The findings, based on an analysis of Breast Cancer Surveillance Consortium data from Jan. 1, 1996, to Dec. 31, 2012, have potential implications for screening mammography decisions in older women – particularly those aged 75 years and older, for whom screening guidance is limited by a paucity of data, Dejana Braithwaite, PhD, of the University of Florida Health Cancer Center, Gainesville, and colleagues reported in JAMA Network Open.
The investigators analyzed 221,714 screening mammograms from 193,787 women aged 65 and older in the United States. About 65% of the mammograms were from women aged 65-74 years and about 35% were from women aged 75 years and older, who comprised 38% of the study population.
During a mean follow-up of 6.3 years, 5,069 invasive breast cancers were diagnosed, the authors noted.
The 5-year cumulative incidence of invasive breast cancer increased in tandem with increasing breast density among those aged 65-74 years and among those aged 75 and older: The cumulative incidence per 1,000 women aged 65-74 years was 11.3 for those with almost entirely fatty breasts, 17.2 for those with scattered fibroglandular densities, and 23.7 for those with extremely or heterogeneously dense breasts. The cumulative incidence rates for those aged 75 years and older were 13.5, 18.4, and 22.5 per 1,000 women, respectively, they found.
Extreme or heterogeneous breast density was associated with increased risk of breast cancer, compared with scattered fibroglandular breast density, in both age categories (hazard ratios, 1.39 and 1.23 for those aged 65-74 years and 75 years and older, respectively), whereas the risk of invasive breast cancer was about 30% lower among women with almost entirely fatty breasts, compared with women with scattered fibroglandular breast density (HRs, 0.66 and 0.73 for the 65-74 and 75-plus age groups, respectively).
The associations between breast density and breast cancer were statistically significant after adjustment for body mass index (BMI) and other risk factors.
However, no significant differences were seen between breast density and breast cancer risk based on BMI, noted the authors, who investigated this potential association as part of their effort to identify subpopulations of older women who might benefit from screening, “especially because the U.S. Preventive Service Task Force guidelines state that the current evidence is considered insufficient to recommend routine breast cancer screening for women aged 75 years or older,” they wrote.
Further, although breast density is important in risk assessment and could be evaluated in older women, some risk prediction models exclude women aged 75 or older in risk assessments, they noted, adding that this is concerning given “the aging of the population in the U.S. and worldwide.”
“The positive associations found in this study between breast density and breast cancer among women aged 75 years or older suggest that breast density and life expectancy should be considered together when discussing the potential benefits and harms of continued screening mammography in this population,” they concluded.
The new findings supplement those from prior studies and highlight “the intersection of ... two subjects that have garnered considerable lay public, healthy policy, and academic interest” in recent years: screening mammography in older women and the risk of breast cancer caused by breast density in older women, Catherine M. Tuite, MD, of ChristianaCare Helen F. Graham Cancer Center and Research Institute, Newark, Del., wrote in a commentary published with the study.
“Although there is a linear association between age and mammographic density, age is not a perfect surrogate for the latter, and there are meaningful numbers of older women with mammographically dense breast tissue,” she said, noting that a 75-year-old woman in the United States has a life expectancy of 12-14 additional years, and that “continuation of screening mammography in healthy women aged 75 years or older may offer a substantial opportunity to avoid morbidity and mortality from breast cancer in this age group.”
However, overdiagnosis also remains a concern, she said.
“Breast density and age are only a few of the many factors currently under investigation in the drive toward risk-based or personalized breast cancer screening,” she wrote. “We must remain cautious in the application of restrictive screening for women of any age with supposedly lower than average risk ... ultimately, the decision of when to stop screening is personal, and each woman deserves the agency to weigh her own wishes, values, and life experiences with an accurate and unbiased discussion of risks and benefits of screening mammography in making that decision.”
This study was supported by grants from the National Cancer Institute and the Breast Cancer Surveillance Consortium. Cancer and vital status data collection was supported in part by several state public health departments and cancer registries. Dr. Advani and Dr. Tuite each reported having no disclosures.