Breasts are considered dense if they primarily consist of fibrous or glandular tissue and little fatty tissue. Much like lumps, both benign and cancerous, dense breast tissue appears white on a mammogram, making it difficult to distinguish normal tissue from cancer. Current research suggests that women with dense breasts are at increased risk for breast cancer compared to women with fatty breasts.
When reading your mammogram, a radiologist assigns it to one of four categories of breast density. 10% of women in the U.S. have extremely dense breasts while another 10% have almost entirely fatty breasts. The remaining 80% of women are classified into one of the two middle categories. As a woman ages, her breasts may gradually become more fatty.
If you are classified as having dense breasts, it is recommended that you continue to have an annual mammogram. Although dense breast tissue makes it more difficult to see, many cancers continue to be found using the screening tool of mammography. For patients who have additional risk factors for breast cancer, ultrasound and MRI exams are available in addition to mammogram to aid in diagnosis. If you have any concerns, please discuss with your doctor which exams are right for you. For more information about breast density, please visit AreYouDense.org.
Regardless of your breast density, we recommend an annual mammogram starting at age 40.
Effective August 1, 2014, a new law by the Minnesota State Legislature required all Minnesota mammography facilities to report breast density to patients with dense breasts. This law was enacted for three reasons:
- Dense breasts slightly decrease the ability of mammography to find breast cancer.
- Dense breasts slightly increase the risk of breast cancer.
- Patients may want to know about other ways to screen for breast cancer if they have dense breasts.
Why do dense breasts decrease the ability to find breast cancer?
Cancer on mammography is a white spot or white dots. A dense breast has a white background. Finding a white spot or white dots is harder on a white background than on a gray background. This ability to find the breast cancer decreases by 10 to 20% in a dense breast utilizing digital mammography.
How much do dense breasts increase my risk for breast cancer?
For most women, breast density is not a major cancer risk factor. There are four categories of breast density used by radiologists. Categories A and B are considered not dense. Categories C and D are considered dense.
A. Almost entirely fatty
B. Scattered areas of fibroglandular density
C. Heterogeneously dense breasts increase your risk of breast cancer 1.2 times a normal risk. 40% of women have heterogeneously dense breasts.
D. Extremely dense breasts double your risk of breast cancer. While this relative risk may seem high, the actual risk is still low. 10% of women have extremely dense breasts.
Other risk factors for breast cancer not related to breast density include age, family history, early menstruation, diet, alcohol use, obesity, lack of physical activity, radiation to the chest and hormone replacement therapy. A reference for more information is: nationalbreastcancer.org.
Is mammography still worthwhile in women with dense breasts?
Yes. The screening recommendations for women with dense breasts are the same as other women. Also, there are some breast cancers that are best seen with mammography.
What other methods are available?
There are three other screening options available, the first two of which are performed at The Breast Center of Suburban Imaging.
- Screening Breast Ultrasound can detect slightly more cancers. However, it has a high rate of adding more tests or biopsies that turn out to be normal. Only 5% of lesions detected with breast ultrasound turn out to be cancer. Screening breast ultrasound is usually an out-of-pocket expense.
- Screening Breast MRI can increase the rate of cancer detection.
• It is recommended by the American Cancer Society for women who are at very high risk (>20% lifetime risk).
• For those at intermediate risk (such as a personal history of breast cancer, or a biopsy diagnosis of atypia) there aren't specific recommendations, and a shared decision-making approach is recommended.
• For women at a relatively normal risk, breast MRI is not recommended. For intermediate and normal risk patients, breast MRI may be an out-of-pocket expense.
- Breast tomosynthesis, (3D mammography) can increase the detection rate of breast cancer, particularly in women with extremely dense breasts. It may require additional radiation, (still within the federal guidelines for screening) but it also decreases the number of women called back for more imaging.
This information about the results of your mammogram is given to you to raise your awareness about breast density. Together, you and your health care provider can decide which screening options are right for you based on your mammogram results, individual risk factors, and physical examination. Additional references on breast density include breastdensity.info, and information at cancer.org.