The combination of high breast density and high body mass index (BMI) increase breast cancer risk, with a stronger association found among postmenopausal women, according to research published December 23 in JAMA Network Open.
Both factors should be incorporated into risk classification in population-based screening, wrote a team led by Thi Xuan Mai Tran, PhD, from Hanyang University in South Korea.
"Women with overweight or obesity and dense breast tissue might benefit from tailored early screening strategies to detect breast cancer," Tran and colleagues wrote.
Dense breast tissue and obesity are known to individually be strong risk factors for breast cancer. However, there is controversy around the magnitude of the combined associations of these two factors with breast cancer risk, especially when it comes to menopausal status.
Tran's team sought to investigate the interaction for breast cancer risk between breast density, BMI, and menopausal status. The group evaluated data from 3.2 million premenopausal women with an average age of 45 years and 4.4 million postmenopausal women with an average age of 60 years from the Korean National Cancer Screening Program. Out of these, 34,466 cases of breast cancer were identified among the premenopausal group and 30,816 among the postmenopausal group.
The investigators found that increased breast density was associated with a higher risk of breast cancer in both premenopausal and postmenopausal women across the BMI categories.
Among premenopausal women, those in the BI-RADS 4 category had double the risk of breast cancer without taking BMI into account compared with those who were underweight and in the BI-RADS 1 category.
However, Tran's team also found that when breast density and BMI combined with breast cancer risk were considered, high breast density and high BMI had a "significant" positive interaction for both premenopausal and postmenopausal women -- especially the latter.
The researchers said this study's findings are generalizable to East Asian women, who tend to have a higher breast density than Western women. They added that their results could also be applied to Western populations of women with increasing obesity.
"Our findings suggest that breast density notification should be provided not as a stand-alone risk factor but as an adjunct factor with BMI for risk stratification in population-based mammographic screening settings for public health significance," the authors noted.
In an accompanying commentary, Claudia Mello-Thoms, PhD, of the University of Iowa in Iowa City called the team's results "surprising," writing that the study may have implications for breast cancer risk models, including ones used in the U.S.
"In light of the findings by Tran et al that the interaction between BMI and breast density is additive, it suggests that perhaps these models are in fact underestimating breast cancer risk by not taking into account both factors," she wrote.