• Breast density is associated with an increased risk of breast cancer and is present in about 50% of adult women.
• Breasts have three types of tissue: fatty tissue, glandular tissue, and fibrous tissue. Breast density is defined by the ratio of fatty breast tissue to dense breast tissue (glandular + fibrous tissue).
• Doctors use a mammogram to compare how much fatty tissue there is to the total amount of fibroglandular tissue (glandular plus fibrous tissue) when assessing whether a person has dense or non-dense breasts.

A mammogram is an X-ray of the breasts and is the most effective way of detecting breast cancer at an early stage before it can be felt as a lump. Mammograms can also detect what is called mammographic breast density, aka "dense breasts."

There are two critical factors a person should know about breast density:

1. Dense breasts are associated with a higher lifetime risk of breast cancer.
2. Dense breasts can reduce the sensitivity of mammograms to detect breast cancer, and therefore make it more difficult to make a diagnosis.

This article discusses how to tell if you have dense breasts and what that means for your overall health.

What are dense breasts?

Dense breasts are defined by the ratio of fatty breast tissue to dense breast tissue. For reference, breasts are comprised of three types of tissue:

• Fatty (adipose) tissue appears as black on the mammogram just like the air in the lungs appears on a chest X-ray.
• Glandular tissue (parenchymal) Includes the lobes that produce milk and the ducts that carry milk toward the nipple. This tissue appears white on a mammogram.
• Fibrous tissue provides the infrastructure that surrounds the fibrous and fatty tissues and also appears white on the mammogram.

The proportions of these three tissue types are unique to a given individual. To assess whether a person has dense or non-dense breasts, doctors use a mammogram to compare how much fatty tissue there is to the total amount of fibroglandular tissue (glandular plus fibrous tissue). Based on those proportions, experts have divide women's breast density into four categories that are designated on all mammogram reports:

• Fatty, less than 25% dense tissue (10% of women)
• Scattered fibro glandular tissue, 25-50% dense (40% of women)
• Heterogeneously dense tissue, 50-75% dense (40% of women)
• Extremely dense, 75-100% dense tissue (10% of women)

While the first two categories are considered non-dense, the second two categories are considered dense breasts. Therefore, about 50% of women fall into this characterization, which comes with increased cancer risk. Other risk factors that may increase risk of breast cancer independent of breast density include:

• Genes (BRCA) or family history of breast or ovarian cancer.
• Giving birth after the age of 30.
• Risk increases with increasing age after 40.
• Hormone replacement therapy
• High BMI

"Women with dense breasts do have a higher risk for breast cancer and should keep up to date with regular mammograms and go for regular breast exams with their gynecologist or primary care physician," says Soma Mandal, MD, women's health specialist and internist with Summit Medical Group in New Jersey.

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.

• Breast ultrasound is effective in distinguishing between cysts and masses that need to be biopsied to exclude breast cancer.
• Breast MRI can give more information on breast tissue. It is the undisputed, most sensitive test for the detection of breast cancer.
• 3-D mammogram, formally known as breast tomosynthesis, provides a more thorough picture of breast tissue, may reduce the need for subsequent tests, and has been proven to improve detection in dense breasts.
• Molecular breast imaging (MBI) is very accurate at detecting cancers but exposes a patient to more radiation than other screening options. It is only recommended for women with a very high risk of breast cancer, for instance, those with a genetic predisposition, Mandal says.

How often should I get a mammogram if I have dense breasts?

Multiple societies have different guidelines that include beginning screening at the age of 40 with no upper age limit. The different guidelines reflect economics and politics of costs to the general society.

However, all societies acknowledge that screening mammography reduces breast cancer mortality in all age groups 40 and above. For more information, you can visit these societies' websites:

• American College of Radiology
• National Comprehensive Cancer Network
• American Society of Breast Surgeons
• American Cancer Society

By the age of 40, you should at least consult with your doctor about the option of a mammogram and by age 45, you should start scheduling annual mammograms.

Ideally, your annual mammograms should be done at the same place, Mandal says. That way, the radiologist can compare your past mammograms to the current results and more easily detect any changes that could indicate cancer.

After the age of 55, women should get bi-annual mammograms, Mandal says.

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.

Insider's takeaway

Having dense breasts - a higher concentration of fibroglandular tissue compared to fatty tissue - can increase your risk for breast cancer by up to five times.

Although it's recommended that all women regularly conduct self-checks for breast cancer, dense breasts cannot be detected through touch - even by a trained doctor. Only a mammogram can tell you if you have dense breasts.

Mandal recommends that women with dense breasts talk with their doctor and take breast density into account along with other risk factors to determine an individual screening plan.

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