Breast density can be a useful indicator of breast cancer risk because the higher the breast density, the higher the risk of breast cancer. Adding four additional risk factors to the matrix can increase the predictive value significantly.
“As a primary care provider, I find that it needs to be easy,” said Karla Kerlikowske, MD, Professor of Medicine, Epidemiology and Biostatistics, University of California, San Francisco. “Breast density is an important risk factor for breast cancer. It is prevalent and it is highly predictive. The Breast Cancer Surveillance Consortium risk calculator adds additional risk factors to give you an even easier, more effective tool to evaluate an individual patient’s risk for breast cancer.”
Dr. Kerlikowske discussed the background and details of breast density Sunday morning during the John I. Brewer Memorial Lecture “Mammographic Breast Density: What You Need to Know.” The free BCSC risk calculator has been available online for some time and is now available as a free iPhone app. An Android version remains in development.
Breast density is a mammographic feature based on the physiologic composition of the breast. More whiteness in the mammogram means the tissue being imaged is denser. A darker image means more fat.
Breast density is graded from a to d using the BI-RADS reporting system, from almost entirely fatty (a) fat to scattered fibroglandular density (b), heterogeneously dense (c), and extremely dense (d). Some practitioners may be more familiar with the numerical scale that used one through four for the same classifications.
Regardless of the scale used, women with denser breast tissue are at higher risk for all types of breast cancer. Women whose breasts are 50 percent dense tissue have a risk ratio of 3.4 for developing breast cancer. The risk ratio rises to 5.3 for women whose breasts are 75 percent dense tissue.
Between 30 and 60 percent of breast density is derived from genetic factors, Dr. Kerlikowske said. Women tend to lose breast density after menopause, although hormone replacement therapy prevents this age-related loss of breast density. Increasing body mass index also reduces breast density. Tamoxifen reduces breast density in some women, one mechanism by which the agent reduces the risk for breast cancer.
“There are not many modifiable risk factors for breast density and breast cancer, unlike smoking for lung cancer,” she said. “But if you can modify breast density, you can modify the risk for breast cancer.”
But breast cancer risk is based on more than breast density. It is entirely possible for a woman with a normal mammogram to develop aggressive breast cancer. BCSC has developed a five-year risk calculator for breast cancer based on five risk factors: age, race/ethnicity, family history of breast cancer in a first-degree relative, history of breast biopsy, and BI-RADS breast density.
The model is based on the BCSC database of about ten million mammograms from 2.5 million women and 125,000 breast cancers. Depending on the number of additional risk factors, even women with almost entirely fatty breasts could be at increased risk for breast cancer.
“Risk factors can help you identify women who need more frequent screening because they are at higher risk,” Dr. Kerlikowske said. “We may be able to improve the harm/benefit ratio of screening by incorporating risk factors into our standard models.”