Usually the answer is yes, though age and other medical conditions will change a patient’s personal risk and benefit considerations and therefore screening recommendations may change from one year to the next. Technology is changing and guidelines also evolve which influence recommendations.
No. Fat content in what you eat and exercise do not directly change breast density. But if you lose or gain a lot of weight, your breasts can look more or less dense on your mammogram – though the amount of dense tissue will stay the same. This is because if you gain weight, there will be more fatty tissue (non-dense) in your breasts. If you lose weight, you will lose fatty tissue from your breasts. So, although the foods you eat and exercising do not change your breast density, your overall body fat can affect your breast density.
For more information, see Q+A, “Will my breasts always be dense?”
Molecular Breast Imaging (MBI) is a specialized nuclear medicine breast imaging technique that requires intravenous injection of a radiopharmaceutical, typically 99mTc-sestamibi. Sestamibi has been in common use as a tracer for nuclear cardiology studies for over 30 years and has an extremely low risk of adverse reactions and no contraindications. Low-dose molecular breast imaging has been used with excellent results by The Mayo Clinic and a few other centers for screening women with dense breasts, showing another 7 to 8 cancers after a normal mammogram for every thousand women screened [1-3].
Breast Specific Gamma Imaging (BSGI) is also a nuclear medicine breast imaging technique that requires intravenous injection of a radioactive agent. Due to differences in equipment, it requires a higher radiation dose than MBI and is not recommended for routine screening.
MBI or BSGI can be useful diagnostic tools in women who have dense breasts and symptoms such as a lump or vague abnormality on mammography that in rare cases cannot be sorted out with additional views or ultrasound. MBI or BSGI can also be helpful for some women who need but cannot have an MRI. As of the most recent review in 2017, the American College of Radiology Practice Parameter for Molecular Breast Imaging  suggests MBI is a potential option for supplemental screening in high-risk women and those with dense breasts who cannot undergo MRI, but it is usually not indicated, as the technique involves ionizing radiation to the whole body with attendant risk of potentially inducing cancer . These tests are never used in women who are pregnant.
The radiation exposure from low-dose MBI, performed with a delivered dose of 6 to 8 mCi 99mTc-sestamibi, is higher than that from a mammogram. Further, mammography delivers radiation to the breast only, while MBI and BSGI deliver radiation to the whole body. In order to compare radiation doses from these different types of exams, a standard calculation called “effective radiation dose” is used, which takes into account which body parts are exposed to radiation by a given test and how sensitive every exposed organ is to radiation. Effective dose has units of milli-Sieverts (mSv). The effective dose of mammography is about 0.5 mSv and the effective dose from a low-dose MBI is about 1.8 to 2.4 mSv. BSGI has a higher effective dose of between 4.5 and 9 mSv. For comparison, the radiation dose received from normal daily life is between 2 and 10 mSv per year, depending on where you live. Below effective doses of 50 mSv, health risks from radiation are “too low to be detectable and may be nonexistent,” according to national and international radiation physics experts [6-8].
Chart 1. Graph compares the effective radiation dose (mSv) to the whole body from common medical exams (CT = computed tomography; PET = positron emission tomography). Annual background radiation is between 2 and 10 mSv (greater at higher elevations such as Denver, CO). The annual limit for radiation workers is 50 mSv, below which it is considered unlikely to observe cancers caused by radiation exposure. Any risk from radiation is greater in younger individuals, especially those under the age of 30, and radiation exposure should always be minimized (except when undergoing treatment of a known cancer).
Yes. An increase in breast density is often seen in patients taking combined estrogen and progesterone hormone supplements (also called hormone replacement therapy, or HRT). This includes women and transgender patients using oral low-dose estrogen, vaginal estrogen, or transdermal estrogen treatment.
The increase in breast density often begins within a few months of starting hormone supplements. Hormones stimulate the growth of both normal and abnormal breast tissue. An increase in normal breast tissue increases breast density. Cancers that have estrogen receptors will also develop or grow as a result of hormone supplements. If you stop taking hormone supplements, your breast density and cancer risk decrease within months.
No. 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 a non-invasive technique that uses infrared technology to detect both heat and blood flow patterns very near the skin’s surface. Although some large cancers can be seen, these are usually palpable and so thermography adds little. Thermography has a high “false negative” rate (when a test result indicates “no cancer” – though cancer is actually present), especially for small breast cancers, so it does not play a role in screening asymptomatic women. Thermography also has a high rate of “indeterminate” findings, which on additional diagnostic evaluation (mammography, ultrasound, MRI, follow-up observation, etc.) indicate no cancer is found. These often prompt a recommendation for short interval follow-up, which creates anxiety and additional cost to the woman.
Yes. If you have dense breasts and have had breast cancer, there is a greater chance of developing cancer in the opposite breast (known as contralateral breast cancer). The good news is that this risk can be reduced with medications.
The answer is essentially “yes”. At the population level, there is a tendency for slight decrease in breast density each year, and this tends to be more abrupt in the few years around menopause. One study  showed that only 7% of women who were considered not dense one year were classified as “dense” the following year; similarly 6% of women considered “dense” one year were classified as not dense the following year. For 87% of women, there was no change from one year to the next. Any difference that might affect the decision for supplemental screening would be between women considered to have heterogeneously dense or scattered fibroglandular density one year or the other, and radiologists may differ in this assessment even when there is no true change in the breasts. In a patient with breast density near the threshold, there are likely to be areas in the breast where cancer could be masked: it is not unreasonable to have had supplemental screening even if one’s breasts turn out to be slightly less dense this year.
No. Having “lumpy” or fibrocystic breasts is different than having dense breasts, but some women have both.
Normal breast tissue can feel lumpy whether it is fatty or dense. Cysts are common and noncancerous and sometimes are large enough to be noticed as a lump. Having dense breasts has nothing to do with the way your breasts look or feel. The doctor who reviews your mammogram determines whether you have dense breasts after looking closely at images from your mammogram.
Dietary fat intake has little to do with breast density; however, it does relate to increased body mass index (BMI). BMI is a measure of body fat based on height and weight, and there is more fatty breast tissue in women with higher BMI. Higher BMI reduces the percent of density but might not reduce the total amount of dense tissue. BMI and breast density are both separate risk factors for breast cancer. Before menopause, low BMI [1, 2] increases the risk of breast cancer. After menopause, weight gain and increasing BMI increase the risk of breast cancer.
No. Normal male breasts do not contain dense tissue.
Sometimes men’s breasts do grow and look more like female breasts (known as gynecomastia). This can happen as men age or can be caused by some medicines.
It is important to remember that men can also get breast cancer. A mammogram can be done in men to check a lump.
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 a woman loses a lot of weight due to exercise, her breasts can appear more dense due to loss of fat (the amount of fat decreases while the amount of dense tissue remains 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 .
An increase in mammographic density is much more common among women taking continuous combined (estrogen plus progesterone) hormonal therapy (seen in 21-43% of such women) than for those using oral low-dose estrogen (6%) or transdermal (2%) estrogen treatment. The increase in density is often apparent at the first visit after starting hormonal therapy. Due to the increased risk of breast cancer in women taking combined hormonal therapy, recommendations are that use not extend beyond 3 to 5 years [1-5].
Tamoxifen blocks the estrogen receptor in breast cells and in breast cancer cells which express the estrogen receptor. Tamoxifen may be recommended to reduce the risk of developing breast cancer in women who have had prior atypical biopsies. Tamoxifen is also prescribed for women who have had breast cancer that expresses estrogen receptors to decrease recurrence. One study  found that when breast density is carefully measured by computer software, women whose breasts became at least 10% less dense while taking tamoxifen had a 63% reduction in risk of developing breast cancer – whereas those whose breast density did not change did not see a decrease in their risk. Several similar studies [2, 3] in women who have had breast cancer showed that only women whose breast density decreased on tamoxifen had decreased risk of recurrence. Tamoxifen also carries about a 3% risk of blood clots (which could result in pulmonary embolism or stroke) and a smaller risk of endometrial cancer (if the woman still has her uterus).
If a woman is on hormone therapy for menopausal symptoms, her breast density may decrease if she stops taking hormone supplements.
Aromatase inhibitors block the body’s own production of estrogen and are prescribed for postmenopausal women who have had breast cancer where the tumor cells express receptors for estrogen. One study [1, 2] looked at women who have had breast cancer. When breast density is carefully measured by computer software, women who experienced a decrease in breast density while taking tamoxifen or aromatase inhibitors had a lower risk of recurrence than women who did not experience a decrease in breast density.