MedicalResearch: What is the background for this study?
Dr. Sprague: Mammographic breast density refers to the appearance of breast tissue on a mammogram. High breast density means that there is a greater amount of glandular tissue and connective tissue, which appears white on a mammogram. It is more difficult to detect breast cancer on a mammogram when there is greater breast density. It has also been shown that women with dense breasts are at a higher risk of developing breast cancer. Because of these two factors, women with dense breasts have a greater chance of developing breast cancer after a normal screening mammogram than women whose breasts are not dense. Many states have now passed laws that require mammography facilities to inform women with dense breasts so that they are aware of this. Similar legislation is now under consideration at the national level. More than 40% of women undergoing mammography screening have dense breasts.
Researchers are trying to determine whether supplemental breast cancer screening with other tools would improve outcomes for women with dense breasts. One possible approach is to use ultrasound imaging to screen for breast cancer in women with dense breasts after they have had a normal mammogram. We wanted to estimate the benefits, harms, and cost-effectiveness of this approach compared to mammography screening only. No randomized trials or observational studies have assessed long term outcomes after ultrasound screening for women with dense breasts, but we have short term data on how often cancer is diagnosed by ultrasound screening and how often false positive exams occur. We used computer simulation modeling to estimate long term outcomes by combining the currently available data on mammography and ultrasound screening with the best available data on breast cancer risk and survival.
MedicalResearch: What are the main findings?
Dr. Sprague: We estimated that for every 10,000 women with dense breasts receiving ultrasound screening exams after a normal mammogram between the ages of 50-74, about 4 breast cancer deaths would be prevented but an extra 3500 biopsies would occur in women who didn’t have breast cancer. It would cost about $325,000 for every year of healthy life gained. Using ultrasound screening for the 10% of the population with the highest breast density (rather than all 40% with dense breasts) offered a more favorable balance of benefits and harms but would still result in 1900 biopsies for every 3 breast cancer deaths prevented, and cost about $250,000 per year of life gained. Beginning ultrasound screening at age 40 instead of age 50 produced only a slight increase in breast cancer deaths prevented but substantially increased the number of biopsies and costs.
MedicalResearch: What should clinicians and patients take away from your report?
Dr. Sprague: The take-home message is that performing ultrasound screening for all women with dense breasts after a normal mammogram would produce relatively small benefits while substantially increasing the number of biopsies for women without cancer. And it would not be considered cost-effective. We need to identify better strategies to improve breast cancer screening outcomes for women with dense breasts.
MedicalResearch: What recommendations do you have for future research as a result of this study?
Dr. Sprague: The next steps are to develop and evaluate other strategies for improving breast cancer screening for women with dense breasts. For example, it may be possible to more accurately identify women who would benefit from supplemental ultrasound screening – perhaps women who have other breast cancer risk factors in addition to having dense breasts. The continuing improvement of mammography may also result in better screening outcomes for women with dense breasts. We are studying the performance of digital breast tomosynthesis (also known as 3D mammography) which may improve the detection of cancer among women with dense breasts without increasing the false-positive rate.
Sprague BL, Stout NK, Schechter C, van Ravesteyn NT, Cevik M, Alagoz O, et al. Benefits, Harms, and Cost-Effectiveness of Supplemental Ultrasonography Screening for Women With Dense Breasts. Ann Intern Med. [Epub ahead of print 9 December 2014] doi:10.7326/M14-0692