Two Thirds of Breast Cancer Death Reductions are Due to Therapy Advances

Approximately one third of the reduction in breast cancer mortality (death) is due to screening, and the rest is presumably due to improvements in therapy. The research looked at different populations of women in Norway at different times. Norway rolled out its mammography program systematically over a 9 year period, creating groups that were and were not screened. In addition, they have good data on incidence-based mortality of breast cancer dating back to the 1980s. Incidence-based mortality (how many women per 100,000 die of breast cancer in a given year) is a much more valid measure of benefit than 5-year survival, which is heavily biased by over-diagnosis and over-treatment. To figure out how much of the reduction in breast cancer mortality is due to screening, the authors compared counties with and without screening during the years that it was implemented (1996-2005) and then compared women in these counties with women in the same counties 10 years earlier, when no one was being screened. Compared with the same counties 10 years earlier, they found that the rate of death was reduced by 7.2/100,000 in the screened counties and 4.8/100,000 in the unscreened counties. Thus, the difference in the reduction in mortality that can be attributed to screening alone was 2.4 deaths per 100,000 person-years, or one-third of the total reduction of 7.2 deaths. The rest of the reduction in mortality can presumably be attributed to improvements in treatment.