Mammographic screening and mammographic patterns

The main interest in mammography has focused on its value as a method of screening. However, the population-screening trials conducted over the past 35 years have generated extensive longitudinal data on the relation of mammographic features both to tumour behaviour and the future risk of breast cancer in the normal population. In this review we briefly examine the effectiveness of mammographic screening, then discuss more generally the contribution that mammography can make to understanding the natural history and epidemiology of breast cancer.Mammography as a method of screening for the early detection of breast cancer has undergone many randomised trials. The results of seven of the eight trials that have been published display a considerable consistency. For women over 50 years of age at entry to a trial, the reduction in breast cancer mortality in those invited to screening is approx. 25%, and in women who are screened the reduction is approx.33% [1]. For women under the age of 50 (the lower age limit varies across the trials between 35 and 40 years), the reduction in breast cancer mortality is considerably less, approx. 15% in all women invited to screening [2]. The one discrepant trial is the Canadian National Breast Screening. Two aspects of this trial give cause for concern. Firstly, an independent review of the quality of the mammography concluded that, at least in the early stages, the quality was unacceptably poor [3]. No one has ever suggested that poor mammography is effective. Secondly, there was a substantial and unexplained excess of advanced cancers at randomisation among women randomised to mammography, giving rise to concern that the randomisation process might have been poorly controlled [4,5].In view of the importance of breast screening to public health, and the soundness of the evidence demonstrating benefit, it was unfortunate that The Lancet chose to publish an incompetent attempt at an overview [6]. The shortcomings of that paper are well