Why have breast cancer mortality rates declined?

- Breast cancer mortality in the USA has substantially declined from 1975 to 2010.
- There is no reduction in the incidence.
- Decline in mortality is unlikely due to prevention or to screening mammography.
- Improved survival is most noticeable for regional cancers, and is likely due to improved treatment.
- The large observed increase in the number of localized breast cancers suggests overdiagnosis.

The recent decline in breast cancer mortality in the USA might be due to prevention or to screening mammography or to improved treatment protocols. We sought to determine which factors are likely to be responsible for the observed decline in breast cancer mortality.We used the Surveillance, Epidemiology and End Results (SEER) database to estimate incidence rates, mortality rates, and survival from breast cancer for white women who were diagnosed with invasive breast cancer from 1975 to 2011.From 1975 to 2010, the mortality of breast cancer declined from 32 per 100,000 per year to 21 per 100,000 per year (34%). At the same time, the incidence increased by 30%, in particular for localized breast cancers (62%) without a commensurate decline in the number of regional breast cancers. From 1975 to 2002, 10-year survival increased by 28% (from 64.9% to 82.8%). The increase in survival was greater for regional cancers (23%), than for localized (10%) or for distant cancers (3%).The decline in breast cancer mortality in the USA from 1975 to 2010 is unlikely to be the result of advances in prevention or screening. The large increase in the incidence of localized cancers without a corresponding decrease in advanced breast cancers suggests a prominent stage shift, due to overdiagnosis. The drop in the mortality rate could be accounted for by an improvement in cancer survival, likely due to increased use of adjuvant chemotherapy over the period.