Using 3D mammography may reduce the number of women who have a biopsy for a suspicious lesion after an abnormal mammogram, according to a study.
The research was published online on March 19, 2019, in the journal Radiology. Read “The Potential Impact of Digital Breast Tomosynthesis on the Benign Biopsy Rate in Women Recalled within the UK Breast Screening Programme.”
What is 3D mammography?
Three-dimensional (3D) mammography (also called digital breast tomosynthesis, digital tomosynthesis, or just tomosynthesis) creates a 3D picture of the breast using X-rays. Several low-dose images from different angles around the breast are used to create the 3D picture.
A conventional mammogram creates a two-dimensional image of the breast from two X-ray images of each breast.
3D mammography is approved by the U.S. Food and Drug Administration (FDA), but isn’t yet considered the standard of care for breast cancer screening. Because it’s a newer technology, it may not be available at all hospitals and mammogram facilities.
A number of studies have found that 3D mammograms find more cancers than traditional 2D 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 mammogram debate
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).
Doctors who question the value of mammograms say that while mammograms do save lives, for each breast cancer death prevented, three to four women are overdiagnosed. Overdiagnosis means either:
- a screening mammogram finds a suspicious area that would have been eventually diagnosed as cancer by other means, without any effect on prognosis
- a screening mammogram finds a suspicious area that never would have affected a woman’s health if it hadn’t been found or treated
Studies on the benefits and possible harms of screening mammograms and the resulting stories in the media have fueled an ongoing debate about the value of mammograms.
Many radiologists believe that 3D mammograms are a better mammogram for breast cancer screening and that 3D mammograms may help ease concerns about the value of mammograms. This is why many studies are comparing 3D mammograms to traditional 2D mammograms.
How this study was done
Done in the United Kingdom, the study included 827 women who had either a 2D mammogram or a breast MRI for breast cancer screening between Nov. 13, 2015, and July 29, 2016, and were called back because of a suspicious area on the screening imaging. The women’s average age was about 57.
When the women returned for their recall appointment, they had:
- a breast exam
- another 2D mammogram
- an ultrasound of the suspicious area
- a biopsy, if needed
In addition, all the women had a 3D mammogram as part of this study. The 3D mammogram results were not used to make biopsy decisions.
The 3D mammograms were read by two radiologists within 6 weeks of the recall appointment. These radiologists did not know the results of the women’s recall appointments, meaning they didn’t know if the women had a biopsy or not. If the two radiologists disagreed about the results of the 3D mammogram, a third radiologist read the 3D mammogram and the three doctors reached a consensus opinion.
The radiologists answered two questions when reading each 3D mammogram:
- Did the 3D mammogram identify a suspicious area?
- If there was a suspicious area on the 3D mammogram, did it require a biopsy?
The researchers compared the results of the 3D mammograms to the results of the 2D mammograms for each of the 827 women who had a recall appointment.
- 582 women were classified as having normal 3D mammograms by both radiologist readers
- 245 of the 827 women were classified as needing a recall appointment based on 3D mammogram results
- 16 women needed the third radiologist’s opinion to read the 3D mammogram results
- 2 cancers were missed by 3D mammogram, but found by 2D mammogram
- 2 cancers that were missed by 2D mammogram were found by 3D mammogram
Overall, 571 of the 827 women had a biopsy at their recall appointment, which found 142 cancers. The results of the 3D mammograms indicated that only 298 women would have needed a biopsy, which would have found 142 cancers.
Researchers use a statistic called “positive predictive value” to evaluate the effectiveness of a screening test. Positive predictive value is the likelihood that a person with a positive test result truly has the disease. The higher the positive predictive value, the more likely the screening test is to accurately identify a person with the disease.
In this study, the positive predictive value of 2D mammography was 24.9%. The positive predictive value of 3D mammography was 47.6%, nearly double.
"The thin slice images of the breast taken with [3D mammography] reduce the effect of tissue overlap, which often leads to cancers being missed or to women who don't have breast cancer being recalled for diagnostic imaging," said lead researcher Nisha Sharma, MBChB, director of breast screening and clinical lead for breast imaging at Leeds Teaching Hospital NHS Trust, Seacroft Hospital. "[3D mammography allows for improved reader accuracy and confidence in determining if a mammographic abnormality is concerning or not, leading to a reduction in the number of biopsies performed. Our study validates that [3D mammography] can help in the diagnostic workup of mammographic abnormalities and reduce harm to women through fewer false positive biopsies without any reduction in the cancer detection rate."
What this means for you
Three-dimensional mammography technology seems to be being adopted faster throughout the United States than conventional 2D digital mammography was. According to 2018 statistics from the FDA, about 4,000 facilities out of 8,726 certified mammography facilities in the county offer 3D mammograms.
If you would like to have a 3D mammogram and aren’t sure your facility offers them, call and check before you make your appointment. If the facility doesn’t offer 3D mammograms, ask your doctor to recommend a facility that does.
The results of this study echo other results suggesting that 3D mammograms are more accurate than 2D mammograms and may help 3D mammography become part of routine breast cancer screening.
To learn more about 3D mammography, including how it’s done and how it’s different from 2D mammography, visit the Breastcancer.org Digital Tomosynthesis page.
Written by: Jamie DePolo, senior editor