Does Mammogram Risk Outweigh Benefit?
Value of Early Breast Cancer Screening Questioned
Oct. 14, 2003 -- For most women under 50, annual mammograms offer a small benefit. A growing number of researchers say this benefit may not outweigh the risks.
One of those researchers is Cornelia J. Baines, MD, professor emerita at the University of Toronto and co-leader of Canada's largest clinical trial of breast-cancer screening. Her editorial in the Oct. 15 issue of the Journal of the National Cancer Institute argues that women -- particularly those aged 40-49 -- are urged to get mammograms without being told of the risks.
One of those risks may be the "screening paradox" seen in women who start getting annual mammograms before the age of 50.
"There is a consistently observed increase in breast cancer deaths in the first 10 years of screening," Baines tells WebMD. "It is consistent, it occurs across time, and it occurs across countries."
There's a benefit to early screening. But it's much smaller than most women realize.
"If you truly look at the benefit to be obtained for women in the 40-49 age group, it is very small and takes a long time," Baines says. "It is a 9% decrease in cancer deaths after 16 years."
Meanwhile, she notes, the risk of death from breast cancer in the third year of screening is more than twice as high for women who get mammograms as for women who don't.
Is It Real?
The trouble with the screening paradox is that it might not be real, says Alfred O. Berg, MD, chairman of the department of family medicine at the University of Washington. Berg led the U.S. Preventive Services Task Force that rigorously evaluated the evidence for and against breast cancer screening.
"I don't agree with Dr. Baines that every study shows this," Berg says. "We are not sure the observation that she and others have made is actually there. ... We would probably judge the evidence as weak, because none of the studies were formally designed to look at this question."
Berg says it would be interesting to look into the questions raised by the screening paradox. And that's all Baines asks. But it's never been done.
"It is a shame this very clear message has been ignored for so long," she says. "We first reported this in the 1980s. If people had tried to get to the bottom of this, we might be further along than we are now. ... I want someone to tell me they will look into this paradox. To say, yes, that is a way we will get around to learning more about breast cancer."
How could mammograms cause breast cancer? Baines doesn't think it's the mammograms themselves. Women who get screened find small tumors sooner. This leads to earlier surgery. Some of these tumors might not really be dangerous. But removing them might be, animal studies suggest.