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 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.
Population statistics indicate that age-adjusted breast-cancer mortality rates began to decline during the early 1990s in many developed countries. For several decades before 1990, breast-cancer mortality rates in these countries had been either stable or increasing. Many investigators attribute the decline in mortality to mammography screening. However, randomised prospective trials indicate that there is a delay of 10 years before the effect of such screening can be seen in mortality statistics. In many developed countries, screening programmes were launched in the late 1980s and early 1990s, so the sudden decline in breast-cancer mortality in the early 1990s was much too soon to be attributable to mammography screening.