A rapid response from Karsten J Jorgensen and Peter Gotzsche, the Nordic Cochrane Centre, to Weedon-Fekjær et al’s population study, ‘Modern mammography screening and breast cancer mortality, 17 June 2014. BMJ 2014;348:g3701 is not only enlightening, but backed by robust research.
‘While a screening effect on population mortality rates is initially “diluted” by deaths from breast cancers detected before screening was introduced, this cannot explain the lack of a visible effect after 17 years. By then, practically all breast cancer deaths would be from cases detected within the screening era. A graph should show two increasingly separating lines if screening had any worthwhile effect, but this is not the case’, they explain.
‘The fall in breast cancer mortality started around 1990 in all countries, which was when effective treatments were introduced, and the rate of decline was about the same in all countries. When results of observational studies seem too good to be true, we should look for other explanations.’
‘Whatever the effect of screening on breast cancer mortality, it is the wrong outcome. Treatment of healthy overdiagnosed women increases their mortality, which means that total mortality is the most meaningful outcome’.
NB Critical research analysis is difficult, and can be impossible for most people, including doctors, and conflicting information makes understanding even more difficult. But in the Cochrane Research Centre we have access to the gold standard.