All breasts contain ducts and their milk-producing glands, fibrous tissue, and fat.  The glands and fibrous tissue (or “fibroglandular” tissue) are referred to as “dense tissue”. Each woman’s breasts are different from the next and contain a unique mix of fatty and dense tissue. Some women have very little dense tissue compared to fatty, some have a lot, and most are in between.   A woman may be considered to have “dense breasts” based on the amount of dense tissue she has, which is determined by a mammogram  (see FAQ #3 for an explanation of how breast density is categorized from a mammogram).

Dense breasts are normal, and not a diagnosis, illness, or condition. Dense breasts are important for two reasons:

1. Dense tissue can hide cancer on a mammogram.

2. Having dense breasts increases a woman’s risk for breast cancer.

Dense tissue blocks x-rays and therefore shows up light gray or white on a mammogram. Most breast masses (whether due to cancer or not) also block x-rays and appear light gray or white on a mammogram, making them difficult to see in dense tissue, where they occur more often. Fatty tissue allows more x-rays to penetrate and therefore shows up as dark gray or black on a mammogram. Breast masses (whether due to cancer or not) are easier to see in fatty tissue.

Diagrams of the normal breast. Left: The normal breast is composed of milk-producing glands at the ends of ducts that lead to the nipple. Fibrous tissue surrounds the glands. There is layer of fat just beneath the skin. Often a few lymph nodes and the underlying muscle are seen near the underarm (axilla). Right: On a mammogram, fat appears dark gray, glands and fibrous tissue (dense tissue), as well as muscle, and lymph nodes appear light gray or white. Masses due to cancer also appear white.

Dense breasts are normal, and not a diagnosis, illness, or condition. All breasts contain ducts and their milk-producing glands, fibrous tissue, and fat.  The glands and fibrous tissue (or “fibroglandular” tissue) are referred to as “dense tissue”. Each woman’s breasts are different from the next and contain a unique mix of fatty and dense tissue. Some women have very little dense tissue compared to fatty, some have a lot, and most are in between. A woman is considered to have “dense breasts” based on the amount of dense tissue she has, which is determined by a mammogram. It is not clear why some women have dense breasts and other do not.

Dense breasts are not unusual but younger women tend to have dense breasts. By age:

• More than half of women under the age of 50 have dense breasts.
• About 40 percent of women in their 50s have dense breasts.
• About 25 percent of women aged 60 and older have dense breasts.

Your breasts are unique and can change over time. During pregnancy and breastfeeding, the dense tissue grows, and the breasts become denser and often larger. Breast density returns to what it was before the pregnancy about 2-3 months after breast-feeding is finished. With menopause, density tends to decrease, but doesn’t always. It is important for you to know your own breast density and what the limitations of mammography may be for your breast type.

Breast density is determined by the doctor (a radiologist) who examines the mammogram images. The radiologist can also use computer software to measure (quantify) the breast density. Breast density is not determined by how a breast looks or feels. The density is categorized as one of four categories (see below) and is usually in the report sent from the radiologist to the referring doctor.

A woman’s breast tissue is described on mammography as one of four categories:
(A) Fatty; (B) Scattered fibroglandular tissue; (C) Heterogeneously dense; (D) Extremely dense

Breasts which are (C) heterogeneously dense, or (D) extremely dense, are considered “dense breasts.”

A. ALMOST ENTIRELY FATTY – On a mammogram, most of the tissue appears dark gray or black while small amounts of dense (or fibroglandular) tissue display as light gray or white. Such breasts are not considered dense.

About 10% of all women have breasts considered to be “fatty.”

Most states now have laws that require breast density information to be included in the letter you receive with your mammogram results. Even if you do not live in a state with a breast density inform law, you can ask your referring health care provider for this information. Breast density is usually in the mammogram report provided to them. Click HERE to see what the breast density reporting requirement is in your state.

Dense breasts are normal. On average, about 40% of women of mammography age have dense breasts. Density tends to decrease as a woman gets older. More than 50% of women in their 40s have dense breasts, about 40% of women in their 50s, just under 30% of women in their 60s, and 25% of women in their 70s.

Though dense breasts are normal, they do matter when it comes to screening for breast cancer, learn more here.

Cancers can be hidden or “masked” by dense tissue. On a mammogram, cancer is white, but normal dense tissue also appears white. If a cancer develops in an area of normal dense tissue, it can be more difficult or sometimes impossible to see it on the mammogram, like trying to see a snowman in a blizzard. If a cancer (white) develops in an area of fat (black or dark gray), it is usually easier to detect even when it is small. Because dense tissue can hide cancers, the more fatty a breast is, the more effective the mammogram is in showing the cancer. As breast density increases, the ability to see cancer on mammography decreases.

Cancer on a mammogram in a fatty breast vs. a dense breast

Yes. In addition to hiding cancers on a mammogram, denser breast tissue is more likely to develop breast cancer. The denser the breasts are, the higher the risk. Women with the densest breasts have a risk for breast cancer that is 4 times higher than that of women with the least dense (fatty) breasts. The majority of women will fall between these extremes.

Most breast cancer occurs in women with no known risk factors other than being a woman and getting older. There are many risk factors that increase the chance of getting breast cancer. These include breast density, family history of cancer (particularly breast and/or ovarian cancer in your mother or sisters), and prior atypical breast biopsies (where breast cells have begun to change into a pre-cancerous state but are not yet cancerous). It is not fully known how breast density, family history, prior biopsy results, and other factors interact to affect breast cancer risk.

Print and discuss the Risk Checklist with your health care provider.

No. Dense breasts are normal and are not unusual. By age:

• More than half of women under the age of 50 have dense breasts.
• About 40 percent of women in their 50s have dense breasts.
• About 25 percent of women aged 60 and older have dense breasts.

Your breasts are unique and can change over time. During pregnancy and breastfeeding, the dense tissue grows, and the breasts become denser and often larger. Breast density returns to what it was before the pregnancy about 2-3 months after breast-feeding is finished. With menopause, density tends to decrease, but doesn’t always. It is important for you to know your own breast density and what the limitations of mammography may be for your breast type.

Smaller breasts tend to be dense, and larger breasts are more often relatively fatty, but there is wide variation from person to person.

No. Breast pain or tenderness is not related to breast density. Breast pain that comes and goes is often due to hormonal fluctuations and is most common in the outer portions of the breasts. Breast pain alone is rarely due to cancer, though a painful lump can uncommonly be due to cancer and should be brought to the attention of a health provider. Benign (not cancerous) cysts, lymph nodes, and fibroadenomas, and other less common findings can cause tenderness. Very focal pain (one fingertip can point to it) that is persistent over several weeks should be brought to the attention of your health provider. Skin conditions such as shingles and underlying muscle soreness can be perceived as breast pain.

The radiologist who read your mammogram will send a report to your health care provider. Information about your density category (heterogeneously dense or extremely dense) is usually included in that report. The information may also be in the letter you receive after your mammogram. If it is not included, you can contact either the radiologist or your health care provider for the information.

Breasts tend to become less dense with age and menopause (see Figure below). If you lose a lot of weight, your breasts may appear more dense on a mammogram (as there is a loss of fat while the amount of dense tissue stays the same).

No. You would not know your breast density until you start having mammograms. Women at average risk for developing breast cancer should begin mammograms at age 40. If you have a family history of breast cancer, or do not know if you are at higher risk, talk to your health care provider about your risk factors and about what breast cancer screening plan is right for you.

If you are over the age of 40 and in good health, a mammogram every year (with 3D mammography/tomosynthesis, if available) is recommended. If your health care provider determines that you are at high risk of getting breast cancer, a yearly MRI may be recommended to begin by age 25 to 30, with yearly mammograms beginning at age 30.

Yes. “Dense breasts” are “normal.” About 40% of women over age 40 have dense breasts. However, while dense breast tissue may be normal, it can hide cancer on a mammogram and might make finding cancer more difficult, even if your mammogram was done with 3D/tomosynthesis.

A “normal,” “negative,” or “benign” mammogram does not necessarily mean cancer is not there. Women with dense breasts may have cancer detected after a “normal” or “negative” mammogram. Additional screening, for example with ultrasound or MRI, may find a cancer that is hidden on a mammogram. If your mammogram shows dense breasts, you should discuss whether you should have additional screening with your health care provider.

It is very important not to ignore a lump or any change in your breasts just because your recent mammogram was normal. This is especially important if your breasts are dense. While lumps are often cysts or areas of normal tissue, a lump may be cancer that is hidden within dense breast tissue on a mammogram.

A “normal,” “negative,” or “benign” mammogram does not necessarily mean there is no cancer. Ultrasound is often used to evaluate lumps.

Yes. Wherever possible, women with dense breasts should have a mammogram with 3D/tomosynthesis as 3D slightly increases cancer detection. However, in dense breasts, even 3D mammograms are less accurate in finding cancer than in fatty breasts. Mammograms do have some benefit.

Multiple studies have proven that the early detection of cancers by mammography reduces the risk of death due to breast cancer for women aged 40 to 74 years. While additional screening may be recommended for women with dense breasts and/or high risk for developing breast cancer, there are still some cancers and precancerous changes that will show on a mammogram better than on ultrasound or MRI (Figure below).

Mammography Shows Some Early Breast Cancers Not Seen on Ultrasound. Mammogram of a woman with heterogeneously dense breasts shows new grouped calcifications (white specks that are like salt crystals within yellow circles). These are difficult or impossible to see with ultrasound. Most calcifications seen on mammograms are not due to cancer but the area circled was early breast cancer (DCIS).

No. Ultrasound is not a replacement or substitute for mammography. Some breast cancers are only detected by 2D or 3D/tomosynthesis mammography, even in dense breasts.

Maybe not. Many studies show that women with prior breast cancers have an increased risk of second breast cancers. Some of these can be difficult to detect early with mammography.

Many studies show that ultrasound and/or MRI can improve early detection (even after 2D or 3D/mammography) in women previously treated for breast cancer.

The American College of Radiology now recommends an annual MRI in addition to mammography (either 2D or 3D/tomosynthesis) for the following women (provided the woman has not had a double/bilateral mastectomy):

• All women with a personal history of breast cancer and dense breasts.
• Women with any breast density diagnosed with breast cancer by age 50.

Ultrasound can supplement mammography for those who cannot undergo MRI. If screening MRI is performed, screening ultrasound is not needed.

Some sites now offer contrast-enhanced mammography. This may be an alternative to MRI, but is not widely available and research is ongoing.

If you have had a double/bilateral mastectomy and are otherwise in good health, follow-up should include a clinical exam by your health care provider and self-exams. It is important not to ignore any changes in your breasts.

You should begin screening at age 40. Though breast cancer is more common as women get older, it is still important to begin screening at 40 because:

• We screen for breast cancer to find it EARLY, when it is easier to treat and most survivable.
• Breast cancer is the number one cause of death in women aged 35 to 54 years.
• Deaths from breast cancer are reduced the most when screening starts at age 40. The most years of life are saved when screening starts at age 40.
• More than half of women in their 40s have dense breasts (heterogeneously dense or extremely dense). Dense breast tissue increases the risk for developing breast cancer and the consideration of additional screening after a mammogram.
• Women at “high risk” for breast cancer, most often because they have a disease-causing mutation (such as BRCA1 or BRCA2), should begin screening even younger – at least by age 30 and with the inclusion of an MRI.

WHAT ABOUT RECALLS AND FALSE POSITIVES (FALSE ALARMS)?

About 10% of women having a screening mammogram will be called back or “recalled” for extra views or tests to look at an area of the breast more closely. THIS IS EXPECTED. Additionally, it is much more common for women to be recalled after their very first mammogram as there is no prior mammogram for comparison. Among women called back, most (95%) do not have cancer. These are considered “false positives” or “false alarms” because the mammogram appears abnormal but no cancer is present.

Usually, extra mammogram pictures or an ultrasound can clear up a question raised on a mammogram. If a needle biopsy is needed, even that is a simple test, not much different from a dental filling. With the newer technique of 3D/tomosynthesis mammography, cancer is more easily seen and results in fewer callbacks for extra testing. Callbacks are more common in younger women (those in their 40s vs. those in the 50s) and are also more common in women with dense breasts than in women with fatty breasts.

IS IT COVERED?

• In the U.S., under the Affordable Care Act (Obamacare), insurance carriers are required to cover the full cost of a screening mammogram. Screening mammography is for women with no symptoms. If the screening is performed by 3D/tomosynthesis mammography, the full cost might not be covered by some insurance companies. It depends on what state you live in (click HERE to learn more) and what insurance you have.
• Insurance coverage for additional screening tests, such as ultrasound or MRI, also varies by state and by insurance company. Women should check with their insurance carriers to determine how additional tests will be covered. For women at high risk for breast cancer, most insurers will cover screening MRI (regardless of density), though a deductible/co-pay will typically apply, and pre-authorization may be needed.
• Diagnostic mammography is for women with a sign or symptom of breast cancer, such as a lump or nipple discharge. It is important to report any new symptom to your health care provider. A deductible/co-pay will usually apply for diagnostic mammography. But again, it depends on where you live and your insurance plan.

Mammograms are low-dose x-rays of the breast that have been used for screening since the 1980s. There are three different types of mammography:

• Film, 2-Dimensional, known as “analog” has been nearly eliminated in the United States.
• Digital, 2-Dimensional, known as “Full Field Digital Mammogram” (FFDM). Nearly all facilities in the United States have digital mammography.
• Digital, 3D/tomosynthesis, also referred to as “3-Dimensional” or “tomo.” It is a newer technology that is used in over half of the facilities in the United States.

The radiation exposure from a mammogram is minimal and has not been shown to cause any significant harm.

No, but they are different types of digital mammograms. While both are generated using computers, the 2D mammogram captures a 2-dimensional image. As an example, think of it as a photograph of the cover of a book. Even if the cover and pages were see-through, the words on each page of the book would have their letters jumbled on top of the words from other pages. The 3D mammogram captures images at multiple angles, which allows thin “slice” images to be created by the computer and viewed one at a time (similar to turning pages of a book and being able to read the words on each page).

The amount of radiation is about the same for 2D as for 3D mammograms. Some facilities still perform a standard 2D in addition to the 3D, so the total dose would be about double that of a standard 2D mammogram. Other facilities can create what is called a “synthetic 2D mammogram,” so only the 3D images are taken. Using that approach, the dose is about the same as a standard 2D mammogram.

A 2D mammogram finds about 2-7 cancers for every 1,000 women who have a mammogram. For most women, another 1-2 cancers will be found per 1,000 women when 3D/tomosynthesis is added to a standard mammogram. 3D mammograms have not been shown to increase cancer detection in extremely dense breasts.

A cancer “hidden” on a 2D mammogram, could still be hidden on a 3D mammogram.

Yes. In the U.S., to legally perform mammography, a facility must be certified and recognized by the U.S. Food and Drug Administration (FDA) which maintains a Mammography Facility Database. Click Here for the list of FDA recognized accredited facilities.

An imaging center may receive further accreditation through the American College of Radiology (ACR). The ACR’s accreditation program, which designates Diagnostic Imaging Centers of Excellence^®, assesses imaging centers for a number of qualifications (e.g. personnel, policies, equipment, image quality and patient care). Such centers also must have ACR accreditation for stereotactic breast biopsy, ultrasound-guided breast biopsy, and breast MRI. Click Here for a list of ACR Diagnostic Imaging Centers of Excellence.

Ultrasound and MRI are the most common supplemental screening options after a normal mammogram. Depending on your age, your risk level (as determined by a health care provider), and your breast density, additional screening (with ultrasound or MRI), may be recommended in addition to your routine 2D or 3D/tomosynthesis mammogram. The extra testing after your mammogram may find more cancers than mammography alone (see Table below), though most women being screened will not have breast cancer. Some centers are evaluating contrast-enhanced mammography as an alternative to MRI.

Extra testing, known as “supplemental screening,” is different than being “called back.” It is normal for any screening test (mammogram or supplemental) to find things that may need to be looked at more closely. This is known as a callback (or “recall”) appointment and additional diagnostic imaging will be used. While some of these additional findings might be cancers, the vast majority will not be cancer (known as a “false positive”). The only way to determine if something is cancerous is through additional imaging and sometimes biopsy.

Cancer Find Rates When Ultrasound or MRI is Added to Mammography

Yes, you may still need more screening if you have dense breasts and/or are at high risk. Ultrasound or MRI might find cancers even after “normal” 3D mammograms. This has been shown in several large studies. It is still important to have your mammogram, as mammograms do find some cancers that ultrasound or MRI may not find. The combination of tests finds the most cancers. If you are recommended to have a screening MRI because of risk factors, you will still need to have an MRI even if you have a 3D/tomosynthesis mammogram. But if you have an MRI, there is no need to also have a screening ultrasound.

Your routine annual mammogram should be scheduled as a “screening” mammogram. Screening mammograms are for women with no signs or symptoms of breast cancer, whether you have dense breasts or not. Screening mammograms are fully covered by insurance under the Affordable Care Act for women over the age of 40 in the United States, and may be covered for younger women, if recommended by her physician and depending on the insurance policy.

“Diagnostic” mammograms are used when there are signs and symptoms of breast cancer such as a lump, bloody or spontaneous clear nipple discharge, and/or skin or nipple retraction. Diagnostic mammography is typically covered by insurance, but is subject to deductible and copay.

You should discuss this with your health care provider or breast imager because, as you get older, your personal risk factors and the benefits and types of additional screening recommended may change. It is therefore important to review your risk factors every year or two with your health care provider to determine what screening plan is best for you.

Molecular Breast Imaging (MBI) and Breast Specific Gamma Imaging (BSGI) are specialized nuclear medicine procedures that can detect cancers hidden within dense breast tissue on a mammogram; these imaging procedures are not generally recommended for screening.

These tests require an injection of a small amount of radioactive material, which circulates throughout the body. Breast cancers take up the radiotracer more than normal cells do. This allows the cancer to be seen on special cameras. An advantage of these tests is that they are not affected by breast density. A disadvantage is that the radiation from these tests is to the whole body, unlike mammography, where only the breasts receive radiation (in a very small amount), and unlike ultrasound or MRI, where there is no radiation at all.

There are ongoing studies to see if the radiation dose from these tests can be lowered so that they can be widely used for screening. However, for now, MBI and BSGI are most often used as diagnostic tools.

A diagnostic tool is one which helps diagnose cancer once a symptom appears (for example, a lump that can be felt), or when there is a vague area of possible concern found after additional mammogram views and ultrasound. MBI or BSGI can also be helpful for some women who need, but cannot have an MRI. These tests are not used in women who are pregnant.

No. Thermography is a technique that uses infrared technology to detect both heat and blood flow patterns very near the skin’s surface, and some large cancers can be seen this way. However, thermography has a high “false negative” rate (when a test result indicates “no cancer” even though cancer is actually present), especially for small breast cancers. It can also have “false positives” (when a test result indicates cancer may be present when it is not).

According to the FDA, “There is no valid scientific data to demonstrate that thermography devices, when used on their own or with another diagnostic test, are an effective screening tool for any medical condition including the early detection of breast cancer or other diseases and health conditions.” Thermography is not an accurate test and is not recommended for screening.

The answer is maybe. It depends on the type of screening, your insurance, your risk factors, and whether there is a law in effect requiring insurance coverage for additional screening in your state. Check with your insurance carrier before having additional screening. For information about insurance coverage within your state, visit the Legislation Information tab’s interactive map.

Diet and exercise do not directly alter breast density. Substantial weight loss or gain can affect breast density. If you gain weight, there will be more fat (non-dense tissue) in the breasts and they may be visibly less dense on a mammogram. If you lose weight, you will lose fat from your breasts and the breasts may appear denser on a mammogram. So, while not related to diet or exercise, breast density does relate to overall body fat. Your body mass index (BMI) is an estimate of your body fat.

BMI uses your height and weight to estimate body fat. BMI and breast density are both separate and independent risk factors for breast cancer. Before menopause, low BMI (being thin) increases the risk of breast cancer. After menopause, weight gain and high BMI increase the risk of breast cancer (being thin decreases the risk of breast cancer). Please speak to your doctor about the optimal BMI for you.

It can. While exercise can decrease the amount of fat in the breast, the glandular or dense breast tissue is not affected by exercise. So, if you lose a lot of weight due to exercise, the breasts can appear more dense due to loss of fat because the amount of fat decreases while the amount of dense tissue stays the same.

While exercise does not decrease the actual amount of dense tissue in the breasts, it does decrease the overall risk of developing breast cancer.

Yes. An increase in breast density is often seen in women taking combined estrogen and progesterone hormone replacement therapy (HRT), and sometimes in women using oral low-dose estrogen, vaginal estrogen, or transdermal estrogen treatment. The increase in density is often apparent within months of beginning hormone therapy. Risk of breast cancer also increases in women taking combined hormone therapy.

Maybe. In some women, tamoxifen does decrease breast density. Tamoxifen works by blocking estrogen in the breast. Tamoxifen is sometimes prescribed to decrease the chance that cancer will return in women who have had estrogen receptor positive (ER-positive) breast cancer. It may also be prescribed to reduce the risk of developing breast cancer in women who have had prior atypical biopsy or those at higher risk for breast cancer for other reasons.

Early studies suggest that only those women who experience a decrease in their breast density while taking tamoxifen will experience a decreased risk of getting an ER-positive cancer. The extent of change in breast density due to tamoxifen is small.

It is important to be aware that tamoxifen therapy has risks. Tamoxifen increases a woman’s risk of blood clots and of cancer of the lining of the uterus.

Maybe. Aromatase inhibitors (AIs) block your body’s own production of estrogen. AIs are prescribed for postmenopausal women who have had estrogen receptor positive (ER-positive) breast cancer. One study of breast cancer survivors taking AIs showed that those survivors who experienced a decrease in their breast density had a lower risk of recurrence than women who did not experience a decrease in breast density.

Yes. If you have a history of breast cancer and have dense breasts, there is a greater risk of developing cancer in the opposite breast (known as contralateral breast cancer). The good news is that this risk can be reduced with treatment. Tamoxifen (premenopause) or aromatase inhibitors (postmenopause) are medications given to women with “ER-positive” breast cancer to reduce risk of developing future breast cancer. That reduced risk is only seen if your breast density is reduced by at least 10% (when measured by special software). Knowing whether or not your breast density was affected by the medication may help you decide whether or not to continue the medication.

No. Having “lumpy” or fibrocystic breasts does not always mean you have dense breasts. The way to tell if you have dense breasts is with a mammogram. Your doctor cannot tell if your breasts are dense by a physical exam.

Breasts (of any density category) can feel lumpy as the ligaments which support the breast tissue can surround fat lobules and make them feel like soft grapes. Remember, fibrocystic change is a benign (non-cancerous) condition that is more common when women are young. Fibrocystic changes usually decrease after menopause. Fibrocystic breasts can appear dense due to cysts and/or areas of fibrosis (which resemble scar tissue).

No. Normal male breasts are mostly fatty. However, it is important to remember that men do get breast cancer. Men can develop breast tissue (known as gynecomastia) as they age or as a side effect of some medicines; however, gynecomastia is nothing to worry about. Sometimes, a mammogram is performed in men to evaluate a lump that may be due to gynecomastia or breast cancer.

Breast density is at least partially inherited. If your mother or sister has dense breast tissue, it’s more likely you will too.

Yes. Changes in the breast during breastfeeding do reduce the accuracy of mammography, but mammograms are still recommended. Depending on your individual risk factors, ultrasound or MRI may sometimes be added to mammography for additional screening. Breastfeeding also affects the appearance of the breasts on ultrasound and MRI.

There have been conflicting studies on whether Black women have denser breasts. One study indicated they do not, while a more recent study indicated they do have denser breasts.

Generally, Asian women do have denser breasts than women of other races.

BRCA gene mutations and dense breasts are both risk factors for breast cancer. However, BRCA1 or BRCA2 mutations are associated with a much higher risk for developing breast cancer than is the risk from having dense breasts.

Because BRCA gene carriers are more likely to develop breast cancer at a younger age, they typically have breast MRI as part of their routine screening. Screening should also start earlier, with MRI beginning at age 25 and also mammography starting at age 30. The addition of MRI screening for women with BRCA mutations is recommended whether or not they have dense breasts.