March Spotlight – Radiology: Discredited 1980s screening mammography studies vs. the reality of 2014

By Emma Simpson, MD, Interim Chair, Department of Radiology

 Many of you are aware of the controversies surrounding screening mammography guidelines.

 The American Cancer Society and all the major clinical societies involved in the diagnosis and care of breast cancer agree to the following guidelines:

  • Yearly mammograms are recommended starting at age 40 and continuing for as long as a woman is in good health
  • Clinical breast exam (CBE) about every 3 years for women in their 20s and 30s and every year for women 40 and over

 Since the US task force issued its controversial guidelines for screening mammography, there have been multiple discussions of the issue in the lay press and medical journals.  The most recent medical article appeared in British Medical Journal (see http://dx.doi.org/10.1136/bmj.g366 ) and raised more doubts as to the benefit of screening mammography.  

 What readers are often not made aware of are the problems with the original study that these conclusions are based on. The British  article is a rehashing and reanalysis of the previously discredited Canadian National Breast Screening Study (CNBSS) from the 1980s.  Following patients for a longer time in a flawed study does not fix nor improve the problems with the study (see Q&A with Dan Kopans, MD, FACR, FSBI Re: Canadian Study). Some of the major flaws of the original study (see The Canadian National Breast Screening Study: A Canadian Critique) include:

  • It was done with old, second hand, poor quality equipment
  • It was read by radiologists with no special training in mammography.  
  • The randomization of patients was not blinded; the patients underwent a breast exam prior to randomization, and a significantly higher number of patients with advanced, lymph node positive breast cancers were “randomized” to the screening arm of the study than to the control group. 
  • There was no agreed upon threshold for intervention, and some of the mammographically detected breast cancers that were not palpable were not treated until they became palpable. 

Needless to say, there have been many retorts by multiple medical societies including the Society of Breast Imaging.

The fact that mammography saves lives has been proven over and over again by multiple studies.  And the reduction in mortality is only the beginning of the story.  The life-altering morbidity associated with treating later stage cancers includes  disfiguring surgery, axillary dissection, and  debilitating  chemotherapy. This morbidity can be avoided with early detection and treatment of an earlier stage tumor. This aspect is never addressed in the BMJ article and others like it.   

 As far as the controversy over when to begin mammography is concerned, more years of productive life are saved when cancer is detected in a woman aged 40-49 than at any other age. This is during a time when women are raising a family and pursuing careers.  Less morbidity and less complicated treatments of earlier stage tumors have a tremendous impact on quality of life, and this must be taken into account.  

 To put the cost of mammography in perspective, take a look at this comparison: the cost per life-year saved with screening mammography from age 40-79 is $18,800; the cost per life-year saved with seat belts and air bags is $32,000. (Tengs TO, Adams ME, Pliskin JS, et al. Five-hundred life-saving interventions and their cost-effectiveness. Risk Anal 1995; 15:369-390.)

 

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