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How Much Does Dense Breast Tissue Increase Cancer Risk

Study Suggests Dense Breast Tissue Isnt Always A High Cancer Risk

Does Dense Breast Tissue Raise Cancer Risk? Dr. Neil B. Friedman, Mercy Medical Center Baltimore
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By Denise Grady

  • May 18, 2015

A new study offers help to patients and doctors who are trying to deal with mammogram results that many women consider troubling and confusing: the finding of dense breast tissue.

Not only is breast density linked to an increased risk of cancer, it also makes cancer harder to detect because dense tissue can hide tumors from X-rays. But the new research indicates that not all women with dense breasts are at very high risk.

Patient advocates urge women with dense breasts to ask doctors about extra tests like ultrasound or an M.R.I. to check for tumors that mammography might have missed. Studies have found that those exams can improve detection of tumors over mammography alone in dense breasts.

Pressed by advocacy groups, 22 states have passed laws requiring that breast density be reported to mammography patients, and similar federal legislation has been introduced in the House and the Senate.

The new study, published on Monday in Annals of Internal Medicine, suggests that only about half of women with dense tissue are at such a high risk that they need extra tests. Instead of looking at density alone, women and their doctors should also consider other risk factors when making decisions about additional screening, the researchers concluded.

We hope this work can help women be better informed regarding whether or not supplemental screening, such as with ultrasound or with M.R.I., should be considered, she said.

Will My Health Insurance Cover It

Nationwide recommendations do not advise women with dense breasts to have more frequent screenings. However, some states require that insurance cover more frequent breast cancer screenings for those with higher breast density.

Women with dense breasts should talk to their doctor about other cancer risk factors and protective measures and work together to make a screening plan, Mandal says.

Essential information will be included in the mammogram report that goes to your doctor and the patient letter you receive giving you the results of your mammogram. This is mandated by state and federal laws.

Breast Density And Mammograms

Dense breasts can’t be felt through a clinical breast exam, so the only way to find out whether you have dense breasts and thus an increased cancer risk is by getting a mammogram.

But it’s important to note that dense breasts can make it more difficult for radiologists to read a mammogram since dense fibroglandular tissue shows as white on mammograms, similar to how tumors appear. This can “hide” tumors and make it more difficult to read a mammogram of a dense breast. Still, the increased cancer risk is separate from the ability to read a mammogram, says Mandal.

Scientists are currently studying whether other breast-imaging options can provide a better picture of dense breasts. There are multiple studies demonstrating that both breast ultrasound and breast MRI can significantly increase the detection of breast cancer in women with dense breast tissues.

Anyone with dense breasts who is concerned about cancer detection should talk to their doctor about the following screening options, Mandal says. Mammography should always be included in addition to other options, however, none of the additional modalities have demonstrated a decrease in breast cancer mortality.

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Characteristics Of Dense Breasts

Breasts are composed of fibrous, glandular, and fatty tissue. A woman’s breasts are considered dense if they have less fat and more glandular and fibrous tissue than average.

There are four categories used to describe breast density:

  • Breasts that are the least dense have almost all fatty tissue
  • Breasts that have scattered areas of fibroglandular density
  • Breasts with heterogeneous density
  • Breasts that have almost all glandular and fibrous tissue with little to no fatty tissue.
  • Dense breasts are more common among women who are young and postmenopausal women who take hormone therapy for symptoms of menopause.

    Breast Cancer Risk Factors You Cannot Change

    Dense Breasts

    A risk factor is anything that increases your chances of getting a disease, such as breast cancer. But having a risk factor, or even many, does not mean that you are sure to get the disease.

    Some risk factors for breast cancer are things you cannot change, such as getting older or inheriting certain gene changes. These make your risk of breast cancer higher.

    For information on other known and possible breast cancer risk factors, see:

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    Differences Between The Various Hormone Replacement Therapy Regimens

    As noted , most observational studies that were able to provide results on both sequential and continuous-combined regimens found that the BC risk was greater with the latter, particularly when HRT use was longterm . A comparison of the findings obtained in the different countries is rendered difficult because the estrogens employed also vary. Nevertheless, risk differences between sequential and continuous-combined regimens seemed more marked and consistent in studies conducted in Northern European countries than in those conducted in the US . This might partly be due to the fact that in the US, particularly in some states , the sequential regimen could have been privileged in women thought to be, and actually being, at high BC risk, because of widely advertised data suggesting a protective effect of the sequential regimen . More importantly, in Northern Europe the daily dose of 19-Nortestosterone-derived progestins was the same in both continuous-combined and sequential regimens, so that the monthly cumulative dose in the former was twice that of the latter, while in the US the daily MPA dose in combined regimen was much lower than that given in sequential regimen , so that cumulative dose did not differ greatly between them.

    What Affects Breast Density

    High breast density is common. In the U.S., 40-50 percent of women ages 40-74 have dense breasts .

    Breast density varies greatly by age and weight. Dense breasts are more common in both young women and thin women :

    • About 50-60 percent of women ages 40-44 have dense breasts, compared to 20-30 percent of women ages 70-74.
    • About 50-60 percent of women with a healthy weight have dense breasts, compared to 20-30 percent of obese women.

    Medications that contain hormones can also affect breast density. For example :

    • Women who take menopausal hormone therapy tend to have denser breasts than they would if they didnt take MHT. As women age, their breasts become less dense and more fatty. Taking MHT slows this process. MHT is also called postmenopausal hormone use and hormone replacement therapy .
    • Women who take the drug tamoxifen tend to have lower breast density than they would if they didnt take tamoxifen.

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    Should You Worry About Dense Breast Tissue

    Breasts come in different shapes, sizes and densities.

    In some cases, dense breast tissue can be associated with an increased risk of breast cancer.

    A 2017 U.S. study revealed that four in 10 cases of breast cancer in younger women can be blamed on high breast density. The results show that breast density is a much more important breast cancer risk factor to be aware of than a persons family history. But having dense breasts is not an abnormal condition. In the United States, 43% of women over the age of 40 have dense breast tissue. Its basically a physical attribute of the body and theres little anyone can do to actively change or improve the density of their breast.

    What Are Researchers Hoping To Learn About The Relationship Between Breast Density And Breast Cancer

    Dense breast tissue raises cancer risk

    Some important questions include:

    • Can imaging tests such as 3-D mammography , MRI, and ultrasound help provide a clearer picture of breast density?
    • Are there certain patterns or areas of dense breast tissue that are particularly âriskyâ?
    • Why do some women with dense breasts go on to develop breast cancer, while others do not? Can biomarkers be identified that help predict whether breast cancer will develop in a woman with dense breasts?
    • Are changes in breast density over time associated with changes in breast cancer risk?
    • Can women reduce their breast density, and potentially their breast cancer risk, by taking medicines or by applying topical agents directly to the breast?

    NCI’s Division of Cancer Prevention supports research on cancer screening and risk factors, including breast density, such as this clinical trial for women with dense breasts. NCIâs Division of Cancer Epidemiology and Genetics conducts research on risk factors for cancer, as explained in this article that explores the relationship between mammographic breast density and breast cancer.

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    Potential Supplemental Screening Modalities For Women With Dense Breasts

    Over the last several years, multiple imaging modalities have been proposed as supplemental screening tools for women at increased risk of breast cancer, including women with dense breasts. The potential benefits and harms of different supplemental screening modalities currently available to women with dense breasts are summarized in and described in more detail below.

    How Are Dense Breasts Detected

    When radiologists look at your mammogram, breast tissue will show up as black and white. Glandular and dense connective tissue will show up white on a mammogram because X-rays dont pass through as easily. This is why its called dense tissue.

    X-rays pass through fatty tissue easier, so it shows up black and is considered less dense. You have dense breasts if your mammogram shows more white than black.

    These tests are also used to help doctors diagnose potential breast cancer:

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    In Vitro Data Bearing On The Estrogen Augmented By Progesterone Hypothesis

    In vitro studies have established that estrogens markedly increase the mitotic rate of both normal and malignant breast epithelium cells there is also evidence that estradiol and its metabolites are carcinogenetic to human breast epithelium . Conversely, the picture is more complex for progesterone, which may affect mitotic activity of normal and malignant breast cells by various mechanisms and may have proliferative or antiproliferative effects depending on study parameters .

    Breast Density And Breast Cancer Risk In Postmenopausal Women From Harvard Womens Health Watch

    Dense Breast Tissue Signals Higher Risk For Breast Cancer ...

    Having dense breasts that is, relatively little fat in the breast and more glandular and connective tissue, as seen on a mammogram is one of the strongest known risk factors for breast cancer. A recent study finds that higher breast density also boosts the risk of some aggressive types of breast cancer in postmenopausal women, reports the October 2011 issue of Harvard Womens Health Watch.

    Using data from the Nurses Health Study, Harvard researchers found that the link between breast density and breast cancer was stronger for cancer confined to the ducts and lobules than for invasive cancer. But it was also stronger for certain breast cancers associated with poorer outcomes, including larger tumors, high-grade tumors, and estrogen receptornegative tumors .

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    Breast Density May Be Top Indicator Of Cancer Risk

    Study suggests it outweighs obesity and family history, but oncologists say more research is needed

    HealthDay Reporter

    THURSDAY, Feb. 2, 2017 — Women whose breasts are predominantly made up of more dense, glandular tissue face higher odds for breast cancer, a new study finds.

    The researchers added that, based on their study of 200,000 women, breast density may be the most important gauge of breast cancer risk, eclipsing family history of the disease and other risk factors.

    “The most significant finding in this study is the impact of breast density on development of breast cancer in the population,” said study senior author Dr. Karla Kerlikowske. She is a researcher in the department of epidemiology and biostatistics at the University of California, San Francisco .

    Still, not everyone is convinced that breast tissue density is the preeminent risk factor for breast cancer.

    Dr. Kristin Byrne is chief of breast imaging at Lenox Hill Hospital in New York City. She believes that the numbers in the study attributed to risk based on tissue density seem “incredibly high, especially when other risk factors were not taken into consideration.”

    Byrne said, “Before these patients are placed on drugs such as tamoxifen, which have significant side effects and are intolerable for many people, more studies are necessary.”

    Overall, breast density was the most prevalent risk factor for breast cancer, the UCSF team reported.

    Criticism Of Estrogen Augmented By Progesterone Hypothesis

    According to this hypothesis, the increased risk of BC associated with estrogen is augmented substantially by progesterone . The hypothesis is based on some findings from in vitro studies, on the results of in vivo studies on breast cell proliferation, on interpretations of the epidemiological relationship of BC with premenopausal menstrual irregularities and cycle length and, more recently, on the finding that BC incidence and breast density are increased in women who use estrogen plus progestin HRT . However, all these findings are open to different interpretations.

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    Other Steps You Can Take

    If you have dense breasts, there are other steps you can take to care for your breast health. In addition to working with your doctor to consider supplemental screening, you can:

    • Make sure you have a mammogram every 12 months without delay, and try to go to a center with 3D mammography if possible.
    • Perform breast self-exams so that youre aware of any changes in your breasts, which should be reported to your doctor.
    • Follow all of the lifestyle recommendations for reducing breast cancer risk, such as:
    • never smoking

    Visit the Know Your Risk page on for more information.

    Think Pink, Live Green: A Step-by-Step Guide to Reducing Your Risk of Breast Cancer teaches you the biology of breast development and how modern life affects breast cancer risk. of the booklet to learn 31 risk-reducing steps you can take today.


  • National Cancer Institute. Dense Breasts: Answers to Commonly Asked Questions. Available at:
  • Melnikow J, Fenton JJ, Whitlock EP, et al. Supplemental Screening for Breast Cancer in Women With Dense Breasts: A Systematic Review for the U.S. Preventive Service Task Force . Rockville : Agency for Healthcare Research and Quality 2016 Jan. Available at:
  • This content was developed with contributions from the following experts:

    Reproductive History Estrogen Is The Main Hormone Associated With Breast Cancer Estrogen Affects The Growth Of Breast Cells Experts Believe That It Plays An Important Role In The Growth Of Breast Cancer Cells As Well The Type Of Exposure And How Long Cells Are Exposed To Estrogen Affects The Chances That Breast Cancer Will Develop

    Dense Breasts Increase Breast Cancer Risk – Dr. Neil Friedman – Mercy

    Early menarche

    The start of menstruation is called menarche. Early menarche is when menstruation starts at an early age . Starting your period early means that your cells are exposed to estrogen and other hormones for a greater amount of time. This increases the risk of breast cancer.

    Late menopause

    Menopause occurs as the ovaries stop making hormones and the level of hormones in the body drops. This causes a woman to stop menstruating. If you enter menopause at a later age , it means that your cells are exposed to estrogen and other hormones for a greater amount of time. This increases the risk for breast cancer. Likewise, menopause at a younger age decreases the length of time breast tissue is exposed to estrogen and other hormones. Early menopause is linked with a lower risk of breast cancer.

    Late pregnancy or no pregnancies

    Pregnancy interrupts the exposure of breast cells to circulating estrogen. It also lowers the total number of menstrual cycles a woman has in her lifetime.

    Women who have their first full-term pregnancy after the age of 30 have a slightly higher risk of breast cancer than women who have at least one full-term pregnancy at an earlier age. Becoming pregnant at an early age reduces breast cancer risk.

    The more children a woman has, the greater the protection against breast cancer. Not becoming pregnant at all increases the risk for breast cancer.

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    Dense Breasts And Breast Cancer: What Every Woman Needs To Know

    Two new state laws targeting breast cancer screenings and dense breasts have been passed in Illinois since 2018. Still, many women dont know whether they have dense breasts and how that affects breast cancer screenings despite roughly half of all women having dense breast tissue. We spoke with an oncology radiologist who specializes in breast imaging to explain what dense breast tissue means and why it matters.

    What are dense breasts, and why should women know whether they have them?

    Its a term used to describe breasts that have a higher proportion of glandular tissue to fatty tissue. We get worked up about dense breast tissue for two reasons: having dense breasts inherently increases your risk for breast cancer by two to four times, and the denser your breasts are, the harder it is for radiologists to spot cancer. The denser your breasts are, the whiter they look on imaging cancer also looks white. So white on white makes it hard for me to see through that dense breast tissue to find the cancer.

    Why is having dense breasts such a hot topic?

    Weve always known about dense breast tissue, but we never realized its true implications as a cancer risk factor. Now, federal notification laws are sweeping the nation. In Illinois, not only is it required to inform patients they have dense breasts, but insurance companies are required to cover a supplemental screening exam to help screen for women with dense breast tissue.

    How do dense breasts affect self-exams?


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