The Masking Effect: Dense Breasts and Women’s Health

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By Matt Skoufalos

For years, women’s health care advocates have pushed legislators at every level of government to pass breast density inform laws: regulations requiring providers to notify their patients about whether they have dense breast tissue as a component of their mammogram reports. Their efforts led to such laws being adopted in nearly 40 U.S. states, and finally, in February 2019, to a breast density inform bill being signed into federal law with the latest Congressional appropriations bill. The new federal law mandates that the U.S. Food and Drug Administration (FDA) develop standardized language for mammography reports that includes a qualitative assessment of patients’ breast densities, information about the difficulty in detecting cancer in dense breast tissue via traditional mammography, and a reminder that patients should consult their doctors if they have questions on the subject.

To understand why such information makes a significant difference in women’s health, how it supports the early detection of breast cancers that could otherwise be hidden, and whether it could ultimately lead to greater survival rates among women at risk for developing cancer requires understanding how breast density is determined and why it matters.

For a start, breast density is a subjective measurement, said radiologist Jennifer Johnston of the Betty Ford Breast Cancer Center at Lemmen-Holton Hospital in Grand Rapids, Michigan. A given sample is classified as falling within one of four quartiles: mostly fatty, scattered, heterogeneously dense, or extremely dense.

Fatty breast tissue presents fairly clearly in a mammogram; denser breasts will be less sensitive to the same study because the tissue can obscure small masses that occur with more frequency. Physicians call this “the masking effect,” Johnston said.

But even excluding the masking effect, women with dense breasts have a slightly increased baseline risk for developing breast cancer.

“If you look at studies that compare average-density patients to those in the scattered or heterogeneously dense range, about 10 percent is fatty, 40 percent is scattered, 40 percent is heterogenous, 10 percent is extremely dense,” she said. “So women with dense breasts would fall in those two upper categories, and that’s about 50 percent.”

Within that subset of dense-breasted women are those who have additionally increased risks of developing breast cancers from genetic mutations, a personal history of breast cancer, or a significant family history of the same; i.e., a first-degree relative with a history of pre-menopausal breast cancer, Johnston said.

Lori Fontaine, vice president of clinical affairs for medical device manufacturer Hologic, describes the significance of breast density as a unique marker in that it “simultaneously influences both a woman’s risk for breast cancer while also impacting the efficacy of the screening test itself.”

“Breast density is somewhat determined by genetics, but can also change in a woman across her life, depending on factors like her age, and even if she is taking certain medications,” Fontaine said. “Every woman’s profile is unique, but in general, it’s important for women to know what their breast density is because women with very dense breasts are four to five times more likely to develop breast cancer than women with the least dense breasts.”

“It’s our hope and belief that when women know about their breast density and how it relates to their risk for developing breast cancer, they will be more inclined to stay on top of their breast screening, which is crucial for detecting cancer early on,” she said. “It can also help a physician determine what screening modality is best to use for each individual patient.”

Jean K. Warner, director of the Tyanna O’Brien Center for Women’s Imaging at Mercy in Baltimore, said she helps patients model the entirety of their breast cancer risk through a holistic series of assessments that determines whether a patient is at high, normal or average risk for breast cancer.

The high-risk protocol involves annual mammography with supplemental screening modalities; Warner believes in breast MRI as the most sensitive imaging tool for finding breast cancers. Women who are at average risk of breast cancer based on their initial mammograms are trickier to sort out, she said. For average-risk patients with dense breast tissue, breast tomosynthesis or supplemental ultrasound can detect additional cancers that might be masked by a mammogram.

“If you take 1,000 women who are having a screening mammogram, we’re typically going to find between two and seven cancers,” Warner said; “in our practice, it’s around five or six cancers.”

“If you take 1,000 women with dense tissue who’ve already had a normal mammogram, and we do ultrasound, we’re going to find three additional cancers in that group,” she said.

The downside of ultrasound is that it can lead to false positives, which Warner said can drive additional follow-ups and biopsies that ultimately may or may not be necessary.

“Most patients are amenable to doing that additional screening,” she said. “There are other patients for whom doing all that makes them so worried and anxious that they would rather not. If they’re motivated to do that, we’re happy to work with them through the process.”

The innate value of the supplemental modalities is built around taking a 3D model of the breast (a three-dimensional organ) versus the 2D study that mammography offers. Johnston points out that some patients have issues with their insurance companies “giving some grief over having those [supplemental] studies performed ubiquitously,” which can lead to at-risk patients declining to proceed with a study that might be beneficial for their health. Some companies will authorize annual studies; some will only authorize semi-annual studies, and others will deny coverage for them outright, she said.

“There’s no uniformity, and that’s really unfortunate, because it really reduces the need for patients having to come back,” Johnston said.

On the other hand, secondary screening can often uncover imaging artifacts that aren’t necessarily malignant. The increased sensitivity of an ultrasound or digital tomography study can be useful for patients with dense breasts, but it may also increase the risk of false positives, which is why Johnston won’t recommend its general use in patients who aren’t at an increased risk for developing breast cancer.

“In daily practice, it’s helpful to have,” she said. “In the long run, is it making that much of an impact? I don’t know if I can say that. I like to think of the breast as Pandora’s box. You’re going to find something, you don’t know what it is, and it’s going to result in unnecessary biopsies and benign results.”

Having said that, Johnston also points out that “very few patients are disappointed with a benign result on their biopsy,” and that the “false positive biopsy phenomenon” can be a fear tactic that keeps people from receiving necessary screenings.

“You don’t hear that type of thing from any other cancer other than breast cancer,” she said. “If you have an index of suspicion that something could be a breast cancer, I want to know. We don’t have the tools currently to be able to determine which breast cancers are going to become aggressive and result in a patient’s death, and which are not. Until we do have those tools, I don’t think we can be cavalier in dealing with them. Screening is very important, but over-screening can be detrimental.”

For radiologists like Johnston, density inform laws are useful to alerting patients that they might need additional follow-up, but without context, they fear there’s a risk that the message might not be communicated clearly. If the law requires providers to have conversations about the density of their breasts, Johnston worries that providers aren’t clear on where to next take the conversation.

“The difficult thing is that, as the radiologist, you are not in direct communication with your patient,” she said. “You’re in communication with the primary providers who are in the front line dealing with patients and getting them recommendations for their screenings.

“By the time patients see me, their head is filled with whatever their [doctors’] recommendations are,” Johnston said.

“They’re confused about how old they should start, how frequently they should be coming, if they should be doing any supplemental screening on top of mammography,” she said. “I would hope we can come to some kind of consensus nationally as a cohort of physicians to inform our patients so that more of them have appropriate care.”

Johnston would like the information that patients receive about the density of their breast tissue to be contextualized with whatever implications it carries for their personal risk factors, and whether supplemental screening methods would be beneficial for them. In order to drive those details home, Johnston argued for greater collaboration between the different specialists involved in a patient’s care, from gynecologists to primary care providers to radiologists, “so we can have a cohesive narrative to give to patients.”

To Warner, the change of having a federal law versus state-by-state laws is a positive development for patients, but she also noted that the work will have to be done by providers to educate patients about the significance of the notification and its implications for their future treatment.

“I think there will be issues about the whole process, but it’s really going to be an educational tool,” Warner said. “I’m a huge advocate for risk assessment, and we would love to see more of that in other practices.”

Warner said she’d like to see advancement of other complementary risk assessment tools for women’s health, including genetic counseling, which can provide valuable insight into risk factors for women who are younger than the typical screening age for a mammogram.

“We think there are a lot of women with genetic abnormalities, and they don’t know it,” Warner said. “It’s a big-time failure of medicine to have women out there whose family history indicates that they should get genetic testing, and they’re not getting it. It’s a whole part of education that needs to happen.”

Warner is also an advocate for breast MRI, which she described as the most sensitive imaging modality for breast cancer screening. Breast MRI can detect three times as many cancers as can mammography alone, but because it’s more expensive and technologically complex to administer, it’s not a common enough option.

“We think that finding another way of imaging the breast to more accurately image cancers earlier would prevent more,” Warner said.

Warner would like to have dedicated breast MR machines and dedicated breast ultrasound units in her practice, and said she’s following along with research that’s underway on how to perform breast MRI without requiring a contrast agent.

“I think that some of us had hoped that tomosynthesis would be the panacea, but it’s not, for dense breasts especially,” Warner said. “But there’s so many things that women need to understand about breast density and breast health.”

Johnston also cautioned that the media attention around breast imaging contributes to work that must be done by practitioners to keep the public focus on the most salient points of the issues.

“You have the same screening issues, the same bad outcomes, the same false positives, and even higher risks in other cancer screening modalities, but they don’t quite get the same media attention that breast imaging does,” she said. “I am thankful for that in that it makes people aware that [screening is] something they need to have done, but at the same time, it can get in the way of doing what’s best for my patients.”

Dr. Constance Chen, board-certified plastic surgeon and clinical assistant professor of plastic surgery at Weill Cornell Medical College said that some women with dense breast tissue may opt for prophylactic mastectomies so as to obviate the risk of breast cancer altogether. Such patients usually opt for the procedure “when they have either a family history, or a genetic mutation, or they’re tired of dealing with endless biopsies,” Chen said.

“When you have a patient who has dense breasts, and they’re undergoing surveillance every three or six months, and it’s difficult to read, and they’re undergoing biopsy after biopsy, it’s death by 1,000 cuts, and they just want to move on,” she said. “A lot of patients who’ve seen their family members die, they discover they have a genetic mutation, they get a mastectomy, and they feel they’ve been given a lifeboat.”

Chen’s solution is a microsurgical reconstruction of the breast. Using fat and skin grafts from other parts of the patient’s body to recreate her breasts with her own tissue, she’s able to restore sensation by reconnecting the nerves and the blood vessels. If the patient’s mastectomies are nipple-sparing, Chen said that often no one would be able to tell the surgeries were ever done.

“When you use someone’s own tissue, it’s really hard to tell that they’ve had mastectomies,” she said. “You don’t have breast tissue, so it’s almost impossible to have breast cancer when you’ve had a mastectomy.”

Although access to screening can always be an issue for reasons of cost, availability of technology or insurance coverage, Chen said she believes “any number of insurance companies will approve prophylactic mastectomies for people just because they have dense breasts and they’re harder to read.”

“Access is always an issue, and again, it’s the emphasis on trying to keep costs low that makes access worse,” she said. “The dollars are shrinking. I think people should get the best mammogram they can every year.”

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