Understanding Breast Density

For many years, all women over 40 were encouraged to receive annual mammograms. But over the last decade, this recommendation has been modified with different expert groups and medical organizations generating guidelines that differ in the age of initiation and cessation of mammography as well as the intervals of screening. Many now recommend that the harms of mammography—false positive results and biopsies—be discussed with patients and that patients’ personal risks as well as their values and preferences be taken into account.

The latest complication to breast cancer screening is breast density. Researchers and radiologists have long observed that breasts fall on a spectrum of breast density, from those composed largely of fatty tissue to those with a greater share of dense, fibroglandular tissue. National estimates find that more than 40 percent of screened women between ages 40 and 74 years, or over 27 million American women, can have mammograms that show dense breasts, as classified by radiologists.

As Parisa Tehranifar, assistant professor of Epidemiology, explains: “Breast density is one of the strongest independent risk factors for breast cancer. And large amount of dense breast tissue also interfere with detection, making it harder for mammograms to pick up tumors.”

Breast Density 101 for Patients: Is It Working?

As a result of nationwide patient advocacy, breast density has gained greater public understanding. Twenty-seven states now have breast density notification laws on the books –if a woman is found to have dense breasts on her mammogram, she will be notified of her density results as part of her mammogram report. In New York State, this information will also include text informing her that having dense breasts may be associated with the higher breast cancer risk and the possible higher likelihood of missed tumors on mammograms.

How well do patients understand these notifications? Are they following up with their doctors about their risk for breast cancer and potentially more intense screenings? Those are some of the questions Tehranifar is seeking to address in a new $2.78 million study funded by the National Institutes of Health/National Institute on Minority Health and Health Disparities.

Working with the Avon Foundation Breast Imaging Center here in Washington Heights, her study will follow 1,000 women for a year after their mammograms, gauging what they know about breast density, how they feel about their screenings, how well they understand their results, and if they are accessing any additional medical services as a result of their mammogram reports.

“I’m particularly interested in learning about any differences across racial, ethnic, or socioeconomic groups,” says Tehranifar. “We need to know how women are responding to the information—if it is being used differently depending on the education level, health literacy, access to coverage, or income. If the breast density notification is to achieve its intended purpose of improving women’s awareness of their risk and help with a more informed screening plan, we need to ensure everyone, no matter their resources, can reap these benefits. Disparities can take a while to develop, but we may be able to predict and possibly prevent them from developing in screening and early detection.”

Can Breast Density Help Improve Risk Models?

As she works to better understand patient comprehension of breast density, Tehranifar also sees an opportunity for breast density to be added into existing models that predict risk of breast cancer. A number of these risk models are used in clinical settings and some are freely available online. The vast majority of current risk models such as the well-known Breast Cancer Risk Assessment or Gail Model currently do not include breast density in their standard form.

With a grant from the National Cancer Institute, Tehranifar and her colleagues will tap into a cohort of patients from the Sister Study, a ten-year prospective study of more than 50,000 women with sisters who have had breast cancer. The Sisters Study already has a wealth of data on their participants: epidemiological data, risk factor data, clinical data, genetic and epigenetic data, as well as biospecimens—but so far there is no mammagraphic data. To fill this gap, Tehranifar and her colleagues will collect repeated mammograms for the Sisters Study participants to determine individual women’s changes in breast density over time and whether these trajectories can improve breast cancer risk assessment.

Tehranifar’s two studies explore breast density from different perspectives, and there are dozens of other ongoing studies around the world on the issue. “There’s still so much we don’t know about how breast density affects breast cancer development and how we can reduce breast density in ways that are safe, feasible and map to future breast cancer risk,” she says. “Yet there’s a lot of hope for its potential in the broader effort to reduce breast cancer burden.”