More and more U.S. women are learning that they have dense breasts, a risk factor for breast cancer. But many don't know what that means, and the knowledge gap can create anxiety.
At least 38 states and the District of Columbia have adopted legislation requiring women to receive some type of breast density notification after a mammogram, and in 2019 the FDA proposed national expansion of breast density reporting by mammography facilities. However, despite receiving notifications, women living in states where notification is required do not necessarily have an increased understanding of the clinical implications of dense breasts, according to a study published in January by the Journal of General Internal Medicine.
“They weren't more likely to know that it increased their risk of breast cancer, and they also weren't more likely to know that it would be harder to find a cancer on a mammogram—two key things that we are concerned about with increased breast density,” said ACP Member Kelly Kyanko, MD, MHS, lead author of the study and assistant professor in the department of population health at New York University School of Medicine.
While women were generally more likely to be aware of their dense breasts if they lived in a state with a notification law, those with lower education levels were not. In most states, the dense-breast notifications in mammogram letters are written above most women's reading level, noted Dr. Kyanko, who is also a primary care physician at NYC Health + Hospitals/Bellevue in New York City.
“I think women, more than anything, are just confused when they get that letter, and they're a little concerned,” she said. “And they're coming to us to help interpret for them.”
Internists are constantly pressed for time during visits. But when patients ask them about breast density, a couple of quick talking points can help, said Joann Elmore, MD, MPH, the Rosaline and Arthur Gilbert Foundation Endowed Chair in Health Care Delivery Professor of Medicine at the David Geffen School of Medicine at the University of California, Los Angeles (UCLA).
Clearly explaining what breast density is and counseling patients about their breast cancer risk can help educate women and alleviate any anxiety, she said. “The most important thing is to explain to women that dense breast tissue is not abnormal and that almost half of women in the U.S. have it,” said Dr. Elmore.
Defining breast density
Over the past decade, breast density has gone from “an obscure medical term to break room conversation,” according to a review in the April 2014 Mayo Clinic Proceedings. In 2009, Connecticut became the first state to require such notification, following the advocacy efforts of Nancy Cappello, PhD, who was diagnosed with advanced breast cancer via physical exam just six weeks after her yearly mammogram reported normal results, potentially due in part to dense breast tissue.
These state laws have come from a true desire to help women understand the association of dense breast tissue with breast cancer, as well as the limitations of mammograms, said Nancy L. Keating, MD, MPH, FACP, professor of health care policy at Harvard Medical School in Boston and coauthor of a May 2019 JAMA viewpoint about the FDA's proposed federal notification requirements.
“However, the vast majority of women with dense breasts will not develop breast cancer, and these policies, which are not grounded in evidence, risk causing harm by increasing anxiety and confusion without providing clear recommendations about what women with dense breasts should do,” she said.
That's where internists can play a pivotal role, said Amy Tu Wang, MD, FACP, lead author of the review article. “I think the best thing we can do is to understand breast density and its implications so we can explain it to patients in a way that makes sense and empowers women, rather than focuses on things they can't control,” she said.
Breast density describes the amount of fibroglandular tissue compared to fatty tissue, and having more dense breast tissue can decrease the sensitivity of mammography, explained Dr. Wang. “Fatty tissue is more transparent on a mammogram, whereas fibroglandular tissue is white and hard to see through, potentially masking tumors,” she said.
Per the Breast Imaging Reporting and Data System (BI-RADS), there are four categories of breast tissue density: A, almost entirely fatty (less than 25% glandular tissue); B, scattered areas of fibroglandular density (about 25% to 50% glandular tissue); C, heterogeneously dense (about 51% to 75% glandular tissue); and D, extremely dense (more than 75% glandular tissue). Studies have found that the sensitivity of mammography decreases with increasing breast density, ranging from 88% and 82% for women with category A and B density, respectively, compared with 69% and 62% for women with category C and D density, respectively, according to the Mayo Clinic Proceedings review.
It is common for women to have dense breasts, defined as either heterogeneously or extremely dense (BI-RADS category C or D). Among women ages 40 to 74 years, about 43% have dense breasts, according to a study published in September 2014 by the Journal of the National Cancer Institute.
“I think it's also important for internists to communicate how common this is, that it affects nearly half of women,” said Dr. Wang, an associate clinical professor of medicine at the David Geffen School of Medicine at UCLA. An easy way to remember that is “1:4:4:1,” she said: Population-based data show that overall, about one in 10 women have category A breast density, four out of 10 have B, four out of 10 have C, and nearly one out of 10 have D, with categories C and D considered increased breast density.
It is especially common for younger women to have dense breasts, and density decreases with age, said Dr. Wang. In one study of 7,000 women, about three-quarters of those in their 40s had dense breasts, compared to about one-third of those in their 70s, according to results published in the March 2012 American Journal of Roentgenology.
“Breast tissue is more functional and active in younger women and changes composition with menopause, usually becoming more fatty over time,” said Dr. Wang, who is also associate program director of the internal medicine residency and medical director for employee health at Harbor-UCLA Medical Center in Torrance, Calif.
Putting risk into perspective
Even after accounting for its masking effect on mammography, dense breast tissue is itself a risk factor for breast cancer, although the reasons why are not fully understood, said Dr. Wang. The increased risk varies by density category, but talking to patients about their breast cancer risk doesn't have to be complicated, she said.
For women in their 40s with category C breast density, the risk is only slightly increased. They have a relative risk of 1.62 compared to women with category B breast density, according to a systematic review and meta-analysis published in May 2012 by Annals of Internal Medicine. This increased risk is comparable to having an aunt who was diagnosed with breast cancer, said Dr. Elmore, who coauthored a Beyond the Guidelines article on the subject, published by Annals in October 2018. On the other hand, women with extremely dense breasts (category D) are at slightly more than double the risk compared to those with category B breast density, which is similar to having a first-degree relative with breast cancer, she said.
Rather than describing relative risk to patients, explaining their absolute risk of breast cancer may help provide a more meaningful impression of the impact of dense breasts, said Dr. Elmore. For example, out of 1,000 women with category C breast density, 20 will be diagnosed with breast cancer over the next 10 years, compared to 13 women with category B density, she said. Of 1,000 women with category C density who also have the BRCA1 mutation, 227 would be diagnosed with breast cancer over the next decade, Dr. Elmore noted.
“The number of women that end up getting breast cancer looks so small in 10 years,” she said. “I think that that is important to lay the ground because everyone has a heightened fear of breast cancer, and they feel that it's more common than it is.”
No matter which way internists explain risk, it's important to emphasize that women with dense breasts are not at increased risk for dying of breast cancer, Dr. Elmore added. “There has been no association of increased breast density and increased risk of dying of breast cancer,” she said, which can be reassuring for patients to hear.
In addition, among women who do get breast cancer, the vast majority will do very well, added Dr. Keating, who is also professor of medicine and a general internist at Brigham and Women's Hospital in Boston. “It is important to help women put these risks in perspective. … Compared with other serious conditions, a woman's risk of dying of breast cancer in her lifetime is about one in 39, versus a one in 22 risk of dying of lung cancer and one in three risk of dying of heart disease,” she said.
To that point, Dr. Kyanko added that it's important to place breast cancer risk in the context of a woman's overall health priorities. “One of the most important things we do as internists is helping patients prioritize,” she said. “So if a woman is smoking or has poorly controlled diabetes or has other issues, addressing those issues might be more likely to improve her survival and quality of life as compared to her breast cancer risk.”
Women can't change their breast density. However, internists should help them understand that increased breast density is just one of many potential risk factors for breast cancer, Dr. Kyanko said. “It's important to consider a woman's overall or global risk for breast cancer” by using risk assessment tools that account for family history and other risk factors, she said.
One of the most widely used online risk assessment tools is the National Cancer Institute's Breast Cancer Risk Assessment Tool, although it does not account for dense breast tissue. An online tool that does factor in a woman's BI-RADS breast density is the Breast Cancer Surveillance Consortium Risk Calculator.
After explaining breast density and breast cancer risk, it's time to come up with an action plan for patients with dense breasts.
First, internists can focus on lifestyle risk factors that are within a woman's control by encouraging patients to quit smoking, exercise regularly, eat nutritious foods, limit alcohol intake, and maintain a healthy weight, Dr. Wang said. Women at higher risk could also discuss use of oral contraceptives and hormone replacement therapy and potential alternatives, as these may be associated with a slight increase in breast cancer risk, she said.
Internists can also consider encouraging women with dense breasts to be aware of any changes in their breasts, Dr. Wang said. “We're not recommending women to do breast self-exams anymore, but I think knowing how your breasts feel and being aware of any changes is key,” she said.
At this point, women with dense breasts may ask whether they need additional screening for breast cancer beyond getting a screening mammogram, but there isn't a clear-cut answer. In its 2016 recommendation statement, the U.S. Preventive Services Task Force concluded that the evidence was insufficient to assess the benefits and harms of adjunctive breast cancer screening using breast ultrasonography, MRI, digital breast tomosynthesis, or other methods in women identified to have dense breasts on an otherwise negative screening mammogram.
Dr. Wang noted that most mammograms in the U.S. are now done digitally, which is more accurate than film mammography for screening dense breasts for cancer. From a radiology standpoint, most mammogram reports suggest routine mammography in a year compared to biennially for patients who have dense breasts, she noted. “I think that's reasonable, depending on overall risk.”
While Dr. Elmore agreed that annual screening could be considered, she noted that the lifetime benefit of annual versus biennial screening among women in their 50s with no other risk factors except density is smaller than what many women think; the number of breast cancer-related deaths averted is just two per 1,000 women, while the harms, such as false-positive results, are almost twofold greater, she said.
As for supplemental screening modalities, the evidence suggests that digital breast tomosynthesis (3D mammogram) may produce fewer false-positive findings but produces up to twice the amount of radiation as a regular mammogram, Dr. Wang said. “It's becoming more widely available, but it's definitely not everywhere, and it does have that downside of exposure to more radiation,” she said.
With regard to MRI and ultrasonography, experts agreed that there is no evidence that the benefits of screening (i.e., early detection) outweigh the potential harms, which include false positives, overtreatment, overdiagnosis, and higher costs (especially with MRI). While the American College of Radiology's 2017 Appropriateness Criteria state that adding handheld or automated breast ultrasound to mammography can be considered in women with dense breasts to improve the cancer detection rate, the group also acknowledges that this substantially increases the false-positive rate.
Ultimately, these additional tests have not been shown to decrease breast cancer mortality, said Dr. Elmore. “There's no data showing that supplemental ultrasound or MRI will save lives for the average-risk woman who just has a class C or a class D density, so I don't recommend them,” she said. “But if someone wants to join a clinical study looking at these, I would encourage them.”
For women who are found to be at higher-than-average risk for developing breast cancer, internists can consider referral to a high-risk breast clinic, which can then provide genetic counseling, additional imaging, and/or risk-reduction medications as needed, said Dr. Wang. “I think the internist's job is to identify who is at higher risk and should be referred,” she said. “And it's not everybody who has increased breast density.”