Screening and its effect on breast cancer mortality rates
- RG Blanks1
© Current Science Ltd 2000
Published: 1 October 2000
In the Health of the Nation document published by the Department of Health in 1993 it was stated that the eventual success of the breast screening programme would be measured in terms of the breast cancer mortality reduction achieved. Unfortunately, outside the environment of randomised controlled trials the actual mortality reduction from screening is extremely difficult to measure with any precision. This is because national mortality statistics between the start of screening in 1988 and the present day have been affected not only by screening, but also by treatment improvements, cohort effects, earlier presentation outside the screening programme and even changes in the way breast cancer deaths are coded.
Additionally, the full effect of screening in national statistics is not likely to be achieved until 2005-2010 rather than the year 2000, as often reported. This is because of two major factors. Firstly, many deaths from breast cancer in the 1990s will be from women who were diagnosed with breast cancer before invitation to screening (full coverage was not achieved until 1995). Secondly, the screening sensitivity of the NHSBSP did not achieve parity with the Swedish-Two County study until 1996/97. In the early years of screening there was a major shortfall of invasive cancers, which led to high interval cancer rates and a projected mortality reduction much less than 25%. The combination of these two factors will lead to a considerably lower mortality reduction than 25% by the year 2000. Nevertheless some mortality reduction from screening would be expected and standard epidemiological techniques (age-cohort modelling) have been employed in an attempt to measure this.