Does your head ever swim trying to keep up with all the new studies on health issues? Based on a review of scientific studies, in November 2009 the U.S. Preventive Services Task Force recommended that most women under 50 did not need routine screening and that women over 50 could be screened less frequently. Part of their concern was that the cost of mammograms both in money and anxiety is not worth the number of lives that are saved. According to their figures, it was necessary to screen 1,000 women to save one life.
Yesterday on the news I heard that a new study found that mammograms reduce breast cancer deaths by 30%. Wow! What a difference!
In this study published in Radiology, researchers, led by Dr. Stephen Duffy of Queen Mary, University of London, found that one breast cancer death can be prevented for every 414 to 519 women screened, much better than the 1,000 to 1,500 women estimate in the earlier studies. The study enrolled 1,300 Swedish women and looked at the differences between those who had mammograms during a seven year period and those who did not. Why the discrepancy between this and earlier research?
One important factor is that this study has been a long-term one. It has followed women for 29 years and found that as time goes by, the benefits of mammogram screening grow. This may be because breast cancer tends to be a slow growing disease. If a study measuring mammogram benefits ends after five years, it will miss the woman who develops a palpable tumor six years after a mammogram might have found that tumor when it was tiny. Because this study also looks at death rates, not just incidence of disease, the longer time period can take into account women whose cancers metastasize and who die many years after initial diagnosis and treatment.
The study may actually underestimate the current benefit of mammograms because thirty years ago the equipment was not as effective. However, it does seem to answer an important public health question: do screening mammograms on large populations of apparently healthy women save lives? Yes, says this study.
Because the researchers did not break down their results by age, the study will not help answer one current controversy. What is the most effective age to begin mammograms?
These big studies help doctors evaluate big public health issues, but they do not necessarily help a patient decide what she should do personally. This will remain a decision between a woman and her doctor based on her own medical history and breast cancer risk factors. For people involved in advocacy work, the study will bolster their efforts to ensure funding for mammograms as a part of the effort to bring down the death rate from breast cancer.
When you hear about apparently conflicting studies that might affect you, how can you evaluate them without a science background? Generally speaking, the larger the study and the longer it lasts, the more valid it is likely to be. Also ask who funded the study. With government cut backs in scientific funding, much research these days is funded by people who make the product being evaluated. So a study funded by a neutral party is less likely to be tainted by bias towards the folks who gave the money.
If you get a chance, consider being part of a study. I recently volunteered for a large, long-term study of the health of people in my county. It took about a half an hour to give them blood samples and to fill out a questionnaire about my health history. The scientists intend to track us for many years to come. They don't know what they will find, but the results might be as dramatic as the Framingham, Massachusetts study that discovered the risk factors for heart disease or this Swedish study that provides solid evidence that mammograms save lives.
Published On: June 29, 2011