The burden of breast cancer is unremitting and we must do anything we can to contain it. It seems obvious that detecting tumours before they are clinically apparent is a good idea. But screening all women aged 50-70 every three years is but one way of containing the disease, and its appreciable financial costs need to be borne in mind (£75m (€90m; $110m) a year in the UK: £37.50 per woman invited and £45.50 per woman screened).

Screening for a progressive disease is justified only if earlier diagnosis and treatment improve disease progression. Since all healthy women aged 50-70 are called for breast screening, the benefits (reduced mortality) ought to be unambiguous and considerable and the risks of harm small. Since this is not always the case, national screening programmes rely primarily on faith, supported by large randomised studies. They are essentially based on their face validity and the apparent benefit among women with screen detected minute tumours. Scientific evidence plays too little a part, not least because it is much disputed.

The recent guidelines by the US Preventive Services Task Force on screening for breast cancer reviewed the evidence, most of which comes from eight large trials.1 The task force recommended changing current practice in the US to biannual mammography rather than annual screening and only for women aged 50-74, excluding those aged 40-49, provoking an almost hysterical response from screening enthusiasts.2 The recommendations were rejected.3

The US report pools results from all randomised studies and estimates that the mortality reductions attributable to breast screening are 15% for women aged 39-49, 14% …