A new law takes effect in Georgia on July 1, 2019 requiring facilities that perform mammography to add specific verbiage to lay-language results letters for patients with dense breast tissue. This verbiage will alert patients that they have dense breast tissue, which, while not abnormal, may mask cancers on mammography and may also increase the risk of breast cancer. It will also advise them to speak with their healthcare provider about whether supplemental screening may be appropriate based on their individual level of risk.
As healthcare providers, we must be prepared to respond to these inquiries.
Breast density is a measure of the proportion of fibroglandular tissue to fatty tissue. It is determined based on the appearance of the tissue on a mammogram, and does not relate to how a breast looks or feels on physical exam. When interpreting mammograms, radiologists must classify breast tissue into one of four density categories – “almost entirely fatty”, “scattered areas of fibroglandular density”, “heterogeneously dense”, or “extremely dense”. The latter two categories are considered “dense”. About 50% of US women fall into one of these two “dense” categories.
Dense breast tissue can be clinically significant for two reasons. First, it can mask a cancer on a mammogram. Fibroglandular tissue looks white on mammography while fatty tissue appears dark gray. Cancers also look white on mammography and may not stand out against a background of dense tissue. Second, research has shown that, independent of family history and other risks, having dense breast tissue can be a risk factor for breast cancer. The increase is about 1.2-2 times for dense breasts overall compared to average, but the difference between “almost entirely fatty” and “extremely dense” is about four-fold.
Having dense breast tissue does not mean that a woman should forego mammography. Mammography is the only test proven to save lives from breast cancer, and some of the earliest cancers are only visible on mammography. Breast tomosynthesis (also known as 3D mammography) has further improved the performance of mammography. In large studies, tomosynthesis has been shown to find 40% more cancers than 2D mammography alone and a decrease in the number of patients recalled for additional imaging by about 15%.
However, even with tomosynthesis, some cancers can be masked on mammography. Women with dense tissue may wish to consider supplemental screening, especially if they have additional risk factors.
Large studies comparing supplemental screening with ultrasound and MRI have consistently shown that, while both of these tests can find some additional cancers, MRI finds significantly more. The highest cancer detection rate is found with the combination of mammography and MRI. Adding ultrasound to this combination does not increase cancer detection rate and results in a very high false positive rate.
The American College of Radiology, American Cancer Society, and other health organizations recommend annual MRI in addition to mammography for high-risk women (>20% lifetime risk of breast cancer), regardless of breast density. For women with lower risk seeking supplemental screening, “abbreviated” or “fast” breast MRI can provide a quicker, less costly option, while maintaining the benefits of MRI. For women with increased risk or dense tissue who have a medical contraindication to MRI, screening ultrasound may be considered.
Dr. Lynn Baxter is the director of breast imaging at Northside Hospital and Northside Radiology Associates.