday in the journal JAMA Oncology. Led by Natalie Engmann, a Ph.D. candidate in UCSF’s Department of Epidemiology and Biostatistics, and Dr. Karla Kerlikowske, the researchers believe their work is the first large-scale study to measure the development of breast cancer according to the degree of breast density.
About 40 percent of women in the U.S. over age 40 have dense breast
tissue, which makes it harder to identify cancer cells on a mammogram.
That’s because the breast tissue appears dense on a mammogram compared
with fat, which appears nondense.
As a result, 28 states — including California — have passed laws
requiring health facilities to notify women when they have dense
breasts. Proponents of the law say women can then decide if they want to
take further action and undergo other imaging techniques, such as an
ultrasound or MRI.
But critics say the laws cause women increased anxiety and cost
because there is no consensus if the routine supplemental screening is
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The UCSF-led study evaluated the risk factors of more than 200,000
women ages 40 to 74. About 18,000 of the participants had different
stages of breast cancer, while the rest did not.
The researchers found that breast density was the most prevalent risk
factor for the disease, and that 39.3 percent of breast cancers in
premenopausal women and 26.2 percent in postmenopausal women might have
been prevented if all women with higher breast density had been shifted
to a lower density category.
The researchers also found that women with a high body mass index
have lower breast density, though Engmann said age is also a strong
determinant of breast density.
Dense breasts are more common in younger women, said Engmann, and
most women experience a sharp decline during menopause that continues in
the postmenopausal period.
However, she noted that postmenopausal estrogen and progestin therapy can reverse the decline of breast density with age.
Tamoxifen, an estrogen hormone blocker, is the only treatment known
to substantially reduce breast density, and thus the risk of breast
cancer. But because the drug can have serious side effects, it is
usually recommended only for women at high risk of breast cancer, with
guidance from their physician.
“Our study highlights the need for new interventions to reduce breast density for women at average risk,” Engmann said.
At the Fremont-based Cancer Prevention Institute of California,
cancer epidemiologist Dr. Ingrid Oakley-Girvan was intrigued by the UCSF
She called the study “exciting because it provides further evidence
we should continue investigating ways to reduce the risk of breast
For example, along with some of her colleagues, Oakley-Girvan
recently submitted a proposal to the U.S. Department of Defense to
evaluate whether a nutritional soup product reduces inflammation in the
breasts of women with early disease.
“Perhaps we should also consider expanding that work to include women with dense breasts,” noted Oakley-Girvan.
At UCSF, Engmann said that even though one link between dense breasts
and breast cancer suggests that carrying extra pounds may protect women
against the disease, since overweight and obese women are more likely
to have fatty breasts, the study reinforced previous research that has
established a link between high body mass index and increased breast
cancer risk in postmenopausal women.
The researchers said that almost 23 percent of breast cancers in this
group could have been averted if obese and overweight women attained a
body mass index of less than 25, the equivalent of 155 pounds for a
woman who is 5 feet 6 inches.
By comparison, the study found that factors commonly associated with
breast cancer risk — a history of benign breast biopsy, a first-degree
family history of breast cancer, and deferring childbirth until after 30
— each accounted for less than 10 percent of cases in the population.
The study was supported by a National Cancer Institute-funded program.