McLeod Radiologist Explains Breast Tissue Density


Dr. W. Shawn Conwell, McLeod Radiologist

What is dense breast tissue, and why does this matter to ME?

Breast tissue density is essentially an observation of how much fat versus fibro-glandular tissue (NORMAL tissue) is in the breast. Fat appears black on a mammogram, while normal tissue appears white on a mammogram. Most forms of breast cancers are also white on a mammogram.

If your breast is composed of almost entirely fat (black), and a white cancer shows up, this is very easy to see on a mammogram – kind of like a star in the night sky.

However, if your breasts are dense, the mammogram has lots of white (tissue) and no black (fat).  Finding a cancer in this circumstance is like searching for a polar bear in a snowstorm; it is extremely difficult to see a cancer in dense breasts. In fact, about 50 percent of cancers in extremely dense breasts are completely invisible on a mammogram.

We classify breast tissue according to four categories – from almost entirely fatty to extremely dense:

a. The breasts are almost entirely fatty
b. There are scattered areas of fibro-glandular densities
c. The breasts are heterogeneously dense, which may obscure small masses
d. The breasts are extremely dense, which lowers the sensitivity of mammography

Approximately 40 percent of the screening age population, age 40 and older, has dense breast tissue (categories c and d above).

Dense breast tissue may also be a risk factor for developing breast cancer, similar to a first-degree relative (mother, sister, etc.). However, this remains an area of active research.

Breast tissue density can only be accurately determined by a mammogram. Younger women tend to have denser breasts, but there are many older women who also have this composition.  Similarly, some young women have more fatty breasts. Density is not related to breast size, shape, or texture. You must get a mammogram to know if you have dense breasts.

According to the American Cancer Society, 75 to 80 percent of discovered breast cancers occur in women who have no family history and no other risk factors. Radiologists have long been aware that mammography is not optimally suited for imaging dense breasts. Recent research, however, has established the ability of breast ultrasound, when used as a supplement to screening mammography in women with dense breasts, to increase cancer detection rates by nearly 60 percent.

In addition to breast ultrasound, the use of breast tomography (3D mammography) has also been shown to increase the cancer detection rates in all women, including those with dense breasts.  The use of breast tomography will also reduce unnecessary call back examinations, cutting the false positive rate of screening mammograms nearly in half.

We are deploying both of these imaging tools at McLeod Regional Medical Center in the coming months.

Hope’s Law
With only a single objection, “Hope’s Law” passed the South Carolina legislature in May 2016.

Hope’s Law adds South Carolina to the 35 other states now requiring breast tissue density notification to patients. Federal law, specifically the Mammography Quality Standards Act, requires mammography providers to notify patients directly, not just through their doctor, the results of their mammogram.

South Carolina’s Hope’s Law now requires mammography providers to also notify all patients of their breast tissue density in “conspicuous language.”  “When applicable,” the letter should include the following:

“Your mammogram shows that your breast tissue is dense. Dense tissue is common and is not abnormal. However, dense breast tissue can make it harder to evaluate the results of your mammogram and may also be associated with an increased risk of breast cancer. This information about the results of your mammogram is given to you to raise your awareness and to inform your conversations with your doctor. Together, you can decide which screening options are right for you. A report of your results was sent to your physician.”

Furthermore, in order to ensure that accurate and up-to-date information was given to patients, radiologists worked to include in the law the unique recommendation of this third provision:

“Consumer or patient information available from the American College of Radiology about breast density and mammogram reports must be included” in the notification.

A consensus statement recognized by the American College of Radiology and collaboratively produced with the Society of Breast Imaging can be found at by clicking on “Tools and Resources.” This downloadable brochure is available in both English and Spanish.

Additionally, more comprehensive information can be found at

These resources provide accurate, scientific, and consensus-based information on breast tissue density.

If you have any further questions about these services, please feel free to call the McLeod Breast Imaging Center at (843) 777-6317.