Good News for Women With Dense Breasts: No Higher Risk of Breast Cancer Death

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Women with dense breasts are considered at a higher risk of developing breast cancer, in part because their tumors can be harder to spot on a mammogram. But a recent and reassuring study finds that despite their slightly increased risk, these women are no more likely to die of breast cancer than those whose breasts have more fat tissue.

So, even if the women’s tumors are caught later, they don’t appear to be any more aggressive or any harder to treat than other women’s tumors, the study found. The study did note a higher risk of death in some women, however: those with less dense breasts who were also obese or had very large tumors. Why that’s so isn’t clear; further study is needed.

“It shows we have a lot to learn about dense breast tissue and its implications for screening, diagnosis and treatment,” Barbara Monsees, chairwoman of the American College of Radiology’s breast imaging commission, told USA Today, commentingthat the study results were a bit surprising. Monsees wasn’t involved in the study.

(MORE: Study: For Some Women in their 40s, Routine Mammograms May Be Worth the Risks)

Whether a woman is classified as having dense breasts is a judgment call that can vary from doctor to doctor and from one year to the next, the AP reported:

Radiologists divide density levels into four categories. According to the American College of Radiology, about 10 percent of women have almost completely fatty breasts. Another 10 percent have extremely dense breasts, the level that [study co-author Dr. Karla] Kerlikowske said is linked to a higher risk of developing cancer. The rest are in between, with about 40 percent having scattered areas of density and 40 percent having fairly widespread density, categories especially difficult to classify.

Spotting cancer on a mammogram can be tough because while fat tissue shows up dark on the scan, both dense tissue and tumors appear white.

In the new study, published in the Journal of the National Cancer Institute, researchers looked at 9,232 women diagnosed with invasive breast cancer between 1996 and 2005 and followed them for an average of about 6.5 years. The researchers assessed each woman’s breast density from her mammogram and rated it on a scale of 1 to 4; women receiving a score of 1 had low-density breasts, while those getting a 4 had very high-density breasts. The vast majority of women — about 84% — fell into categories 2 or 3, the fuzzier middle of the spectrum.

By the end of the follow-up period, about 1,800 women had died, 889 from breast cancer and 810 from other causes. The researchers found that women with high-density breast tissue did not have an increased risk of death from breast cancer compared with women with lower breast density.

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The study’s findings add to the discussion over the necessity of telling women that they have dense breasts and then recommending that they get additional screening, such as ultrasound or MRI, which can sometimes detect tumors that mammograms miss. In a statement, the authors said:

State legislatures have passed and continue to pass laws requiring radiologists to notify women that they have dense breast tissue. Some of these laws actually mention that women might want to participate in MRI and/or ultrasound screening because they have dense breasts. However, it is unknown if such screening can actually benefit them in terms of saving lives.

Indeed, there’s no data to suggest that these extra expensive tests save lives. What’s more, they tend to lead to more false alarms, causing women unneeded stress and unnecessary treatments. Meanwhile, four states — Connecticut, Texas, Virginia and New York — have passed laws requiring health-care providers to inform women if their mammograms show they have dense breasts.

And while that information can be potentially useful, it’s still not clear exactly how. Breast density must be considered along with a woman’s other cancer risk factors, like family history, for example, as well as her age. Breast density tends to decrease naturally as women get older, so it’s possible that a 60-year-old with dense breasts might be at greater risk than a younger woman with the same density.

As Dr. Otis Brawley of the American Cancer Society, pointed out to the AP: “We’re making policy in a gray area where the experts and doctors don’t know what it means.”

MORE: Higher Risk for Women With False-Positive Mammogram Results