Why is breast-cancer mortality declining?

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. In this review, we argue that although some of the decline in breast-cancer mortality is due to a reduction in breast-cancer risk, most of it can probably be attributed to adjuvant systemic therapy and the earlier detection of palpable tumours. We also explain why advances in the treatment of breast cancer might be outpacing the value of mammography screening. Since age-adjusted mortality rates are the most basic measure of progress in the treatment of breast cancer, we suggest that careful scrutiny of recent trends in breast-cancer mortality may provide important insights into the effectiveness of novel strategies for diagnosis and treatment.