Christina Silcox, PhD, and Danielle Shapiro, MD, MPH, Cancer Prevention and Treatment Fund
When breast cancer is detected early—before it has spread—it is easier to treat and women have a much better chance of living a long life. Screening refers to tests that are given to people who have no symptoms, to find out if they might have a disease. Mammograms are the best way to screen women for breast cancer.
Forty million mammograms are performed each year,2 but the technology is evolving. Depending on where a woman lives, she may be able to choose from among three different types of mammography. Does it matter what kind of mammogram she gets?
A New Type of Digital Test: 3D Mammography
3D mammograms, also known as tomosynthesis or “tomo,” use the same x-ray technology as regular “2D” mammograms. The procedure is the same from the patient’s point-of-view, although it will take a few seconds longer. In both 3D and 2D mammograms, the breast is compressed between two plates. In 2D mammograms, which take images only from the front and side, this may create images with overlapping breast tissue. Because 3D mammography provides images of the breast in “slices” from many different angles, finding abnormalities and determining which abnormalities seem potentially worrisome may be easier with 3D tests. On the other hand, 3D mammography is more expensive than 2D, and your insurance may charge you more if you use 3D.
Since 2013, the FDA has concluded that a low-dose 3D digital mammography is at least as accurate as 2D mammography. 2D digital images can also be obtained from the 3D mammography data.
Differences between 2D and 3D Mammograms
Because it was initially not known how accurate 3D mammograms would be, most research compared 2D mammograms to a combination of 3D mammograms and 2D mammograms. That was the information that Hologic, the company that developed the first 3D mammography machines, needed to provide to the FDA when they applied for FDA approval. The studies were funded by Hologic and evaluated the mammograms from their machines. We do not know if the results would be similar to other companies’ mammography machines.
The results of the studies showed that the combination of 3D and 2D was more accurate than 2D digital or film mammograms, although the difference in accuracy was tiny for each patient.6,7,8,9,10,11 In addition, women who undergo screening with 3D+2D mammography are less likely to be called back for more testing due to a suspicious finding that turns out not to be cancer. This means fewer false alarms caused by inaccurate findings.7,8,12 But, using two tests is not practical and can be harmful because it exposes women to more radiation. The important question is: Do the 3D tests hold up on their own?
An article published in 2017 in the prestigious medical journal JAMA examined the benefits of 3D mammograms. The study compared the number of call backs and the numbers of cancers diagnosed before the next scheduled screening in women who had 3D mammograms vs. standard 2D mammograms. For the more than 23,000 women undergoing an initial 2D mammogram followed by 3 years of annual 3D mammograms, the use of 3D tests slightly reduced the number of women who got called back (10% in the 2D group vs. 9% in the 3D group) and the number of cancers detected in the months between the annual mammograms. Following 2D mammography, about 7 out of 10,000 women were diagnosed with cancer before their next annual mammography, compared to 5 out of 10,000 of the women who underwent 3D mammography screening. Although the differences are very small, they are statistically significant, which means they did not happen by chance.
Even though the differences are small, 3D tests seem to have a small advantage over 2D tests because they are slightly better at finding dangerous cancers, reducing the number of repeat tests, and reducing the amount of time a woman has to wait to find out.
While the benefits of 3D mammograms appear to be tiny for an individual woman, the benefits of the 3D test could add up for a large population of women. For example, a study examining over 44,000 screening tests, including over 28,000 3D mammograms, over 5 years found that 3D screening detected significantly smaller invasive breast cancers (about 1.5 cm (about ½ inch) vs. 2.3 cm (about 1 inch). And, the cancers that were detected by 3D tests were less likely to have spread to the lymph nodes (about 15% vs. 31%). Finding a cancer that is smaller and hasn’t spread to the lymph nodes means that a woman would require less aggressive treatment of her cancer, such as less radical surgery and fewer chances of needing chemotherapy.
Even if 3D mammography is more accurate, does it save lives?
Experts used to believe that mammograms reduced breast cancer deaths by about 14% to 32%, based on very old studies. Newer studies conclude that screening mammography has a smaller impact, decreasing breast cancer deaths by about 2%. It is important to keep in mind that these studies include data up to the year 2005 when it was common practice to recommend mammograms every year. Experts now recommend screening be done every 2 years for women of average risk and believe it will not increase the percentage of women dying from breast cancer, but we don’t yet know exactly what impact this new screening practice will have.
Why would mammography save fewer lives today than in previous years? It may be because cancer treatments have gotten better, even for more advanced cancers. Also, as mammography has improved, it is detecting abnormalities and cancers that may not be fatal. Even if 3D mammograms can detect invasive cancers when they are smaller and less dangerous, more research is needed to determine if 3D mammography saves more lives.
Harms of 3D screening:
The 3D test takes a few seconds longer than 2D digital or film mammography (adding a few seconds of discomfort). The newer, low-dose 3D mammography uses less radiation than a 2D mammography.
Because digital mammography—2D and 3D—is relatively new, no one has figured out exactly what all the health risks and benefits are.
2D screening mammograms are free for patients covered by healthcare insurance under the Affordable Care Act. Some insurers will not cover 3D mammograms, and others charge women a surcharge. However, Medicare began covering 3D mammography in 2015 and some states are beginning to mandate coverage.13
The Bottom Line
On average, 3D mammography is slightly better at detecting cancer, but it is not clear how much that benefits the average woman.
It is important to remember that experts now agree that most women under 50 or over 75 do not need to undergo screening mammography and that the average woman only needs to undergo screening mammography every two years instead of annually. See our article When should women start regular mammograms? 40? 50? And how often is “regular”? for more information.
- National Cancer Institute. “SEER Stat Fact Sheets: Breast Cancer.” http://seer.cancer.gov/statfacts/html/breast.html (Accessed October 12, 2015). ▲
- S. Food and Drug Administration. “Radiation-Emitting Products.” http://www.fda.gov/Radiation-EmittingProducts/MammographyQualityStandardsActandProgram/FacilityScorecard/ucm113858.htm (Accessed October 12, 2015). ▲
- Pisano ED, Gatsonis C, Hendrick E, et al. Diagnostic Performance of Digital versus Film Mammography for Breast-Cancer Screening. New England Journal of Medicine, 2005; 353(17): 1773-1783. ▲
- Rosselli del Turco M, Mantellini P, Ciatto S, Bonardi R, Martinelli F, Lazzari B, Houssami N. Full-field digital versus screen-film mammography: Comparative accuracy in concurrent screening cohorts. American Journal of Roentgenology 2007; 189(4): 860-866. doi: 10.2214/AJR.07.2303. ▲
- Kerlikowske K, Hubbard RA, Miglioretti DL, Geller BM, Yankaskas BC, Lehman CD, Taplin SH, & Sickles EA. Comparative effectiveness of digital versus film-screen mammography in community practice in the United States. Annals of Internal Medicine 2011; 155: 493-502. ▲
- Sharpe RE Jr, Venkataraman S, Phillips J, Dialani V, Fein-Zachary VJ, Prakash S, Slanetz PJ, Mehta TS. Increased Cancer Detection Rate and Variations in the Recall Rate Resulting from Implementation of 3D Digital Breast Tomosynthesis into a Population-based Screening Program. Radiology. 2015 Oct 9:142036 ▲
- Greenberg JS, Javitt MC, Katzen J, Michael S, Holland AE. Clinical performance metrics of 3D digital breast tomosynthesis compared with 2D digital mammography for breast cancer screening in community practice. AJR Am J Roentgenol 2014;203(3):687–693. ▲
- Friedewald SM, Rafferty EA, Rose SL, et al. Breast cancer screening using tomosynthesis in combination with digital mammography. JAMA 2014;311(24):2499–2507. ▲
- Lei J, Yang P, Zhang L, Wang Y, Yang K. Diagnostic accuracy of digital breast tomosynthesis versus digital mammography for benign and malignant lesions in breasts: a meta-analysis. Eur Radiol 2014;24(3):595–602. ▲
- S. Food and Drug Administration. “Summary of Safety and Effectiveness Data (SSED): Selenia Dimensions 3D System.” http://www.accessdata.fda.gov/cdrh_docs/pdf8/P080003S001b.pdf (Accessed November 20, 2013). ▲
- Rose S, Tidwell AL, Bujnoch LJ, Kushwaha AC, Nordmann AS, & Sexton R. Implementation of breast tomosynthesis in a routine screening practice: An observational study. AJR online; March 22, 2013. doi: 10.2214/AJR.12.9672. ▲
- Skaane P, Bandos AI, Gullien R, Eben EB, Ekseth U, Haakenaasen U, Izadi M, Jebsen IN, Jahr G, Krager M, Niklason LT, Hofvind S, & Gur D. Comparison of digital mammography alone and digital mammography plus tomosynthesis in a population-based screening program. Radiology 2013; 267(1): 47-56. doi: 10.1148/radiol.12121373. ▲
- McDonald ES, Oustimov A, Weinstein SP, Synnestvedt MB, Schnall M, Conant EF. Effectiveness of Digital Breast Tomosynthesis Compared With Digital MammographyOutcomes Analysis From 3 Years of Breast Cancer Screening. JAMA Oncol. 2016;2(6):737–743. doi:10.1001/jamaoncol.2015.5536
- mandates 3-D mammogram coverage. Philadelphia Inquirer. Marie McCullough October 6, 2015 http://www.philly.com/philly/health/20151006_Pa__mandates_3-D_mammogram_coverage.html ▲
- Esserman LJ, Thompson IM, & Reid B. Overdiagnosis and overtreatment in cancer: An opportunity for improvement. Journal of the American Medical Association 2013: online version, E1-E2. doi:10.1001/jama.2013.108415. ▲
- McDonald, E., Oustimov, A., Weinstein, S., et al. (2016). Effectiveness of Digital Breast Tomosynthesis Compared With Digital Mammography. Journal of the American Medical Association. Accessed from https://jamanetwork.com/journals/jamaoncology/fullarticle/2491465 on June 5, 2018.
- Neal, C. and Philpotts, L. (2017). Breast Imaging (Multimodality Screening and Breast Density). Accessed from http://archive.rsna.org/2017/17039959.pdf
- Kalager M, Zelen M, Langmark F, Adami H-O. Effect of screening mammography on breast-cancer mortality in Norway. N Engl J Med. 2010;363(13):1203–1210.
- Kaunitz, A. (2010). Just How Much Does Screening Mammography Reduce Mortality From Breast Cancer. OBG Manag. Accessed from https://www.mdedge.com/obgmanagement/article/64117/gynecologic-cancer/just-how-much-does-screening-mammography-reduce.
- Philpotts, L. (2017). Screening for Breast Cancer Breast Imaging. Accessed from http://ctcancerpartnership.org/wp-content/uploads/2017/09/Beast-Cancer-Liane-Philpotts.pdf.