Most breast cancers among premenopausal and postmenopausal women could be attributed to high breast density and BMI, according to results of a case–control study.
These data suggest that interventions to address these factors could reduce breast cancer risk, researchers wrote.
“These risk factors represent clinically available data that can and should be used to stratify risk, using established risk models that include breast density to promote risk-based screening and targeted prevention efforts,” Natalie J. Engmann, MSc, PhD student in the department of epidemiology and biostatistics at UCSF, and colleagues wrote.
Many women diagnosed with breast cancer have no established clinical breast cancer risk factors or were not considered to be high risk. However, easily assessed risk factors that explain a substantial proportion of incidence breast cancers could be used to stratify risk for targeted screening and primary prevention, as well as to improve public health interventions.
To estimate the proportion of breast cancers attributable to risk factors commonly reported in clinical practice, the researchers used the Breast Cancer Surveillance Consortium (BCSC) registry to evaluate data from 18,437 women with invasive breast cancer or ductal carcinoma in situ matched based on age, year of risk factor assessment and BCSC registry to 184,309 women without breast cancer. This included 58,146 premenopausal women (mean age, 46.3 years) and 144,600 postmenopausal women (mean age, 61.7 years), all of whom were undergoing mammography at community-based BCSC breast imaging facilities.
Researchers prospectively collected risk factor data — which included Breast Imaging Reporting and Data Systems breast density, first-degree family history of breast cancer, BMI, history of benign breast biopsy, and nulliparity or age at first birth — from January 1996 to October 2012.
Among all patients, 4,747 premenopausal (89.8%) and 12,502 postmenopausal (95.1%) women had at least one breast cancer risk factor, compared with 43,111 premenopausal controls (81.6%) and 120,227 postmenopausal controls (91.5%).
In addition, 56.5% of premenopausal women with breast cancer had two or more risk factors compared with 42.2% of premenopausal controls. More postmenopausal women with breast cancer had two or more risk factors (66.2%) compared with postmenopausal controls (53.7%).
Increased risk for breast cancer occurred among women with a first-degree family history of breast cancer, history of benign breast biopsy, dense breasts, and nulliparity or age older than 30 years at first birth.
Overweight and obese postmenopausal women were at an increased risk for breast cancer. Risk was 1.23 times higher in overweight women, 1.39 times higher in women with class I obesity, and 1.54 times higher in women with class II or III obesity. However, obesity was not associated with breast cancer risk in premenopausal women.
The largest population-attributable risk proportion of breast cancer was breast density in both groups of women. In total, 39.3% (95% CI, 36.6-42) of premenopausal breast cancers and 26.2% (95% CI, 24.4-28) of postmenopausal breast cancers could have been averted if all women with heterogeneously or extremely dense breasts shifted to scattered fibroglandular breast density.
For postmenopausal women, 22.8% (95% CI, 18.3-27.3) of breast cancers could potentially be averted if all overweight and obese women had a BMI less than 25.
“Future research should assess whether population-attributable risk proportion estimates differ by molecular subtypes of breast cancer, where the magnitude and direction of risk factors may differ,” the researchers wrote. – by Melinda Stevens
: The researchers report no relevant financial disclosures.