Dr. Marla Shapiro: Making sense of conflicting studies about mammograms
Published Tuesday, November 27, 2012 7:53AM EST
Last Updated Wednesday, November 28, 2012 7:30AM EST
Last week, a large 30-year study in the New England Journal of Medicine was reported fueling the mammogram controversy. The study looked at the effects of mammography over 30 years in the U.S. and found a 100 per cent rise in the detection of early stage breast cancers, but they believe that up to one-third may be cancers that would never grow.
As was pointed out, when we look for early forms of cancer, we know that some of the things that pathologists call cancer will never bother patients. As well, mammograms had almost no effect on the number of late-stage cancers picked up. There have been many studies that say many women are undergoing treatment without reason.
Not everyone agrees, however, with these findings. As experts in breast screening note -- how do we know which cancers are actually harmless?
An independent U.K. panel presented its review of the benefits and harms of screening reported in the Lancet. The main questions were how large the benefit of screening is in terms of reduced breast cancer mortality and how substantial the harm is in terms of over diagnosis, which is defined as cancers detected at the time of screening that would not have otherwise become clinically apparent in the woman's lifetime.
An independent panel was convened to reach conclusions about the benefits and harms of breast screening on the basis of a review of published work, as well as oral and written evidence presented by experts in the subject. They found a risk reduction of breast cancer mortality for women invited to screening, compared with controls, of 20 per cent and estimates of the excess incidence of 11 per cent. Results from observational studies support the occurrence of over-diagnosis, but estimates of its magnitude are unreliable.
The panel concluded that screening reduces breast cancer mortality, but that some over-diagnosis occurs. They found for every 10,000 U.K. women, aged 50, invited to screening for the next 20 years, 43 deaths from breast cancer would be prevented. They also found that a 129 cases of breast cancer, both invasive and non-invasive, would be over-diagnosed; that is one breast cancer death prevented for about every three over-diagnosed cases that were identified and treated. They also showed that many women feel that accepting the offer of breast screening is worthwhile, which agrees with the results of previous similar studies.
Now, yet another study was reported today. Researchers assessing the impact of revised guidelines for screening mammography issued by the U.S. Preventive Services Task Force (USPSTF) found evidence that the new recommendations may lead to missed cancers and a decline in screening. Two studies were presented today at the annual meeting of the Radiological Society of North America. Routine screening mammography has traditionally been recommended by both the USPSTF and the American Cancer Society for all women over the age of 40. But in 2009, the USPSTF issued controversial new guidelines recommending routine screening with mammography every two years for women between the ages of 50 and 74. Researchers analyzed the impact of the new guidelines on women between the ages of 40 and 49 and the Medicare population.
The inconsistent information is very confusing for everyone. For one study, a team of researchers analyzed data on screening mammography at New York Presbyterian Hospital Weill Cornell Medical College between 2007 and 2010. Over the four years, 43,351 screening exams were performed, which led to the detection of 205 breast cancers.
Nearly 20 per cent of cancers detected with screening mammography were found among women in their 40s in this group. The author notes that it seems unacceptable to potentially miss nearly 20 per cent of the breast cancers that we are identifying. This would represent a substantial degree of under-diagnosis.
Of the women screened in the study, 14,528, or 33.5 per cent, were between the ages of 40 and 49. Of the 205 breast cancers detected, 39 women (19 per cent) were found in the 40-49 age group. Of those cancers, more than 50 per cent (21 of 39) were invasive. Only three of the women between the ages of 40 and 49 diagnosed with cancer had a first-degree relative with pre-menopausal cancer.
In the second study, a team of researchers analyzed data from The Medicare Part B Physician/Supplier Procedure Summary Master Files for 2005-2010. They calculated the following annual utilization rates for screening mammography per 1,000 female beneficiaries. The compound annual growth rate for screening mammography utilization was 0.9 per cent, compared to a 4.3 per cent decline in the utilization rate from 2009 to 2010. Clearly there was a significant drop in utilization.
So, where does this leave us? I believe it means transparent discussions about the risks and benefits of screening and a collaborative decision between patient and physician.