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Breast density is a known risk factor for developing breast cancer, but that well-accepted research finding is derived from studies conducted in women under age 75. That makes sense because breast density declines with age, but cancer epidemiologist Dejana Braithwaite of the University of Florida’s Cancer Control and Population Sciences Program wondered about older women: How much does density drop, and how much might it matter?

In an analysis of more than 220,000 mammograms published Thursday in JAMA Oncology, her team reports that density — and the risk of breast cancer — doesn’t disappear.

Braithwaite talked with STAT about that research and her hope to learn more about cancer in older women. This interview has been condensed and lightly edited for clarity.

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What were you hoping to learn?

While screening for women up to 75 is generally accepted to be appropriate, what’s less clear is what happens after women reach age 75 and whether screening still makes sense. What we really want to do is generate the evidence to inform personalized screening strategies. For some women it may make sense to continue screening beyond age 75, beyond what’s recommended by the guidelines if they’re in good health and maybe have some risk factors like breast density. But for some women who may have some health issues, they may not benefit from screening.

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Dejana Braithaiwte
Cancer epidemiologist Dejana Braithwaite Courtesy University of Florida

What’s the connection between breast density and cancer?

One of the really common risk factors for breast cancer is breast density, and that’s a measure of the amount of fibers or glandular tissue — dense tissue —compared with fatty tissue. More density has been associated with increased risk of invasive breast cancer.

And for older women?

Ours is one of the first studies to really look at older women, particularly women aged 75 and older. Even though the prevalence of density decreases with age, about half of women age 40 to 64 have dense breasts, and we found that by the time women get into their 60s and 70s, about 30% to 32% still have dense breasts. And we found that their breast density is associated with increased risk of invasive breast cancer in both age groups of women that we studied: 65 to 74, and 75 and older.

Was that unexpected?

It is surprising that 30% of these women still have dense breasts — that’s maybe a little bit higher than what we expected. After menopause, it goes down, but 30% is still a considerable number. Given the associations we have observed in younger women that density does lead to an increased risk of breast cancer, that finding is not surprising. It’s biologically plausible.

How do you imagine your work might affect the care women get or decisions they make about continuing to get screening mammograms?

We think that breast density should be included in prediction models that are aimed at estimating breast cancer risk, and to consider that in conjunction with life expectancy to make informed decisions about potential benefits versus harms of continued screening. We’re currently developing an intervention that’s aimed at women and primary care physicians to provide a personalized risk assessment tool to help guide conversations about screening after age 75.

When does screening still make sense?

Between 75 and 80, some women who have a good life expectancy of at least 10 years may still benefit from continuing mammography. It’s really more that after age 80, fewer women would be likely to live another 10 years to really benefit. But there’s a general consensus that for any type of cancer screening, if you have a 10-year life expectancy, then there’s a high chance that you will benefit from cancer screening.

This year, screening recommendations for lung and colorectal cancer have started at younger ages. Your work suggests extending it at the other end of life.

Yes, the questions are kind of similar, you know, when to start and then when to discontinue and how often to screen. In addition to breast cancer screening, I do also have a grant that’s focusing on lung cancer screening. And the guiding principle of our work is really to develop the evidence that can be translated into interventions to facilitate risk-based screening. What we mean by that is really individualizing cancer screening based on patient characteristics and, overall, how to maximize the benefits and minimize the harms.

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