Screening programmes should, as the UK national screening committee puts it, do more good than harm, and at a reasonable cost. Screening for breast cancer has become more controversial recently as some of the harms have been emphasised: here is a recent example.
It is very difficult to keep up with the enormous literature, so this summary is welcome. It comes from a committee set up in the UK to offer an 'independent' view. 'Independent' meant 'has never published on breast screening'. That tends to rule out everyone who knows anything about the subject, so the people selected for this high profile work were very great and very good in their own fields.
I think the key numbers to carry in your head are as follows:
20% reduction in mortality
1 death prevented per 235 women invited for screening
10% - 20% overdiagnosis.
Those are the numbers you need for conversations with your friends. but for written briefings you need much more precision: what do we mean by 'reduction in mortality', by 'deaths prevented' and by 'overdiagnosis' ? The paper sets all this out with great clarity.
Note also that this is for screening as delivered by the UK programme - three yearly, start at age 50, predominantly ethnic white population. Different parameters, different numbers!