Many women underestimate breast density as a risk factor for breast cancer, study shows

By Janelle Chavez, CNN

Dense breast tissue has been associated with up to a four times higher risk of breast cancer. However, a new study suggests few women view breast density as a significant risk factor.

The study, published in JAMA Network Open, surveyed 1,858 women ages 40 to 76 years from 2019 to 2020 who reported having recently undergone mammography, had no history of breast cancer and had heard of breast density.

Women were asked to compare the risk of breast density to five other breast cancer risk factors: having a first-degree relative with breast cancer, being overweight or obese, drinking more than one alcoholic beverage per day, never having children and having a prior breast biopsy.

“When compared to other known and perhaps more well-known breast cancer risks, women did not perceive breast density as significant of a risk,” said Laura Beidler, an author of the study and researcher at the Dartmouth Institute for Health Policy and Clinical Practice.

For example, the authors report that dense breast tissue is associated with a 1.2 to four times higher risk of breast cancer compared with a two times higher risk associated with having a first-degree relative with breast cancer — but 93% of women said breast density was a lesser risk.

Dense breasts tissue refers to breasts that are composed of more glandular and fibrous tissue than fatty tissue. It is a normal and common finding present in about half of women undergoing mammograms.

The researchers also interviewed 61 participants who reported being notified of their breast density and asked what they thought contributes to breast cancer and how they could reduce their risk. While most women correctly noted that breast density could mask tumors on mammograms, few women felt that breast density could be a risk factor for breast cancer.

Roughly one-third of women thought there was nothing they could do to reduce their breast cancer risk, although there are several ways to reduce risk, including maintaining a healthy, active lifestyle and minimizing alcohol consumption.

Dense breast tissue

Breast density changes over a woman’s lifetime, and is generally higher in women who are younger, have a lower body weight, are pregnant or breastfeeding, or are taking hormone replacement therapy.

The level of breast cancer risk increases with the degree of breast density; however, experts aren’t certain why this is true.

“One hypothesis has been that women who have more dense breast tissue also have higher, greater levels of estrogen, circulating estrogen, which contributes to both the breast density and to the risk of developing breast cancer,” said Dr. Harold Burstein, a breast oncologist at the Dana-Farber Cancer Institute who was not involved in the study. “Another hypothesis is that there’s something about the tissue itself, making it more dense, that somehow predisposes to the development of breast cancer. We don’t really know which one explains the observation.”

Thirty-eight states currently mandate that women receive written notification about their breast density and its potential breast cancer risk following mammography; however, studies have shown that many women find this information confusing.

“Even though women are notified usually in writing when they get a report after a mammogram that says, ‘You have increased breast density,’ it’s kind of just tucked in there at the bottom of the report. I’m not sure that anyone is explaining to them, certainly in person or verbally, what that means,” said Dr. Ruth Oratz, a breast oncologist at NYU Langone’s Perlmutter Cancer Center who was not involved in the study.

“I think what we’ve learned from this study is that we have to do a better job of educating not only the general public of women, but the general public of health care providers who are doing the primary care, who are ordering those screening mammograms,” she added.

‘Screening is not a one size fits all recommendation’

Current screening guidelines recommend women of average risk of breast cancer undergo breast cancer screening every one to two years between ages 50 to 74 with the option of beginning at age 40.

Because women with dense breast tissue are considered to have higher than average cancer risks, the authors of the study suggest women with high breast density may benefit from supplemental screening like breast MRI or breast ultrasound, which may detect cancers that are missed on mammograms. Currently, coverage of supplemental screening after the initial mammogram varies, depending on the state and insurance policy.

The authors warn that “supplemental screening not only can lead to increased rates of cancer detection but also may result in more false-positive results and recall appointments.” They say clinicians should use risk assessment tools when discussing tradeoffs associated with supplemental screening.

“Usually, it’s a discussion between the patient, the clinical team, and the radiologist. And it’ll be affected by prior history, by whether there’s anything else of concern on the mammogram, by the patient’s family history. So those are the kinds of things we discuss frequently with patients who are in such situations,” Burstein said.

Breast cancer screening recommendations differ between medical organizations, and experts say women at higher risk due to breast density should discuss with their doctor what screening method and frequency are most appropriate.

“I think it’s really, really important that everyone understands — and this is the doctors, the nurses, the women themselves — that screening is not a one size fits all recommendation. We cannot just make one general recommendation to the entire population because individual women have different levels of risks of developing breast cancer,” Oratz said.

Decreasing your breast cancer risk

For the nearly one-third of women with dense breast tissue that reported there was nothing they could do to prevent breast cancer, experts say there are some steps you can take to reduce your risk.

“Maintaining an active, healthy lifestyle and minimizing alcohol consumption address several modifiable factors. Breastfeeding can decrease the risk. On the other hand, use of hormone replacement therapy increases breast cancer risk,” said Dr. Puneet Singh, a breast surgical oncologist at the MD Anderson Cancer Center who was not involved in the study.

The researchers add that there are approved medications, such as tamoxifen, that can be given for those at significantly increased risk that may reduce the chances of breast cancer by about half.

Finally, breast cancer doctors say that in addition to appropriate screening, knowing your risk factors and advocating for yourself can be powerful tools in preventing and detecting breast cancer.

“At any age, if any woman feels uncomfortable about something that’s going on in her breast, if she has discomfort, notices a change in the breast, bring that to the attention of your doctor and make sure it gets evaluated and don’t let somebody just brush you off,” Oratz said.

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