The latest results from the ACRIN 6666 study (ACRIN stands for American College of Radiology Imaging Network) show that a breast cancer screening plan that adds ultrasound and MRI to annual mammograms improves breast cancer detection in women with dense breasts.
The results were published in the April 4, 2012 issue of the Journal of the American Medical Association. Read the abstract of Detection of Breast Cancer With Addition of Annual Screening Ultrasound or a Single Screening MRI to Mammography in Women With Elevated Breast Cancer Risk.
Dense breasts have less fatty tissue and more non-fatty tissue compared to breasts that aren't dense. Doctors can tell if breasts are dense by the way they look on a mammogram.
Other research has shown that dense breasts:
- can be twice as likely to develop cancer as nondense breasts
- can be harder for mammograms to detect cancer in; breast cancers (which aren't fatty) are easier to see on a mammogram when they're surrounded by fatty tissue
So an aggressive breast cancer screening plan that includes two or more types of imaging tests makes sense for women with dense breasts.
In this study, 2,309 U.S., Canadian, and Argentinean women with dense breasts and a higher-than-average risk of breast cancer had both a screening mammogram and a breast ultrasound each year. In the study's third year, all the women were offered breast MRI and 703 women had that test. The researchers looked at the benefits of MRI screening using information from 612 women who had MRI.
Ultimately, 111 breast cancers were found in 110 women in the study. Screening mammograms alone, or screening breast ultrasounds alone, each found only a little more than half of the cancers. But together, screening mammograms and ultrasounds found 82% of the cancers. Breast MRI (after three negative mammogram and ultrasound screenings) found another 8% of breast cancers not detected by the other tests. About 10% of the breast cancers weren't found by the imaging tests.
Screening mammograms found 59 breast cancers (53%):
- 33 cancers (30%) were detected by mammography only
- 26 cancers (23%) were detected by mammography, but also by breast ultrasound
Screening mammograms didn't find 51 breast cancers (47%):
- 32 cancers (29%) were detected by breast ultrasound only
- 9 cancers (8%) were detected by MRI (done after mammography and ultrasound)
- 11 cancers (10%) weren't found by any of the imaging tests
One way doctors judge the value and cost-effectiveness of a cancer screening test is to figure out how many screening tests need to be done to find one cancer. The researchers found that to detect one breast cancer:
- 127 screening mammograms would need to done
- 234 additional breast ultrasounds would need to be done
- 68 breast MRIs (after negative mammogram and ultrasound results) would need to be done
In this study, breast ultrasound was very good at finding cancer in dense breasts. About 94% of the areas doctors thought were cancer based on ultrasound results turned out to be cancer. Still, because there were many areas that doctors weren't sure about, only 10% of all the biopsies that were done turned out to be cancer. This means there were many false positives.
A false positive is an area that looks like a cancer, but turns out to be normal. Adding breast MRI to the screening plan of women with dense breasts detected 8% of breast cancers that weren't detected by other imaging tests. Still, adding MRI caused even more biopsies to be done and most of these biopsies turned out to be negative, which means there were more false positives.
For women with dense breasts, a breast cancer screening plan that includes both an annual mammogram and an annual ultrasound is better at finding breast cancer than having only an annual mammogram. Compared to MRI, ultrasound is less expensive. Adding an annual MRI to the plan also increases screening effectiveness, but at a much higher cost than ultrasound.
It's important to know that including a breast ultrasound or breast MRI in screening plans for women with dense breasts will cause more false positives. Besides the concern about a possible breast cancer diagnosis, a false positive usually means more tests (including biopsies) and follow-up doctor visits. The process can be very stressful and upsetting.
Based on the results of this and other studies, it's a good idea to ask your doctor if you have dense breasts, as well as about your risk of breast cancer. If your breasts are dense or your risk of breast cancer is higher than average, an aggressive screening plan that includes breast ultrasounds and/or breast MRIs along with mammograms may make sense for you. Ask your doctor to explain the risks and benefits of having ultrasound or MRI in your screening plan. Together you can develop a screening plan that's right for you.
Visit the Breastcancer.org Breast Cancer Tests: Screening, Diagnosis, and Monitoring pages to learn more about screening tests.
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