The screening mammography paradox: better when found, perhaps better not to find

In this issue, Wishart et al (2008) address whether ‘screen-detected breast cancer confers additional prognostic benefit to the patient, over and above that expected by any shift in stage at presentation’. Their conclusion is affirmative. Although this observation is not new and indeed is increasingly understood and accepted by the research community ( Joensuu et al, 2004 ; Shen et al, 2005 ), their study is an important confirmation. One application of the observation has been in statistical models that make inferences about the relative contributions of screening and adjuvant therapy to the decrease in breast cancer mortality that has occurred over the last 20 years in the United States (and in other countries as well) ( Berry et al, 2005 , 2006b ; Fryback et al, 2006 ). A conclusion of these models is that, taking therapy into account, the observed breast cancer incidence and mortality would be inconsistent unless some cancers preferentially detected by screening mammography had, in the terminology of one study ( Fryback et al, 2006 ), ‘limited malignant potential’.