Three-dimensional mammography (also called digital breast tomosynthesis, digital tomosynthesis, or just tomosynthesis) creates a three-dimensional picture of the breast using X-rays. Several low-dose images from different angles around the breast are used to create the 3-D picture.
A conventional mammogram creates a two-dimensional image of the breast from two X-ray images of each breast.
Three-dimensional mammography is approved by the U.S. Food and Drug Administration, but isn’t yet considered the standard of care for breast cancer screening. Because it’s relatively new, it’s not available at all hospitals and mammogram facilities.
Still, 3-D mammography technology seems to be being adopted faster throughout the United States than digital mammography was -- about 50% of the facilities in the Breast Cancer Surveillance Consortium now offer 3-D mammograms. The Breast Cancer Surveillance Consortium is a collaborative network of seven mammography registries with linkages to tumor and/or pathology registries. The network is part of the National Cancer Institute.
Several studies have found that 3-D mammograms find more cancers than traditional 2-D mammograms and also reduce the number of false positives.
A false positive is when a mammogram shows an abnormal area that looks like a cancer but turns out to be normal. Ultimately, the news is good: no breast cancer. But the suspicious area usually requires follow-up with more than one doctor, extra tests, and extra procedures, including a possible biopsy. There are psychological, physical, and economic costs that come with a false positive.
The rate of false positives has helped fuel the ongoing debate about the value of screening mammograms, especially for women younger than 50. In October 2015, the American Cancer Society recommended that women at average risk of breast cancer start annual screening mammograms at age 45 (instead of 40).
“The issue for women ages 40 to 49 is that with conventional 2-D mammography there are clearly too many false positives,” said Emily Conant, M.D., chief of breast imaging at the University of Pennsylvania Medical Center and member of the Breastcancer.org Professional Advisory Board. “At the same time, we can't even find some of the cancers on 2-D mammography. Many of the false positives in this age group are because the mammogram is their first or ‘baseline’ with no earlier mammograms to compare it to so the radiologist can say, ‘Oh, that is the way her breasts have always been -- this is just normal for her.’”
Dr. Conant was one of the authors of a 2013 study that found that 3-D mammograms led to more cancers being detected in women ages 40 to 49 while simultaneously reducing the number of false positives.
Results from a new study echo the earlier findings: 3-D mammograms offer better cancer detection and fewer false positives in women who are younger than 50.
The research, “Tomosynthesis Impact on Screening Patients 40 to 49,” was presented on Nov. 27, 2016 at the Radiological Society of North America Annual Meeting.
In the study, the researchers looked at the results of 65,457 breast cancer screening exams done in women younger than 50:
- 45,320 had conventional mammograms
- 20,137 had conventional mammograms plus a 3-D mammogram
The exams were done between Jan. 1 and Dec. 31, 2015. The women were not randomly assigned to get conventional or 3-D mammograms. Still, the researchers said their study reflects the way breast cancer screening is done in a real-world clinic setting.
The false positive rate results:
- 115 per 1,000 women who had only a conventional mammogram had false positive results
- 108 per 1,000 women who had a 3-D mammogram had false positive results
This difference was statistically significant, which means that it was likely due to the difference in the type of mammogram and not just because of chance.
The cancer detection rate results:
- conventional mammography found 2.1 cancers for every 1,000 women screened
- 3-D mammography found 3.1 cancers for every 1,000 women screened
- invasive cancer detection rates improved from 1.2 detected with conventional mammography to 1.8 detected with 3-D mammography
According to Stephen Rose, M.D., chief medical officer of Solis Mammography and lead author of the study, this was a 67% relative increase in invasive cancer detection.
These results offer more evidence that 3-D mammograms find more cancers that traditional 2-D mammograms and may help 3-D mammography become part of routine breast cancer screening.
To learn more about 3-D mammography, including how it’s done and how it’s different from 2-D mammography, visit the Breastcancer.org Digital Tomosynthesis page.