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Breast density was associated with an increased risk of invasive breast cancer among women ages 65 and older, according to results from a prospective cohort study.

Regardless of body mass index (BMI), extreme or heterogeneous breast density was associated with increased risk of breast cancer compared with scattered fibroglandular breast density in women ages 65 to 74 (HR 1.39, 95% CI 1.28-1.50) and those ages 75 and older (HR 1.23, 95% CI 1.10-1.37), reported Dejana Braithwaite, PhD, MSc, of the University of Florida Health Cancer Center in Gainesville, and colleagues.

"Although breast density is important in risk assessment and could be evaluated in older women, some risk prediction models do not provide risk estimates for women aged 75 or older," the authors wrote in . "Given that greater breast density as categorized by the BI-RADS [Breast Imaging Reporting and Data System] remains a factor associated with breast cancer even in older women, information about breast density together with life expectancy may benefit clinical decision-making regarding whether screening after 75 years of age should be continued."

Women in the U.S. who live to the age of 75 have an average life expectancy of another 12 to 14 years, noted Catherine Tuite, MD, of ChristianaCare Helen F. Graham Cancer Center and Research Institute in Newark, Delaware, in a .

"The incidence of breast cancer increases with age, and given that the data support at least a modest association between breast cancer risk and breast density in older women, 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," she wrote.

While current breast density notification laws suggest that supplemental screening is beneficial for women with dense breasts, this has not been established for older women, Braithwaite and team noted.

For their study, they examined the association between breast density and invasive breast cancer among older women, as well as if BMI modified these associations.

The study used data obtained from the Breast Cancer Surveillance Consortium for U.S. women ages 65 and older who underwent screening mammography from January 1996 through December 2012. A total of 221,714 screening mammograms from 193,787 women (38% of whom were ≥75 years old) were included in the study. Of the mammograms, a majority were from women ages 65 to 74 (64.6%) and white women (81.4%).

Breast density was classified according to the American College of Radiology's BI-RADS categories: almost entirely fat (BI-RADS a), scattered fibroglandular densities (BI-RADS b), heterogeneously dense (BI-RADS c), and extremely dense (BI-RADS d).

Among women ages 65 to 74, 16.5% were in the BI-RADS a group, 51.4% were in the BI-RADS b group, and 32.1% were in the BI-RADS c or d group. Among women ages 75 and older, 17.5% were BI-RADS a, 52.0% were BI-RADS b, and 30.5% were BI-RADS c or d.

During a mean follow-up of 6.3 years, 5,069 invasive cancers were diagnosed in the study population.

For women ages 65 to 74, the 5-year cumulative incidence of invasive breast cancer increased in association with increasing breast density:

• 11.3 per 1,000 women (95% CI 10.4-12.5) in the BI-RADS a group
• 17.2 per 1,000 women (95% CI 16.1-17.9) in the BI-RADS b group
• 23.7 per 1,000 women (95% CI 22.4-25.3) in the BI-RADS c or d groups

The same was true for women ages 75 and older:

• 13.5 per 1,000 women (95% CI 11.6-15.5) in the BI-RADS a group
• 18.4 per 1,000 women (95% CI 17.0-19.5) in the BI-RADS b group
• 22.5 per 1,000 women (95% CI 20.2-24.2) in the BI-RADS c or d groups

The authors also observed that women ages 65 to 74 with almost entirely fatty breasts had a reduced risk of invasive breast cancer compared with women with scattered fibroglandular breast density, regardless of BMI (HR 0.66, 95% CI 0.58-0.75; BMI ≥25: HR 0.71, 95% CI 0.61-0.81; BMI <25: HR 0.53, 95% CI 0.40-0.72).

This was also the case for women ages 75 and older (HR 0.73, 95% CI 0.62-0.86) and for those with a BMI of ≥25 (HR 0.70, 95% CI 0.57-0.86), but not for those with a BMI <25 (HR 0.82, 95% CI 0.62-1.09).

There was no significant interaction between BMI and breast density among women ages 65 to 74 (likelihood ratio test 2.67, df 2, P=0.26) and those 75 and older (likelihood ratio test 2.06, df 2, P=0.36).

"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," Braithwaite and colleagues concluded.

"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," noted Tuite.

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