Changes in breast density over time may be linked to breast cancer risk, study finds

CNN
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Breast density is known to decrease naturally as a woman ages, and now a study suggests that the longer it takes for breast density to decrease, the more likely a woman is to develop breast cancer.

Researchers have long known that women with dense breasts have a higher risk of breast cancer. But according to the study, published last week in the journal JAMA Oncologythe rate of change in breast density over time also appears to be associated with the risk of cancer diagnosis in that breast.

“We know that invasive breast cancer is rarely diagnosed in both breasts simultaneously, so it is not surprising that we observed a much slower decline in the breast that eventually developed breast cancer compared to the natural decline in density with age,” Shu Jiang said. , associate professor of surgery at Washington University School of Medicine in St. Louis and first author of the new study, wrote in an email.

Breast density refers to the amount of fibrous and glandular tissue in a person’s breasts compared to the amount of fatty tissue in the breasts – and breast density can be seen on a mammogram.

“Because women have their mammograms annually or every two years, the change in breast density over time is naturally available,” Jiang said in the email. “We should take full advantage of this dynamic information to better inform risk stratification and guide more individualized screening and prevention approaches.”

The researchers, from Washington University School of Medicine in St. Louis and Brigham and Women’s Hospital in Boston, analyzed 10-year health data among 947 St. Louis-area women who had routine mammograms. A mammography is an x-ray image test that doctors use to look for early signs of breast cancer.

The women in the study were recruited from November 2008 to April 2012 and had mammograms through October 2020. The average age of the participants was approximately 57 years old.

Among the women, 289 cases of breast cancer were diagnosed and researchers found that breast density was higher at the start of the study for women who later developed breast cancer compared to those who stayed. cancer-free.

The researchers also found that there was a significant decrease in breast density in all women over the course of 10 years, whether or not they developed breast cancer later, but the rate of decrease in density over time course was significantly slower among breasts in which cancer was diagnosed later.

“This study found that assessing longitudinal changes in breast density from digital mammograms may offer an additional tool for assessing breast cancer risk and subsequent risk reduction strategies,” the researchers wrote. .

Not only is breast density a known risk factor for breast cancer, but dense breast tissue can make mammograms harder to read.

“There are two issues here. First, breast density can make it harder to completely “see through” the breast on a mammogram, like looking through ground glass. So it can be more difficult to detect breast cancer,” said Dr. Hal Burstein, clinical researcher at the Breast Oncology Center of Dana-Farber Cancer Institute, who was not involved in the new study, said in an email. “Second, breast density is often thought to reflect estrogen exposure or estrogen levels in women, and the higher the estrogen exposure, the higher the risk of developing breast cancer.”

In March, the United States Food and Drug Administration released updates to its mammography regulationrequiring mammography establishments to inform patients of the density of their breasts.

“Breast density can have a masking effect on mammography, where it can be more difficult to find breast cancer in an area of ​​dense breast tissue,” Jiang wrote in her email.

“Even when you rule out finding it, breast density is an independent risk factor for developing breast cancer. reason is unclear,” she said. “It may be that the development of dense tissue and cancer are related to the same biological processes or hormonal influences.”

The results of the new study demonstrate that breast density is a risk factor for breast cancer – but women should also be aware of their other risk factors, said Dr Maxine Jochelson, head of breast imaging at Memorial Sloan Kettering Cancer Center in New York, who did not participate in the study.

“It makes sense to some degree that the longer your breast stays dense, theoretically, the more likely it is to develop cancer. And so basically that expands on the data that dense breasts are at risk,” Jochelson said, adding that women with dense breasts should request additional imaging when having mammograms.

But other factors that can increase the risk of breast cancer include a family history of cancer, excessive alcohol consumption, a biopsy of a high-risk lesion in the breast, or a certain genetic mutation.

For example, women should be aware that “density may not affect their risk as much if they have the breast cancer BRCA 1 or 2 mutation, because their risk is so high that it may not make it much higher. high,” Jochelson said.

A few ways to reduce the risk of breast cancer include maintaining a healthy weight, being active, drinking alcohol in moderation or not at all, and for some people taking medications like tamoxifen and breastfeeding your children if possible.

“Breast density is a modest risk factor. The “average” woman in the United States has a 1 in 8 chance for life of developing breast cancer. Women with dense breasts have a slightly higher risk, about 1 in 6 or 1 in 7. Thus, the lifetime risk increases from 12% to 15%. This still means that most women with dense breasts will not develop breast cancer,” Burstein said in her email.

“Sometimes radiologists recommend additional breast imaging for women with dense breast tissue during mammograms,” he added.

THE US Task Force on Preventive Services – a panel of independent medical experts whose recommendations help guide doctors’ decisions – recommends biannual screening for women over 50. The task force says the decision to start screening earlier “should be individual.” Many medical groups, including the American Cancer Society And Mayo Clinicpoint out that women have the option of starting screening with a mammogram every year from the age of 40.

“It is also very clear that breast density tends to be higher in younger women, pre-menopausal women, and for almost all women it tends to decrease with age. However, breast cancer risk breast increases with age. So those two things are a bit at odds with each other,” said Dr Freya Schnabel, director of breast surgery at Perlmutter Cancer Center at NYU Langone and professor of surgery at NYU Grossman School of Medicine in New York, who was not involved in the new study.

“So if you’re a 40-year-old woman and your breasts are dense, you might think that’s really age-appropriate,” she said. “The take home message that’s very, very practical and pragmatic right now is that if you have dense breasts, whatever your age, even if you’re postmenopausal – maybe even specifically, if you’re postmenopausal – and that your breasts don’t become less dense than the average woman, that’s really a reason to seek out additional imaging in addition to mammography, to use additional diagnostic tools, like ultrasound or maybe even the MRI, if there are other risk factors.