Aug. 26 (UPI) -- Older women with extremely dense breast tissue are up to 40% more likely to develop breast cancer than those "almost entirely fatty" breasts, an analysis published Thursday by JAMA Network Open found.
The risk for cancer was even higher among women with high-density breast tissue who were overweight or obese based on body mass index, the data showed.
Women with BMIs of 25 or above with extremely dense breast tissue had a two-fold higher risk for the disease compared to those with lower BMIs whose breasts were made up almost entirely of fatty tissue, the researchers said.
BMI is calculated by taking a person's weight in kilograms and dividing it by their height in meters, according to the Centers for Disease Control and Prevention.
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Women with BMIs above 25, but less than 30, are considered overweight, while those with BMIs above 30 are considered obese, the agency says.
"This study provides evidence that breast density remains an important risk factor in older women," study co-author Diana L. Miglioretti said in a press release.
"[It] should be included in risk prediction models that also consider life expectancy to help identify women who may benefit most from continued screening," said Miglioretti, a researcher at the University of California-Davis.
The tissue in breasts is composed of milk glands, milk ducts and supportive, or dense, breast tissue, as well as fatty tissue.
Tissue density is detected during mammogram screening, with non-dense breast tissue appearing dark and transparent and dense breast tissue registering as a solid-white area, according to the Mayo Clinic
About one in 10 women has extremely dense breast tissue, placing them at increased risk for breast cancer, while the breasts of another one in 10 women are composed almost entirely of fatty tissue, with the rest having majority dense or majority non-dense tissue, Mayo estimates.
Roughly half of all women who undergo mammograms have dense breasts, which makes spotting tumors more challenging and increases risk for developing breast cancer, according to Mayo.
For this study, Miglioretti and her colleagues analyzed more than 220,000 screening mammograms for nearly 200,000 women, all of whom were age 65 and older and 35% of whom were older than 75.
Just over 56% of the women in the study had BMIs of 25 or above, meaning they were overweight or obese.
Of the mammograms included in the analysis, 32% showed highly or extremely dense breast tissue, the researchers said.
However, about 64% of the women with BMIs of 25 or above had highly or extremely dense breast tissue on their mammograms, the data showed.
In women ages 65 to 74, those with high or extreme breast densities on mammogram screenings, regardless of BMI, had a 39% higher risk for breast cancer compared to women with less-dense breast tissue.
Women in this age group with dense breast tissue and BMIs of 25 or above also had a 39% higher risk for the disease compared to those with less dense breast tissue and lower BMIs.
The risk for breast cancer was 23% higher in women age 75 and older with high or extreme breast density and 29% higher in those who also had BMIs of 25 and higher.
The U.S. Preventive Services Task Force, an independent panel of national experts on disease prevention and evidence-based medicine, does not recommend for or against mammography screening for women age 75 or older, citing insufficient scientific evidence.
However, the 30% to 32% of older women with high breast density should consider talking to their doctors about whether having high breast density sufficiently increases their risk for breast cancer to warrant ongoing screening mammography, the researchers said.
"Our goal is to develop the evidence that helps personalize breast cancer screening for older women," study co-author Dejana Braithwaite said in a press release.
"Older women who are in good health and have dense breasts may consider a screening mammogram even as they age beyond the screening recommendations for average-risk women," said Braithwaite, director of population sciences at the University of Florida Health Cancer Center in Gainesville.
