This article is authored by the Mayo Clinic Center for Individualized Medicine. The mission of the Center is to discover and integrate the latest in genomic, molecular and clinical sciences into personalized care for patients.
A picture is worth a thousand words. While that saying may be true, for the more than 50 percent of all women who have dense breast tissue, a picture from traditional, 2-D mammography may not tell the full story about whether they have breast cancer.
“Breast density is like the wolf in sheep’s clothing. Both tumors and dense breast tissue appear white on a mammogram. A traditional 2-D mammogram may not distinguish between the two. That’s why mammograms find as few as 40 percent of cancers in women with dense breasts,” says Deborah Rhodes, M.D., a Mayo Clinic Breast Clinic physician.
“If tumors are obscured by dense tissue on a mammogram, the tumor may go undetected for a year or longer during which time the tumor will grow – which is a significant problem when you consider how closely survival from breast cancer is linked to tumor size at diagnosis. If we discover a tumor when it is less than 1 centimeter, that patient has over a 90 percent chance of surviving. If we could reliably find tumors in dense tissue when they are small, more lives could be saved," adds Dr. Rhodes.
In addition to dense breast tissue masking tumors on a mammogram, research has shown that women with dense breast tissue have a higher risk of developing breast cancer. Many states have now passed legislation mandating that women found to have dense breasts on a mammogram be provided with information about the impact of breast density on breast cancer detection and risk.
Because both Minnesota and Arizona have this legislation, and because national guidelines on breast cancer screening differ, Mayo Clinic breast specialists developed consensus guidelines for breast cancer screening in women with dense breasts.
Bringing dense breast tissue into focus - 3-D mammograms and molecular breast imaging (MBI)
In order to provide the best screening to detect breast cancer, Mayo Clinic physicians recommend that women with dense breasts initially have a 3-D mammogram and be given the option to have further screening with molecular breast imaging (MBI).
- How it works: Like a 2-D mammogram, a 3-D mammogram (also known as digital mammography with tomosynthesis) is an X-ray. It is also an anatomic test, which means cancer is detected based on changes in how the breast anatomy looks. Rather than an image that is formed from pictures taken from top to bottom and side to side like a 2-D mammogram, a 3-D mammogram takes multiple pictures of the breast. With the 3-D mammogram, the breast tissue can be analyzed layer by layer.
- The patient experience: Getting a 3-D mammogram feels the same as a standard mammogram. Your breast is compressed and X-rays pass through the breast to make pictures of your breast tissue.
- Advantages: Research shows that 3-D mammograms can detect slightly more cancers than standard 2-D mammograms. The main benefit of the test is that it reduces the chance that you will be recalled for additional testing because of findings that are not due to cancer.
- How it works: MBI, a technology developed at Mayo Clinic, is different than a 3-D mammogram because it is a functional test, not an anatomic test. That means the pictures it creates show differences in tissue activity. Tissues with more active cells, like cancers, light up or appear brighter than less active normal tissue using this test.
- The patient experience: Before the test starts, you receive an injection of a small dose of a radioactive tracer into a vein in your arm. The tracer accumulates in fast-growing cells, like cancer cells. Then a special camera is used to image the breast. The effective dose of radiation used for this test is higher than that used for a traditional 2-D mammogram, but still considered a safe dose.
- Advantages: This test more clearly distinguishes between dense breast tissue and tumors. A Mayo Clinic study led by a team of breast clinicians, physicists and radiologists showed that molecular breast imaging, when compared to traditional 2-D mammography, detects more than three times the number of cancers in women with dense breasts.
Dense breast tissue – what you should know
Women with dense breast tissue have a higher proportion of dense tissue compared to fatty tissue in their breasts. You can find out whether you have dense breast tissue by talking with your physician and reading your mammogram report.
Factors that lead to women having dense breasts include:
- Genetics: Many women with dense breasts inherit this characteristic. This is the most common reason for women who have a higher breast density.
- Age: Younger women are more likely to have dense breasts. Breast density declines with age, but not at a predicable rate. Two-thirds of women in their 40s have dense breasts and one third of women who are post-menopausal have dense breasts.
- Weight: Women who are thinner and have a lower body mass index (BMI) are more likely to have dense breasts, compared to women who are overweight or obese.
- Hormonal levels: Women who have had children have lower breast density than women who have not. In addition, women taking hormone therapy are more likely to have dense breasts.
Adjusting the lens – researchers work to refine screening tools
Mayo Clinic Center for Individualized Medicine has supported development of molecular breast imaging as an individualized approach to cancer screening and will continue to support research that refines this technology in order to provide patients with dense breast tissue the best care.
“Our goal is to identify the best tool to screen for and diagnose cancer at its earliest stages, when it is more treatable. By finding the best individualized care for women with dense breasts, I think we can greatly reduce the number of breast cancers diagnosed when they are already advanced - cancers that were not visible on an x-ray. We have already demonstrated that MBI can detect many cancers – including advanced cancers – that were not seen on traditional 2-D mammography. Our future research will continue to evaluate the effectiveness of 3-D mammograms and MBI. While this research is ongoing and important, MBI is available now as a tool for women who seek additional screening because they have dense breasts,” says Dr. Rhodes.