September 23, 2010, 10:18 AM ET
By Katherine Hobson
Study: Mammograms Save Lives — Just Not As Many As Expected.
The debate over the value of mammograms, which really kicked into gear when the U.S. Preventive Services Task Force issued its controversial screening recommendations last fall, is still raging. And providing new fodder for discussion is a study just published in the New England Journal of Medicine that suggests women aged 50 to 69 are indeed less likely to die from breast cancer if they undergo screening — but not by as much as researchers had expected.
The study looked at breast cancer deaths in Norway as a screening program was rolled out, in a staggered fashion, across the country. At the same time that mammography screening was introduced into a county, so was a coordinated, multidisciplinary approach to treating women who developed the disease. (Note the screening program did not include the age group that’s really controversial in the U.S., women aged 40-49.)
The study looked at breast cancer mortality rates in areas that introduced the screening and coordinated treatment compared to those in areas that didn’t. It also looked at how mortality rates changed over time, even before any formal program was in place. Those historical data show how mortality was changing for other reasons — such as better treatment options or increased awareness on the part of patients and doctors — study co-author Marvin Zelen, a scientific statistician at the Harvard School of Public Health and Dana-Farber Cancer Institute, tells the Health Blog.
The screening program was associated with a 10% decline in mortality, the researchers found. (Zelen says they expected something more along the lines of 30%.) That’s about a third of the total reduction in mortality seen over the years. Moreover, it’s not clear how much of that was due to mammography alone, given the more coordinated care that was also part of the program.
The study is important because it offers a more current picture of the benefits of mammography, Zelen says. It’s possible that the screening test was more valuable many years ago, when it mattered more than it does now whether breast cancer was caught at stage 1 or stage 2. Due to newer therapies, that distinction is less important than it was 20 years ago, he says.
In a statement, Otis Brawley, the chief medical officer of the American Cancer Society raises the question of whether the smaller benefit seen in this observational study compared to older randomized trials is due to a shorter follow-up period. (Zelen says the shorter follow-up is because it began at diagnosis, not when the screening program started.)
Zelen says women need to weigh the benefits of screening (a lower chance of dying from breast cancer, at least in this age group) against possible risks. As an accompanying editorial notes, those include false alarms and unnecessary biopsies, as well as the “less frequent but more worrisome” problem of needlessly treating cancer found via mammogram that never would have amounted to anything if it went undetected. If you take the approach of “minimizing the maximum risk,” as Zelen says, that suggests being screened.
But “we have to make decisions about our health on the basis of what’s important to us,” he says.
Because “mammography is not perfect and will not detect all breast cancers, and since a small percentage of breast cancers are diagnosed in women who are younger than the age when screening is recommended, it is important for all women to maintain a heightened awareness about breast symptoms,” Brawley says.