What are dense breasts and why should you know?

After your mammogram, you will receive an email that begins: “Your mammogram indicates that you have dense breasts.” When I received this letter, I did not quite know what it meant or what, if anything, I should do. Off the mail to a pile of other “non-urgent” mail to think about later.

Later on now. This is because the US Food and Drug Administration has released a new rule on breast density notifications, as part of an update to mammography guidelines. Published on March 10, the rule mandates these letters to make demands on the nation and the information they contain. Previously, 38 states notified people with dense breasts or information about breast density after a mammogram. The new rule, which goes into effect on September 10, 2024, means that everyone who has had a mammogram will be informed whether their breasts are dense or not.

Why do people need to know this? If you want to take the message home, here it is: Dense breasts modestly increase the risk of being diagnosed with breast cancer. But breast density is one factor to be considered among others, remaining with a person’s overall risk. Dense breasts do not mean you will have breast cancer, and dense breasts do not mean you are clear.

Ideally, receiving a notification about breast density will suggest a more detailed discussion about your breast cancer risk with your doctor. This column cannot replace that. But read on if you’d like to learn more about dense breasts and why the focus on them is somewhat of a blunt instrument.

What thick breasts?

Breasts are made up of different types of tissue: glandular, which produces milk and directs it to the nipple, plus tissue (fibrous) and fatty tissue. Dense breasts have more glandular and connective tissue than fatty tissue.

Dense breasts are “not abnormal,” says internist and epidemiologist Joann Elmore at UCLA. Thick breasts are common too: About 46 percent of women ages 40 to 79 in the United States have them, researchers reported in Journal of the National Cancer Society in 2019

A radiologist visually assesses the density of breast tissue from a mammogram. The two non-dense classifications are “almost completely fatty” and “scattered areas of fibroglandular density,” that is, mostly fatty tissue with some areas of dense tissue. About 8 and 46 percent of the United States ages 40 to 79 have those two classes, respectively.

The two dense categories are “very dense” and “very dense” with an estimated 40 percent and 6 percent of US women 40 to 79 in these categories, respectively. The two types of dense are usually joined together and are called dense breasts. Under the new FDA rule, the notification letter will be written in this way: a person’s breast is “dense” or “not dense.”

One thing: Breast density can change. For example, older women tend to have less dense breasts than younger women. Sometimes, however, it will change from “dense” to “non-dense” or vice versa, depending on the radiologist reading the mammogram and deciding between the “dense asps” and “heterogeneous dense” types.

OK, so what do I need to know if I have dense breasts?

Thick breasts two doubts. First, on a mammogram, the glandular and connective tissues show up as white – which is how tumors or other abnormal breast tissue look too. The radiologist was looking for such a dense tissue that it could hide itself.

One measure of how well a mammogram works is sensitivity, the ratio of tumors detected by a mammogram out of all tumors detected (whether found by a mammogram or not). An analysis of mammograms from a Dutch screening program found that for those with almost all fatty tissue, the sensitivity was 86 percent, and for areas of sparse density it was 78 percent. The sensitivity continued to drop in the denser: 70 percent for the densest heterogeneous breasts and 61 percent for the densest breasts, the researchers reported in Breast Cancer Research and Treatment in 2017

Second, the dense body itself contributes to the risk of cancer. This may be related to the greater amount of dense glandular tissue in the breasts. “Breast cancers almost always grow in glandular tissue,” says Priscilla Slanetz, a breast radiologist at Boston Medical Center.

How much do dense breasts increase the risk of a breast cancer diagnosis?

shame Thick breasts “raise you above the average person a little,” says Slanetz. The average person is anyone with no known risk factors for developing breast cancer.

The researchers compared the risk of developing breast cancer in those with dense breasts with the most dense non-dense categories, in areas of dispersed density. Premenopausal women with heterogeneously dense breasts are at 1.5 to 1.8 times greater risk of developing breast cancer, depending on race and ethnicity. Those with denser breasts have a 1.8 to 2.4 times greater risk. For postmenopausal women, the risk was 1.3 to 1.6 times higher for heterogeneously dense breasts and 1.5 to 2 times higher for very dense breasts, the researchers reported in Cancer Epidemiology, Biomarkers & Prevention in 2020

Here’s another way to try to explain the risk, based on a hypothetical case study of a 47-year-old woman with heterogeneously dense breasts and no family history of cancer. Among 1,000 women like those in the study of heterogeneously dense breasts, an estimated 20 will develop breast cancer in the next 10 years. This compares with 13 1,000, as the case studies of women, but with the most common non-dense categories.

It is also important to know that breast density is not associated with a higher risk of dying from breast cancer, the researchers reported Journal of the National Cancer Society in 2012 An analysis of more than 9,000 women with breast cancer suggests that what contributes to the development of cancer differs from what affects the risk of dying from breast cancer. Another group of researchers also reported in 2018 that there was no association between breast density and cancer-like death.

What other factors should I consider the risk of breast cancer?

Thick breasts are one part of the risk picture. The two biggest risk factors for developing breast cancer are women and getting older, Slanetz says.

About 1 in 8, or 13 percent, of cisgender women in the United States will be diagnosed with cancer in their lifetime. An estimated 297,790 new cases of breast cancer are expected in women in 2023. Males account for less than 1 in 100 cases (SN: 10/3/19). And the risk rises as birthdays do: On average, while 1 in 65 women starting at age 40 will develop breast cancer in the next 10 years, 1 in 24 women starting at age 70 will, according to the National Cancer Institute.

There are also racial differences in breast cancer risk. Despite a slightly lower incidence of breast cancer than white women, black women have a 40 percent higher risk of death: 28 per 100,000 black women die of breast cancer in the United States compared with 20 per 100,000 white women. Black women are diagnosed with breast cancer at a younger age, have more aggressive disease and are diagnosed with cancer later, all of which contribute to a worse prognosis. Inequalities in access to cancer therapy and surgical treatment contribute to the disparity.

Fewer cancers have been reported for transgender men and women. Researchers have found that transgender men have lower cancer rates than cisgender women, which appears to be related to the surgical removal of the breasts and the use of testosterone. Transgender women have a reduced risk of breast cancer compared to cisgender women due to less exposure to the hormone estrogen throughout their lives, although estrogen therapy may increase the risk.

Among the factors that increase the risk of developing breast cancer are: BRCA1 and BRCA2 genetic changes. About 7 in 10 carriers of one of the mutations will have breast cancer by the age of 80. Women who have received chest radiation to the chest, as well as children, are also at high risk. These two groups have specific recommendations for breast cancer screening.

Online breast cancer risk calculators can help doctors estimate a person’s risk. With these additional risk factors, people are considered high risk if they have a 20 percent or greater chance of developing breast cancer in their lifetime. The American College of Radiology recommends mammograms starting at age 30 for high-risk patients, supplemented by breast magnetic resonance imaging. The ACR also recommends that black women be evaluated for breast cancer risk no later than age 30.

People with dense breasts — like those outside, and anyone who is at moderate or slightly above average risk — should still get screening mammograms, doctors say. Medical associations vary in screening recommendations about what age to start and whether to get mammograms annually or every other year.

What should I do if I have thick breasts?

There are no specific recommendations for dense breasts to guide men or their doctors. People need information about their breast density, says Ilana Richman, a general internist at Yale School of Medicine. “But the open question is what to do with that information,” he said, because of the lack of regulations.

Some notification states have suggested that people with dense breasts may benefit from supplemental screening with other imaging technology, such as MRI or ultrasound. With the new FDA rule, the notifications say that in some dense tissue, in addition to other imaging tests to find cancer. But density alone is not enough to bump someone into the highest risk category and require additional screening, says Karla Kerlikowske, a primary care physician and clinical epidemiologist at the University of California, San Francisco. “There are a lot of people who have dense breasts who are at low risk of breast cancer,” he said.

Ideally, the notification of a dense breast would lead to a discussion with the doctor about the different risks of cancer, to understand a person’s overall risk. However, there is a limited period of primary visitation in the United States. “We don’t have a system that allows enough time for that nuanced discussion,” says Christina Chapman, a radiation oncologist and equity researcher at Baylor College of Medicine in Houston.

Plus, the conversation should be done with people who also don’t have dense breasts, who may still be at high risk. “The focus on chest density distracts in some ways from the idea that risk is multidimensional,” says Richman.

Many women who develop breast cancer have no apparent risk factors, Planetz says, which is why screening mammograms are so important. “We screen” [everyone] because it must.”