Several large studies, including a review by the U.S. Preventive Services Task Force in 2009 and a study on the causes of death in the United Kingdom in 2013, have questioned the value of screening mammograms.
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
False positive results from screening mammograms also have helped fuel the debate about the value of breast cancer screening. When a mammogram shows an abnormal area that looks like a cancer but turns out to be normal, it’s called a false positive. 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.
These studies and the resulting stories in the media have fueled an ongoing debate about the value of screening mammograms.
While mammograms aren’t perfect, they are one of the best tools we have to find breast cancer early. So researchers are always looking for ways to improve the accuracy of mammogram results.
While other screening techniques, such as breast MRI and breast ultrasound, have improved breast cancer detection, they haven’t reduced the rate of false positives.
A study suggests that combining digital mammography with three-dimensional (3-D) mammograms detects more breast cancers with fewer false positive results compared to digital mammography alone.
The research was published in the June 25, 2014 issue of The Journal of the American Medical Association. Read “Breast Cancer Screening Using Tomosynthesis in Combination With Digital Mammography.”
Three-dimensional mammography is also called tomosynthesis or digital tomosynthesis. Tomosynthesis creates a 3-D 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.
Digital mammograms record the images of the breast into a computer instead of on to film.
In this study, the researchers looked at the results of 454,850 breast imaging tests done between March 2010 and December 2012:
- 281,187 digital mammograms
- 173,663 digital mammograms plus a 3-D mammogram
Breastcancer.org Professional Advisory Board member Emily Conant, M.D., chief of breast imaging at the Perelman School of Medicine at the University of Pennsylvania, was one of the authors of the study.
Looking at only the digital mammogram screenings, the researchers found that 29,726 women were called back for more testing, which led to:
- 5,056 biopsies
- 1,207 breast cancer diagnoses (815 invasive cancers and 392 DCIS)
Looking at screening with a combination of digital mammography and 3-D mammography, the researchers found that 15,541 women were called back for more testing, which led to:
- 3,285 biopsies
- 950 breast cancer diagnoses (707 invasive cancers and 243 DCIS)
This means that per 1,000 screening tests:
- 107 women were recalled for more testing with digital mammography alone and 91 women were recalled with digital mammography plus 3-D mammography
- 4.2 cancers were found with digital mammography and 5.4 cancers were found with digital mammography plus 3-D mammography
These differences were significant, which means that they’re due to the difference in screening techniques and not just because of chance.
In other words, compared to digital mammography alone, screening that included both digital mammography and 3-D mammography:
- found 41% more invasive cancers
- reduced false positives by 15%
Three-dimensional mammography is approved by the U.S. Food and Drug Administration, but isn’t yet the standard of care for breast cancer screening. While more hospitals are installing 3-D mammogram equipment, it’s not available everywhere. The researchers who did the study hope that their work will draw attention to the technology and increase access to it.
While the results of this study are extremely promising, it’s important to keep several things in mind:
- This was a retrospective study. The researchers looked back at breast cancer screening records and the women were not randomly assigned to have either a digital mammogram alone or a digital mammogram plus a 3-D mammogram. More research, including a randomized study, is needed before 3-D mammography becomes part of routine breast cancer screening.
- A 3-D mammogram costs more than a digital mammogram and not all insurance companies cover 3-D mammograms. Some mammography centers charge women an extra $50 for a 3-D mammogram if it’s not covered by insurance.
- Because it’s another imaging test, 3-D mammography exposes women to additional radiation. Researchers are looking at ways to replace a standard mammogram image with one created from 3-D mammography images while reducing radiation exposure.
Visit the Breastcancer.org Digital Tomosynthesis page to learn more about how 3-D mammography is done and how it’s different from a two-dimensional mammogram.