Sunday, October 10, 2010

New study out of Norway: calling mammograms into question

A new study came out of Norway and appeared in the New England Journal of Medicine recently, casting doubt on the benefit of mammograms.  It analyzed data on over 40,000 women, aged 50-69yrs, over a nine year period, and found that mammographic screening alone accounts for a modest 10% decrease in breast cancer death.

Based on these results, some naysayers may want to denounce the use of regular mammograms to help the battle against breast cancer.  But I would disagree.  As with any study, we need to consider the possibilities.

Partial list of risk factors for breast cancer

  • Genetics: BRCA-1 and BRCA-2
  • Family history
  • Age: increased risk with age
  • Obesity
  • Excessive alcohol use
  • Lack of physical exercise

This list is hardly complete, but I want to stress a point: looking at one group of women leaves open many possibilities.  
  • Do the BRCA gene mutations run in the Norwegian population?  Since it does have a prevalence in the American population, this is an important question.
  • Obesity: a very clear risk factor; America has a definite problem with obesity, does Norway?
  • Excessive alcohol use: is this prevalent in Norway?
  • Lack of physical exercise: America is not known as a very active nation, how does Norway compare?

Those four questions alone could drastically change the outcome of the study.  If the population is less likely to develop breast cancer in general, then mammograms will diagnose breast cancer less frequently.  We also have to consider the presentation of breast cancer: how do lifestyle and genetics affect the radiographic presentation of breast cancer?  This too could affect the outcome of the study.

Other studies contradict the Norwegian study, and I have to agree with the contradictions, although on different grounds.  Mammography does not expose a woman to significant levels of radiation.  What significant disadvantages exist?  

Even going by this Norwegian study: 10% more lives saved is 10% more than zero.

For the record: One study is hardly enough to change a well practiced medical routine.

ResearchBlogging.org
Mette Kalager, M.D., Marvin Zelen, Ph.D., Frøydis Langmark, M.D., & Hans-Olov Adami, M.D., Ph.D. (2010). Effect of Screening Mammography on Breast-Cancer Mortality in Norway NEJM, 1203-1210

http://www.cancer.org/Cancer/BreastCancer/DetailedGuide/breast-cancer-risk-factors

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