Two of the responses to an editorial by Julietta Patnick, Director NHS Cancer Screening Programmes, (Benefits of screening take years to appreciate -bmj 16 January 2013 – BMJ 2013;346:f299) are especially noteworthy. One, from Hazel Thornton, explains the difference between risks and harms, and points out that ‘harms’ are not mentioned in this article, even though breast screening has been shown to inflict harm on more people than it helps.
‘* A risk is “the probability of harm taking place. It is not possible to directly compare benefits and risks because one is an outcome while the other is the probability of an outcome.” ’
The other from GP, Dr Jonathan D Sleath, says he regularly talks to patients about breast screening, but the risks are not immediately evident to them. ‘The risks associated with overdiagnosis are glossed over in the NHS breast cancer screening leaflet with the single phrase “Screening may find cancers which are treated but which may not otherwise have been found in your lifetime”. Many patients are surprised and bewildered to discover that most breast cancers detected by screening would not have caused them problems if left untreated, there is no evidence that screening reduces overall mortality, and the evidence that screening reduces breast cancer deaths at all is controversial.’ He ends, ‘ …the breast screening establishment still seems determined to pressurise women to accept screening mammography rather than giving them the opportunity to decide for themselves if they feel that the benefits outweigh the risks. This may be good for those whose salaries are paid by the breast cancer screening industry, but I’m not convinced that it is right for my patients.’