Breast cancer detection in an institution. Is mammography detrimental?

The poor results of the National Breast Screening Study of Canada regarding the screening of women aged 40-49 have been interpreted to suggest that mammography might be detrimental. Our comparison of women who had mammography and had their cancers detected by mammography with women who did not have mammography and had palpable cancers suggest that this is not the case. There is no detrimental effect; rather, the use of mammography results in an improvement in survival. The poor results of the National Breast Screening Study likely are due to the unbalanced allocation of women with advanced cancers to the screened group, the poor quality of the mammography in the trial, and an insufficient sample size.