Are Mammograms a Useful Screening Tool?

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A Candadian study published in April 2014 weighs in, once again, on the value of screening mammograms.  In this study, no difference in death rate was found in the screening group compared with the control group.  The Cochrane group(Cochrane.org), has also weighed in on this question.  This is a non-profit group that evaluates randomized controlled trials in an attempt to make impartial recommendations on medical practices.  As I understand it, they do not receive funding from sources that would influence their recommendations.  The Cochrane group gives the following statistics.  If 2000 women were screened with mammograms yearly for 10 years,  200 would need additional testing such as biopsy or additional mammograms.  Out of those 200, 11 women would be diagnosed with breast cancer.  However only one of those eleven women would receive any improvement in life expectancy.  The side effects, and adverse outcomes to the other 10 women who received treatment without benefit were not quantified.  This seems to me to be the fundamental question.   How do we decide whether a screening test is worth using, if we do not accurately determine the extent of adverse effects on the treatment of the group of patients who don’t benefit from earlier diagnosis?   If you are interested in reading a review article,  about this, it can be found at:

http://fivethirtyeight.com/features/are-mammograms-worth-it/

One other article from the New England Journal of Medicine in 2012 showed a graph of breast cancer incidence in women older than forty.  As the use of mammography increased over the past 30 years, there was an increase in incidence of early stage cancers.  In other words, we diagnosed more early stage breast cancers for doing more mammograms.  Late stage cancers were not diagnosed more frequently.  In women under 40, there was no improvement in breast cancer diagnosis.  The second graph shows that there has not been much change in the development of late stage breast cancers during this time period when mammogram usage became more commonplace.  The hope with mammography has been that earlier diagnosis would prevent more deaths from breast cancer.  This does not to appear to be happening.  The authors of this article conclude:

“Despite substantial increases in the number of cases of early-stage breast cancer detected, screening mammography has only marginally reduced the rate at which women present with advanced cancer. Although it is not certain which women have been affected, the imbalance suggests that there is substantial overdiagnosis, accounting for nearly a third of all newly diagnosed breast cancers, and that screening is having, at best, only a small effect on the rate of death from breast cancer.”

The full article with the graphs can be seen at:    http://www.nejm.org/doi/full/10.1056/NEJMoa1206809

A youtube video summarizing this  recent 2016 study can be seen at:https://www.youtube.com/watch?v=IwoIBTJD1VQ

The American Cancer Society recommends screening mammography starting at age 40.  This group receives funding from industry.  The US Preventive Health Services task force changed its recommendations last year to recommend screening for women 50 and older, on an every other year basis.  There remains a great deal of disagreement about the best approach to this question, however the data is not compelling for the routine use of mammography for screening.

Bruce Gollub MD

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