Breast screening saves lives

In my previous response, I pointed to the 16% mortality decline found
in three independent meta-analysis. This concerned all women, not those 50
and older. In those 50 and older the mortality decline was 22%.

However, I forgot to mention a fourth bias: breast cancer mortality
of the total population includes those at high risk, not eligible for
screening but for surveillance. In the Swedish meta-analysis, the breast
cancer mortality was substantially lower in the control population than in
the Swedish reference population. The estimate of 3 women saved per 1000
participants remains an optimistic extrapolation of 14 years of clinical
practice in dedicated trials to 25 year of everyday practice in the total
population.

In the USPSTF analysis (reference in previous response), the absolute
risk reduction of screening women over 50 was 1.2 per 1000 in 14 year.
Extrapolating this to 25 years, yields 2.1 per 1000, comfortably close to
the previous estimate of 3 (the difference being caused by the high prior
mortality in the age group 50 till 75).

Forward calculating from absolute risks, the estimate of lifes saved
by 20 years screening in 25 years of follow up is 2 in 1000 participating
women, or 2 weeks of gained life expectancy. Backward calculating from
population figures and relative risk reductions over the same period, the
estimate of saved lifes is 3 in 1000 participating women, or 3 weeks of
gained life expectancy.

Competing interests:
None declared