One of the biggest hopes for 3D mammograms, the new generation of breast cancer screening, was that they would reduce the number of times a result looked abnormal even though there was no cancer.
Such false-positive mammograms can cause tremendous anxiety, and require more tests or even a biopsy. Women have described feeling “panicked” when getting a callback.
But there was only a modest difference between the newer and older technology when researchers calculated the probability of at least one false-positive result after 10 years of annual screening, a new investigation has found.
About 50% of women were expected to experience a false-positive with 3D mammograms over that period, compared to 56% with 2D mammograms, researchers reported in JAMA Network Open.
The risk was lower for women who were screened every other year or those who were older.
For women with extremely dense breasts, the false-positive rates were similar with both types of mammograms.
The results were surprising, said Diana Miglioretti, senior author of the study and division chief of biostatistics at the UC Davis Department of Public Health Sciences in Davis, California.
“It’s disappointing. I was really hoping that it would greatly reduce the percentage of women experiencing false positives because it is so stressful for women,” Miglioretti, who is also a researcher at the UC Davis Comprehensive Cancer Center, told TODAY.
“We don’t have a perfect test yet, unfortunately.”
'Try not to be stressed'
The findings are based on data from about 1 million women and almost 3 million mammograms performed between 2005 and 2018 at 126 breast imaging facilities in the U.S.
Standard digital mammograms, the older 2D technology, consist of X-rays of the breast from only two different angles — top to bottom and side to side.
But digital breast tomosynthesis, the formal name for 3D mammograms, involves taking many low-dose X-rays of the breast as the machine moves in a small arc, creating image slices that allow doctors to see the breast tissue more clearly in three dimensions, according to the American Cancer Society.
There is some evidence this newer technology, which is now widely used in the U.S., may improve cancer detection, Miglioretti said.
Previous research has found false-positive results are common. About 12% of patients who undergo digital screening mammograms get callbacks, the study noted. Of those recalls, only 4.4%, or 0.53% of all screening mammograms, result in a cancer diagnosis.
It’s important to remember mammograms are a screening test, not a diagnostic one, she added.
“It’s really just to identify women who need to go on for diagnostic mammography that’s more focused imaging… to see if it’s cancer or not,” she said.
“We need to reassure women that just because of the call for additional work up, it’s typically not cancer, it’s typically totally benign. We just need to get a closer look at that lesion.”
Still, callbacks can involve time, expense and invasive tests. It can sometimes take weeks to get a follow-up appointment for additional imaging — a highly-stressful time for a woman waiting to get the results. Some women may be asked to get a biopsy, requiring even more time to schedule that procedure and wait for the findings.
Screening every other year
Annual mammograms are the “dominant practice” in the U.S., but women could cut their risk of false-positives by being screened every other year — simply because they’re getting fewer tests, the study noted.
The U.S. Preventive Services Task Force recommends screening every two years for women 50 to 74 years old.
The American Cancer Society has slightly different recommendations: It advises women 45 to 54 years old to get a mammogram every year, then switch to every other year if they prefer.
“I strongly believe that most women do just fine with screening every other year,” Miglioretti said.
“Cancer is detected still at an early stage, and it greatly reduces the harms of screening,” she added, including the risk of false-positives and over-diagnosis — or aggressive treatment for a slow-growing breast cancer that would have never harmed a woman in her lifetime.
Annual mammograms may still be better for women with strong risk factors, younger women in their 40s, post-menopausal women receiving hormone therapy and women with obesity, Miglioretti said.
Women with dense breasts will experience more false-positives and may need supplemental screenings such as a breast MRI or ultrasound because both cancer and dense tissue show up as white on a mammogram.
If you get a callback after the test, be aware it’s normal.
“Most women are going to experience this, try not to be stressed,” Miglioretti said. “The chance of cancer is very rare… chances are it’s going to turn out to be a benign finding.”