What It Means To Have 'Dense Breasts' — And Why It Matters

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Not only is it harder to detect cancer in denser breasts, they’re also linked to an increased risk of developing cancer in the first place. (Bob Stone/Corbis)

The statistics are frightening: Women have a one in eight chance of developing breast cancer. And over 200,000 new cases of breast cancer are expected to be diagnosed each year in women in the U.S., largely thanks to screening programs that use mammography to find cancer as early as possible. But while breast cancer screening can help save lives, it’s not as straightforward a process as many women believe.

“The whole breast cancer screening controversy has become more and more of an issue over the past several years,” says Eric Winer, MD, the director of breast oncology at the Susan F. Smith Center for Women’s Cancers at Dana-Farber Cancer Institute, and a spokesman for the American Association for Cancer Research. “It’s far less clear than it once was exactly what a woman, particularly a younger woman, should do in terms of breast cancer screening.”

One of the biggest issues with current screening protocols is that the younger a woman is, the harder it is to tell if she has cancer because her breasts are denser. Breast density is an important factor in mammography — so much so, in fact, that some states like Connecticut actually require radiologists to inform a woman if she has dense breasts. But what exactly does that mean?

Breast density refers to the ratio of fatty tissue, which appears black on a mammogram, to various kinds of fibrous tissue, which appears white. The first trouble with having denser breasts is that cancers appear white, too.

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(Susan G. Komen)

“When you have dense breasts, what you see is all white, and that’s why we cannot see the tumors very well,” explains Edith Perez, MD, deputy director at large for the Mayo Clinic Cancer Center and the Serene M. and Frances C. Durling professor at the Mayo Clinic College of Medicine.

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Breast density changes for all women with age. “The older a woman gets, the less dense the breasts tend to be.” Perez tells Yahoo Health. In fact, this is why doctors don’t start screening for cancer until women are 40. “In younger women, the breast density is such that we cannot see tumors when they are present.”

Denser breasts not only make it harder to detect cancers, they are also linked to an increased risk of developing cancer in the first place. Instead of the “one in eight”, says Perez, “it may be one in seven-and-a-half — it’s a slightly increased risk as compared to the general population, but it’s clearly there.”

“Biologically, we think that breast density is tied to estrogen, so the higher estrogen levels you have, the more density you may have,” says Anees Chagpar, MD, associate professor of surgery at Yale School of Medicine and the director of the breast center at Smilow Cancer Hospital at Yale-New Haven. Estrogen levels are higher in younger women, hence why younger women have denser breasts, but they’re also linked to increased cancer risk. But breast density is not as clear-cut in terms of its risk as other factors. “It’s hard to specify an exact risk that density conveys because there’s varying degrees of density,” Chagpar says to Yahoo Health. “From a radiographic standpoint, they’ll talk about heterogeneously dense or extremely dense, and each of these carries a different risk.”

So how can you tell what your risk is? Unfortunately, you can’t know if you have dense breasts on your own, explain the doctors. The perkier and firmer your breasts feel, the more dense they may be, but there are ligaments and other tissues that cause hardness or lumps that are unrelated to the amount of fibrous tissue. Larger breasts may be less dense because they are fattier, but there isn’t a strong connection, nor are there strong connections to ethnicities. Since breast density is really a radiographic diagnosis, a mammogram is necessary to be sure.

Even if you think you have dense breasts or have been told you have them, though, there’s no reason to panic. “The last thing that we want is for women to think that increased breast density is some new disease,” says Winer. “It’s nothing that people should be particularly alarmed about.” And if you do have dense breasts, you’re certainly not alone — half of women under 50 have dense breasts, while around a third of women over 50 do.

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Furthermore, a study just came out that suggests there’s hope. As Jean Weigert, MD, lead author of the study and director of breast imaging for the Hospital of Central Connecticut explains, using additional screening technologies like ultrasound can help improve detection of cancers in women with dense breast tissue.

Weigert, with the help of a medical student from the University of Connecticut, received data from 12 clinical sites around the state. That amounted to more than 90,000 mammograms and about 10,000 bilateral breast ultrasounds in the first year, from which the team found 3.2 breast cancers per thousand that mammograms missed.

The downside was that increased ultrasound use also led to increased false positives — breasts that were biopsied even though they didn’t have cancer. “But that being said, we found cancers that wouldn’t have been found, and the only risk factor in most of these women was that they have dense breasts,” says Weigert.

The study continued for four years, and each year, the number of false positives went down while the study continued to find around the same number of previously missed cancers — around three per thousand screens. “There was a learning curve,” explains Weigert. “Every time there is a new technology, it takes time before you utilize it properly.”

While ultrasound technology is far from new, it has only been applied to the search for breast cancer in the past few years. And it’s not the only tool in doctors’ belts when it comes to finding cancer in dense breasts: Molecular imaging, 3D mammography, and even blood tests are on the horizon and may be even better than ultrasounds at detecting cancers.

While the study’s results are promising, not all are convinced. “I don’t think most people believe that we should be doing ultrasounds routinely in all women who have dense breasts,” says Winer. He does, however, note that women with dense breasts who have other risk factors should talk to their doctors about further screening options. Perez says that “the field has moved beyond ultrasound,” and thinks that newer methods will be the go-to for additional screening in the future.

But Weigert notes that such technologies are expensive and not readily available in most states. Her hospital in Connecticut, for example, doesn’t have a 3D mammography machine. “Ultrasound is readily available.” And while she is hopeful that newer technologies will eventually replace ultrasounds for additional detection, “that’s a when. It’s not a now.” 

The crux of the problem, though, says Weigert, is that health insurance doesn’t currently cover additional screening in many states. While mammography is covered under Obamacare, ultrasounds and other advanced screening technologies are instead coded as diagnostic tests, which have to be paid for separately. She hopes that legislation can ensure that advanced screens are re-coded as the screening technologies they are to ensure that all women can afford them.

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