Screening without evidence of efficacy

Screening of unproved value should not be advocated

Screening has intuitive appeal. Cancer, for example, causes a quarter of all deaths, and a doctor does not diagnose many incurable cancers without wanting some means of bringing forward the diagnosis. Before any screening for cancer is introduced, however, large randomised trials with mortality end points should be conducted to establish and quantify any benefit. But there is a view that there must be some gain from earlier diagnosis; awaiting trial results is a needless delay. The scientific rigour applied to other areas of medicine may not always be applied to screening.

Cancer of the prostate is an example. The serum concentration of prostate specific antigen can predict mortality from prostate cancer.1^–4 There are no published randomised trials that the earlier detection improves prognosis, yet in the United States and Italy a third or more of healthy men aged over 50 have had prostate specific antigen measured in the past two years.4 5 In Britain, on the other hand, only 5% have,5 and the available evidence on prostate specific antigen testing in reducing mortality indicates that the British are right to reject it.

A problem with using prostate specific antigen (or any chemical produced by a cancer) as a marker for screening is that the serum concentration will increase …