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Why Do Dense Breasts Need More Mammograms?

Why Do Dense Breasts Need More Mammograms?
After you go in for your yearly mammogram, you figure your job is done. Then the results come back and your doctor says that you have “dense breasts.” They want to perform another mammogram and other tests, too. Why? Are dense breasts dangerous?

Every year in the United States, doctors report approximately 240,000 new breast cancers in women. Each year, more than 40,000 women die from breast cancer.

You want to minimize your risk for early death from breast cancer, so you always make sure to get yearly mammograms. Mammograms can identify breast cancer in its earliest, most treatable stages, which dramatically increases your chances of long-term survival.

So, when your doctor tells you that your mammogram shows that you have a condition called “dense breasts,” and recommends something called a “diagnostic mammogram,” you’re understandably concerned. What are dense breasts? Are they a cancer risk? And why do you need more tests to find out if you’re cancer-free or not?


Our expert doctors at Mass Medical Imaging in Lake Forest, Illinois, Joseph Calandra, MD and Karen Mass, MD, recommend regular screening mammograms starting at age 40. However, if you have dense breasts, you may need a diagnostic mammogram and other tests to ensure that you’re cancer free or to catch any possible cancers as soon as possible.

If you’re a woman who’s been told you have dense breasts, you may wonder what that means and why you need more tests. We created this brief guide to help answer your questions.

What are dense breasts?

First of all, dense breasts are very common and are considered a normal finding on a mammogram. In fact, approximately half of all women who get mammograms at age 40 or beyond have dense breasts.


Dense breasts are breasts that are composed of more glandular and supportive tissues rather than fatty tissue. On a mammogram, fatty tissue appears black and translucent. Dense, supportive tissue, however, appears white. Because cancer cells and tumors also appear white on mammograms, dense tissue makes it more difficult to detect abnormalities.

You’re more likely to have dense breast tissue if you have a low BMI or use hormone therapy after menopause. You’re also more likely to have dense breast tissue if you didn’t give birth to children. Or you may have inherited your dense breasts.

Breasts are classified by their degree of density on a mammogram:

Category A

Breasts are almost entirely composed of fatty breast tissue. Only 10% of women fall into category A. 

Category B

Areas of dense glandular and fibrous tissue (i.e., white on mammogram) are scattered in fatty tissue. About 40% of women fall into category B.

Category C

Another 40% of women are found to have heterogeneously dense breast tissue. That means there are many areas of dense glandular and fibrous connective tissue, with just a few areas of fatty tissue. 

Category D

About 10% of women have extremely dense breast tissue. Their breasts are almost entirely composed of glandular and fibrous connective tissue, with very little fat.

If you fall into categories C or D, you’re considered to have dense breasts and should have a diagnostic mammogram as well as, possibly, other tests.

Do dense breasts increase my risk for breast cancer?

Dense breasts make it harder to detect tumors on mammograms, because the tumors and the density both appear white. The denseness also makes it hard to see what’s underneath a portion of breast tissue. To get a better sense of the health of your breasts, your doctor needs to take a second and closer look at areas of concern.

Independent of the difficulty of detecting cancer with dense breasts on mammograms, however, having dense breasts does increase your risk for breast cancer. If you’re in category 4, you’re 4-6 times more likely to get breast cancer than a woman in category 1 is. Glandular tissue is more likely to develop cancerous cells than fatty tissue is.

How do extra mammograms help?

If you have dense breasts, a single mammogram can’t look closely enough at the densest areas for us to distinguish cancer from breast tissue. A second mammogram, sometimes called a diagnostic mammogram, helps us look at areas of concern, such as those where the tissue is particularly dense.

Depending on your situation, we may also recommend other tests that give us a closer and clearer look inside your breasts, including:

  • Breast tomosynthesis
  • Breast ultrasound
  • Breast MRI

If you have dense breasts, schedule a follow-up mammogram or other tests today calling our friendly team or using our online appointment form.