Many of my patients have noticed and asked about a recent addition to their mammogram results letter – a comment regarding the density of their breast tissue.
What is breast density?
It’s a proportional measure of the different types of tissue that make up breasts. Glandular and connective tissue absorb more radiation and show up white, whereas fatty tissue is dark. The ratio of white to dark determines breast density. For consistency, a scale of 1-4 was created (the BiRADS scale) to describe the density of breasts on mammogram reports.
A lot of women – about 50% – have dense breast tissue: 40% moderately dense and 10% extremely dense. Increased density obscures mammogram imaging and lowers the accuracy of breast cancer detection. For example, a mammogram will pick up cancer in 85% of all women with disease. This number is as high at 98% in women with predominately fatty tissue, but as low as 65% in women with dense tissue. In other words, a third of cancers cannot be seen in dense breast tissue.
Increased breast density is an independent risk factor for developing breast cancer with a 1.9% to 6% increase in risk. These cancers tend to be larger in size, diagnosed at a later stage, have a worse prognosis, and an increased risk of recurrence. Clearly, breast density alone does not determine breast cancer risk. For example, African-American women tend to have a higher percentage of fat in their breasts, but are more likely to have aggressive breast cancer. Asian women tend to have denser breasts, yet have lower risks of developing breast cancer. Thus, ethnicity, family history, age, weight and medical history all play a role in cancer risk.
Why is this information showing up now?
Only recently have we realized that increased breast density is an actual factor in breast cancer risk and this has resulted in advocacy for patient notification. In 2009, Connecticut was the first state to enact a law requiring Radiologists to inform women of breast density. Since then, twenty-seven states have followed their lead and eight more are in the process of doing the same.
So what do I do if I have dense breasts?
Unfortunately, the answer is unclear. Breast MRI or ultrasound may help in the detection of cancer in women with dense breasts, however no studies have demonstrated improved outcomes. In addition, both of these imaging techniques are more likely to show abnormal findings that aren’t cancer which increases the rate of unnecessary biopsies.
While there are no current guidelines for MRI or ultrasound in the presence of dense tissue, there is growing evidence that three-dimensional (3D) mammography increases visualization of breast cancers and reduces the need for recalls. This technology does increase exposure to radiation, but the actual exposure is quite small.
Inherent to this discussion is the value of patient education. Recognizing the limitations of mammography, especially with dense breast tissue, and each patients’ risk profile is paramount to individualized care. Using validated tools and algorithms to calculate breast cancer risk will allow us to make informed screening decisions together and – armed with this information – I believe women can make more thoughtful decisions regarding their own breast cancer screening plan.
written by Joan Loveland, MD
Principal, Bloom OB/Gyn