Recent research questioning the value of mammography in reducing deaths from breast cancer for women in their 40s and 50s has reignited a long-running debate over the value of routine screening. Noted breast imagers and national radiology organizations strongly dispute the findings and contend that the study’s conclusions are based on flawed research.
The Canadian National Breast Screening Study (CNBSS) study, published online Feb. 11 in the British Medical Journal, is a 25-year follow-up of nearly 90,000 Canadian women, ages 40 to 59. Researchers compared outcomes in women who underwent screening mammography with those who didn’t and found that the cumulative mortality from breast cancer was similar between the two groups and that screening did not reduce breast cancer death beyond the effects of physical exams or usual care from their doctor. These results echo the preliminary findings of the CNBSS published in the 1990s.
“We were initially surprised by the results of the first report, and as we continued to follow the women we thought we might see a favorable impact for mammography later on,” said principal investigator Anthony B. Miller, M.D., professor emeritus at the Dalla Lana School of Public Health at the University of Toronto. “But 16 years later, we continue to see the same long-term effect.”
Dr. Miller and colleagues randomly assigned patients to the mammography or control group. Those in the mammography group had a mammogram every year for five years; the control group was not screened. Women ages 40–49 in the mammogram group and women ages 50–59 in both groups also received annual clinical breast exams. Women ages 40–49 in the control group received one clinical breast exam and typical care from their doctor. After five years, women in the study received care from their regular doctor, which could include mammograms at their doctor’s discretion.
During the five-year screening period, 666 invasive breast cancers were diagnosed in the mammography group (nearly three-fourths of them detected through screening), with 180 of those cancers becoming fatal within 25 years. In the control group, 524 invasive breast cancers were diagnosed—171 of them fatal within 25 years.
Because more cancers were diagnosed by mammography but essentially the same number of women died of breast cancer, researchers concluded that mammography was overdiagnosing breast cancer and they recommended that annual breast cancer screening through mammograms be reevaluated.
Many in the breast imaging community view the new research as deeply flawed and say it raises the same problems as the results of the first study published in the 1990s. Deficiencies cited include the study design, the quality of the mammograms and the lack of training in those who performed and interpreted the images.
“It’s déjà vu all over again,” said Gary J. Whitman, M.D., professor at the University of Texas M.D. Anderson Cancer Center in Houston and a member of the RSNA News Editorial Board. “The major deficiencies present in the study make it difficult to look at it in anything other than a very critical light.”
ACR and Society of Breast Imaging (SBI) issued a joint statement characterizing the research as “an incredibly misleading analysis based on the deeply flawed and widely discredited Canadian National Breast Screening Study.”
ACR and SBI officials suggested that changes in screening recommendations would place a great many women at increased risk of dying unnecessarily from breast cancer, pointing to the inclusion of women with palpable lumps at the beginning of the study period as a major flaw that may have skewed the results.
That concern is shared by Debra Copit, M.D., director of Breast Imaging at Einstein Medical Center in Philadelphia and a member of the Breast Imaging Subcommittee of the RSNA Scientific Program Committee and the Public Information Committee. “The whole point of screening mammography is to detect breast cancer before it’s palpable,” Dr. Copit said. “In this study, 68.2 percent of cancers found in the group screened with mammography were palpable, which tells me that the study is flawed.”
In response to the criticism, Dr. Miller noted that two U.S. epidemiologists endorsed the study design. He disputed the contention that women with advanced cancer were included in the mammography arm of the study but not the control arm and defended the quality of the mammograms.
But Dr. Copit pointed out that the mammograms used in the study did not include the more expansive mediolateral oblique view and that patients didn’t receive yearly mammograms.
“Despite excellent follow-up, they didn’t do correct views or screen every year,” she said. “Therefore, the conclusions are difficult to interpret or validate.”
Dr. Miller responds: “In fact we did screen every year, and the views we used were standard in North America in 1980 when we started the trial,” he said. “We changed to include the mediolateral oblique view in 1984 from the previously standard mediolateral view, with the cranio-caudal view used as well throughout.”
The Canadian study has enlivened an argument over mammography that has been ongoing since screening recommendations first came into focus in the 1980s. Early guidelines grew out of results from large, randomized control trials that tied mammography to a significant reduction in breast cancer-related mortality, including the Two-County Study of more than 130,000 women that began in Sweden in 1977. Swedish researchers found a 31 percent decrease in mortality among women from the group who were screened compared with those who had no screening.
That study, which published its 29-year follow up in 2011, provides more useful data on screening mammography, according to Mary C. Mahoney, M.D., professor of radiology at the University of Cincinnati Medical Center and director of Breast Imaging at Barrett Cancer Center in Cincinnati. Dr. Mahoney serves as the RSNA Board Liaison for Publications and Communications.
“The Two-County study was better designed and more truly randomized than the Canadian study,” Dr. Mahoney said.
Based on results from the Two-County study and other research, the American Cancer Society recommends annual screening for women starting at age 40. Other groups, like the U.S. Preventive Services Task Force and the Canadian Cancer Society, say screening should start at age 50 and take place once every two years instead of annually.
Those recommendations are counterintuitive, according to Dr. Copit, a breast cancer survivor whose cancer was detected by mammography when she was in her forties. “Women in their forties tend to have faster-growing, more aggressive cancers,” she said. “They need to be screened more often, not less often.”
In addition, earlier detection usually requires less aggressive treatment that is better tolerated by patients, according to Dr. Mahoney.
The recent Canadian National Breast Screening Study has reignited a discussion over mammography that has been ongoing since screening recommendations first came into focus in the 1980s.
The recurring argument over screening is not likely to abate anytime soon, even with improvements in technology like tomosynthesis and the addition of supplemental imaging with ultrasound and MR in women with mammographically-dense breasts.
“Mammography comes up often as healthcare dollars get tighter and tighter and people start looking for places to cut back,” Dr. Copit said.
“There seems to be a persistent group of researchers who are opposed to mammography,” Dr. Mahoney added. “I can’t name one other test that has undergone the rigor that mammography has.”
Breast imaging experts do not expect the Canadian study to impact existing screening recommendations or insurance coverage. In the U.S., most states mandate coverage for regular screenings for women 40 and older and laws would require action by state legislatures to be changed.
“There are good data showing that screening mammography decreases mortality for patients 40 to 49, as well as those ages 50 to 59,” Dr. Whitman said. “Most major organizations recommend annual screening, and over time as we get more follow-up data, the research supporting it will become even stronger.
“It’s clear to me, after 20 years of practice, that we should start screening at age 40 and continue every year,” Dr. Copit said. “A more interesting question is, at what age do we stop screening?”
Richard Dargan is a writer based in Albuquerque N. M., specializing in healthcare issues.
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