Cancer screening studies showing reduced cancer-specific mortality may not be powered for all-cause mortality.

“what you fail to appreciate is those studies are never powered for all cause mortality and if you reduce breast cancer mortality by 40% or 30% that translates to a trivial reduction in all cause mortality because breast cancer is still just one of 50 Cancers and even though it's a relatively prevalent cancer over the period of time of a study which is typically 5 to S years the actual number of women who were going to die of breast cancer is still relatively small compared to the number of women period who were going to die of anything”