A cancer stem cell. (UCLA )
The question seemed simple enough: Should women in their 40s be advised to get routine mammograms in the hopes of catching breast cancers while they are still small and, presumably, easier to treat? But the more an expert panel of doctors, nurses and preventive health specialists studied the data, the harder it was to come up with an answer.
Without screening, 3.5 out of every 1,000 women ages 40 to 49 will die of breast cancer in the next 10 years; regular mammography can reduce that number to 3. The panel calculated that to save one life among women in this age group, 1,900 women must be screened annually for 10 years. The other 1,899 women will receive no benefit from mammography over that period, though they will field 1,330 call-backs for reassessment and 665 breast biopsies, and eight of them will be diagnosed with cancers whose prognosis will not be altered by detection via mammogram — either because they would never become dangerous or because they are so aggressive that there's little to be done.
Ultimately, the U.S. Preventative Services Task Force decided in November 2009 that whether the benefits are worth the risks is a value judgment each woman should make for herself.
"When it comes down to values, that's when you want to put it in the hands of patients and their doctors," says task force member Ned Calonge, a physician who at the time was the chief medical officer of the Colorado Department of Public Health and Environment.
The panel wrestled with the language, finally deciding to recommend "against routine screening mammography" for women in their 40s. The intention was to emphasize the word "routine," but instead people focused on the word "against," and "no one got beyond that," Calonge says.
Confusion and outrage ensued. The American Cancer Society, Susan G. Komen for the Cure and the American Congress of Obstetricians and Gynecologists criticized the task force recommendations and continued to call for annual or biennial mammograms for women in their 40s, in line with the panel's guidelines from 2002. The National Breast Cancer Coalition and other organizations that stood by the task force faced fierce criticism, and task force members found themselves defending their decision before a congressional committee.
More than a year later, the dust is still settling. Three new studies examining the benefits of mammography have been released since the guidelines were revised, but they have only added to the confusion.
A study published last March in the journal BMJ compared women who lived in a region of Denmark where mammography screening was offered to those who lived in areas without screening and found no reduction in breast cancer deaths associated with mammography.
A similar study published in the journal Cancer in September compared breast cancer death rates in women from a region of Sweden with a public mammography program to those in an area without the program and found that deaths were 29% lower in the area with a screening program.
Yet another study that month, published in the New England Journal of Medicine, compared breast cancer deaths in women taking part in a Norwegian national screening program with those who were not screened, looking at mortality rates in those areas before and after the screening program began. This study found that breast cancer deaths had dropped since the mammography program began. But it calculated that most of the improvement was attributable to increased breast cancer awareness, which led women to seek treatment right away for any lumps or bumps they discovered, and new treatments. The contribution of routine mammography to the reduction may have been as small as 2%.
How could these studies yield such contradictory results? The answer is simple, says Dr. Heidi Nelson of Oregon Health and Science University in Portland, who led a research team that compiled evidence for the task force. All of these studies were observational, meaning they were done on groups of women who either chose to get mammograms or didn't — and there can be very real differences between those two groups.
"If you just look at the women who show up for mammography, you're looking at a biased sample of people," Nelson says: Women who choose to get mammograms are usually healthier and more health-conscious than those who skip the screenings. For this reason, the task force based its recommendations on the evidence from trials that took groups of women who were as similar as possible and randomly assigned them to either a screening or no-screening group.
"We had eight randomized trials. That's as good as it gets in our line of research," Nelson says.