Effect of Three Decades of Screening Mammography on Breast Cancer
Embargoed until Wednesday, November 21 at 5 PM ET
Lebanon, NH (Nov. 19, 2012) – In the last three decades, researchers estimate more than a million women have been overdiagnosed with breast cancer. And despite all the screenings with mammograms, there has been no change in the incidence of metastatic breast cancer and little decrease in the rate that late-stage cancer is found.
In a study published in the New England Journal of Medicine Nov. 21, Dr. Archie Bleyer of
St. Charles Health System in Bend, Ore., and Dr. H. Gilbert Welch of The Dartmouth Institute for Health Policy & Clinical Practice in Lebanon, N.H., said that nearly a third of all newly diagnosed breast cancers have been overdiagnosed and screening, at best, is having only a small effect on the mortality rate from breast cancer.
The good news is that fewer women are dying from breast cancer, but the researchers concluded that this is due largely to better treatment, not screening.
This study takes a “different view,” the researchers said, in that it uses national data over a period of three decades and details what has actually happened since the introduction of screening mammography. “It does not involve a select group of patients, a specific protocol, or a single point in time,” they said.
The researchers were interested in learning how well mammography was working in terms of basic screening principles. To reduce the rate of death from cancer there are two prerequisites: First, screening must advance the time of diagnosis of cancers that are destined to cause death. Second, it must cause fewer late-stage cancers to be found since each person diagnosed earlier via the first requisite is not diagnosed later with worse cancer.
Unless late-stage cancer is reduced, any observed improvement in cancer deaths must be due to something else and for breast cancer that would primarily be better treatment, they said.
The introduction of screening mammography in the U.S. has been associated with the doubling in the number of cases of early-stage breast cancer that are detected each year – an absolute increase of 122 cases per 100,000 women. But, the rate at which women present with late-stage cancer has decreased by 8 percent, an absolute decrease of 8 cases per 100,000 women.
The researchers estimated that breast cancer was overdiagnosed in 1.3 million U.S. women in the past 30 years. In 2008 alone, they estimated that breast cancer was overdiagnosed in more than 70,000 women, accounting for 31 percent of all breast cancers diagnosed.
“And although no one can say with certainty which women are overdiagnosed, there is certainty about what happens to them: they undergo surgery, radiation therapy, hormonal therapy for five years or more, chemotherapy, or (usually) a combination of these treatments for abnormalities that otherwise would not have caused illness.”
What does this mean for women 40 years of age and older? The researchers said it means women really do have a choice about breast cancer screening. The benefit of mammography in lowering the death rate is considerably smaller than has been previously recognized, and the harm of overdiagnosis considerably larger.
“Women should recognize that our study does not answer the question ‘Should I be screened for breast cancer?’” the researchers wrote. “However, they can rest assured that the question has more than one right answer.”
Bleyer and Welch used trend data from the CDC’s National Health Interview Survey on the proportion of women 40 years of age or older who underwent screening mammography. They also used trend data from 1976 through 2008 on incidence and survival rates from the nine long-standing Surveillance, Epidemiology, and End Results (SEER) areas. These SEER data sets accounted for approximately 10 percent of the U.S. population. Annual estimates of the population of women 40 years of age or older were obtained from the U.S. Census.
Dr. Archie Bleyer is chair, Institutional Review Board, St. Charles Health System, Central Oregon, and clinical research professor, Department of Radiation Medicine, Knight Cancer Institute at Oregon Health & Science University.
Dr. H. Gilbert Welch is professor of Medicine at The Dartmouth Institute for Health Policy & Clinical Practice and of Community & Family Medicine at the Geisel School of Medicine at Dartmouth, professor of Business Administration (adjunct) at the Tuck School of Business, and professor of Public Policy (adjunct), Dartmouth College.
The Dartmouth Institute, Lebanon, N.H., Annmarie Christensen, (603) 653-0897, cell (802) 249-8795, email@example.com
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Knight Cancer Institute, Portland, Ore., Elisa Williams, (503) 494-4530, (971) 344-5441, email@example.com