A trial to study the effect on breast cancer mortality of annual mammographic screening in women starting at age 40

Objective-Although there is clear evidence from randomised trials of the ef fectiveness of mammographic screening in women over 50 in reducing mortalit y from breast cancer, the benefit of screening in younger women remains les s certain. This paper describes a randomised controlled trial in progress t o study the effect on breast cancer mortality of annual mammographic screen ing of of women starting at age 40-41. Setting-Screening centres of the NHS Breast Screening Programme, Methods-In 1991 a national multicentre randomised controlled trial was set up by the United Kingdom Coordinating Committee on Cancer Research (UKCCCR) . This trial (the "age" trial) aims at recruiting 195 000 women aged 40-41 such that 65 000 form a study group and the remaining 130 000 a control gro up. Women in the study group are invited for annual screening by mammograph y, and become eligible for the National Health Service Breast Screening Pro gramme (NHSBSP) after age 50. Those in the control group are not offered an y additional services, but will also join the national programme after age 50. All malignant breast histology in trial women is recorded. Analysis-The principal method of evaluation will be the comparison of cumul ative breast cancer mortality rates in the study and control groups; interi m analyses of prognostic factors of breast cancers will also be possible. A dditional NHS screening costs incurred owing to lowering the age of screeni ng will be assessed as part of an economic evaluation. The amount of unsche duled screening occurring in the control group of the trial will also be as sessed.