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Radiology Society of North America: Annual Breast Cancer Screening Beginning at Age 40 Reduces Mastectomy Risk

December 5, 2010

Annual screening mammography reduces the risk of mastectomy in women ages 40 to 50, according to a press release  from the Radiology Society of North America.  These claims are based on results from a study conducted at the London Breast Institute where investigators reviewed the clinical data available on women ages 40 to 50 that had been diagnosed with breast cancer and treated at the Institute between 2003 and 2009.  Merely 156 women fit the inclusion criteria, and of the 156, only 16 women had mammography one year previously.  The investigators proceeded to compare the mastectomy rate (as opposed to breast conserving surgery) of these 16 women to the rate of women who had not had a mammogram within the past year (n=140). 

“The results of our study support the importance of regular screening in the under-50 age group and confirm that annual mammography improves the chances of breast conservation should breast cancer develop,” said lead author, Dr. Nicholas Perry.  These claims are based on results that women who had a prior mammogram within the past year had a mastectomy rate of less than half that of the other women (19% vs. 46%).  While these results may be statistically significant, they are based on a comparison of the mastectomy rate of merely 3 women and 64 women with and without mammography within the past year, respectively.  Such results do not infer that mammography reduces the mastectomy rate.  Since this study was retrospective in nature, we do not know if the two comparison groups were similar with respect to other factors which influence breast conservation following diagnosis.  For example, were the biological characteristics of the tumors similar in the two comparison groups? 

According to Perry, the investigators were “surprised at the degree of benefit obtained from yearly screening in this age group.”  This is an example of yet another study failing to measure, or even simply acknowledge, the harms associated with screening women under 50.