Three-dimensional breast scans detected more cancers with fewer false findings than standard digital mammograms in the largest study to date of the newer screening technology.
The improvements seen over mammography -- which has been criticized for missing deadly cancers and leading many women to undergo needless biopsies -- means that the 3-D screening, called tomosynthesis, is likely to become more routine over the next few years. Fewer than 1 in 6 women who have annual breast screening currently get the 3-D scan.
The research, conducted at Massachusetts General Hospital and 12 other institutions, reviewed nearly half a million breast screening scans conducted in 2010 through 2012. The study found that nearly 3 in 1,000 women who were screened just with a standard digital mammogram had cancers detected that were invasive and potentially life-threatening compared with slightly more than 4 in 1,000 women who had digital mammography along with tomosynthesis, after the imaging technology came on the market in 2011.
Findings were published Tuesday in the Journal of the American Medical Association, and the research was funded by the National Cancer Institute and Hologic, the Bedford-based company that is the sole manufacturer of the 3-D imaging machine in the United States.
“Virtually all of the additional cancers that we found were invasive cancers, the ones we worry about,” said study co-author Dr. Elizabeth Rafferty, a breast imaging specialist at Mass. General, “rather than DCIS.” Ductal carcinoma in situ are tiny malignancies that haven’t spread into the surrounding tissue and are normally cureable.
Breast tomosynthesis is performed just like a mammogram -- with the breast flattened between two plates like a pancake -- except the X-ray camera rotates to snap 15 images from all angles. Software combines the images to create a 3-D rendering of the breast that radiologists can examine layer by layer, instead of examining the bird’s eye view from the traditional two-dimensional X-ray.
Two smaller studies in Europe, each conducted at a single imaging facility, previously suggested that tomosynthesis improved cancer detection rates, but this new one is much larger, conducted at multiple institutions, and the first in the United States to demonstrate that 3-D mammograms have the potential to detect cancer at an earlier stage when it’s more curable.
Screening experts, however, caution that lifesaving benefits were not seen in the new study. “Finding more cancers isn’t our goal,” said Dr. Lisa Schwartz, professor of medicine at the Dartmouth Institute for Health Policy and Clinical Practice. “It’s about reducing breast cancer deaths. We don’t know whether this new technology finds more cancers destined to kill people.”
Women who had tomosynthesis along with digital mammograms were also less likely to be told to come back for additional imaging tests for suspicious findings: 9 percent of them were recalled compared to nearly 11 percent of those who only had digital mammograms, but the biopsy rate was slightly higher for women undergoing 3-D imaging -- 1.9 percent compared to 1.8 percent in the control group.
The 3-D imaging also exposes women to twice as much radiation as they would typically have with a digital mammogram because it’s used in conjunction with the screening X-ray. A newer version enables radiologists to combine both into one imaging test, reducing radiation exposure by half, Rafferty said, but it’s not yet widespread and likely won’t become available at Mass. General until early next year.
Public health groups have conflicting recommendations on breast screening: The American Cancer Society, for example, recommends that women get annual mammograms every year beginning at age 40, while the government-sponsored US Preventive Services Task Force recommends that women get screened every two years from ages 50 to 74.
Those recommendations are based on research examining the benefits and drawbacks of traditional mammograms, not tomosynthesis. Whether the new research finding tips the balance more in favor of breast screening, screening experts say, remains to be seen.
“There’s a debate about the harms of screening and overdiagnosis of breast cancers from mammograms and to me, this doesn’t resolve that,” said Dr. Etta Pisano, a breast imaging radiologist at the Medical University of South Carolina who wrote an editorial that accompanied the study.
Some women may benefit more from tomosynthesis than others, such as those with dense breasts that tend to obscure tumors -- which are also dense -- in traditional 2-D mammograms. “Maybe women who don’t have dense breasts do just as well with digital mammograms,” Pisano added. “I don’t think every woman should be seeking out tomo at this point.”
While more than 15 hospitals and imaging facilities in the Boston area have acquired the tomosynthesis machines from Hologic, some are holding back because insurance companies do not yet typically reimburse for the 3-D scan. Some patients get charged $50 for the additional imaging test, while some facilities including Mass. General have chosen to absorb the cost.
“The results of the JAMA study are very significant when translated into real world numbers,” said a statement released by Hologic. “If 3D was the standard of care in the U.S., more than 500,000 women each year would not have to undergo the anxiety or lost work time of a recall.”
The cost of the 3-D machine is $400,000 to $450,000, but many imaging centers have Hologic machines that can be upgraded to 3-D for $125,000 to $150,000, according to Rachael Bennett, a clinical analyst at MD Buyline, a clinical and technology research firm that serves health care systems.
“There’s been an enormous amount of interest from hospitals in purchasing this technology,” Bennett said.
The government will decide next month whether to add tomosynthesis to its list of procedures reimbursable by the Centers for Medicare & Medicaid Services.