Abstract A129: Declining incidence of breast cancer since 2002 in the United States: How much is explained by the decrease in postmenopausal hormone use?

Abstract

Abstract The striking decline in breast cancer incidence since 2002 in the United States has been widely attributed to discontinuation of postmenopausal hormone use following the results of the Women's Health Initiative (WHI) randomized trial. However, very little analysis has been conducted to quantify the contribution of cessation of hormone use to the observed decline in breast cancer incidence. We used literature-based estimates of the change in the prevalence of hormone use and the relative risk associated with hormone use to estimate the impact of cessation of hormone use on the observed decline in breast cancer incidence between 2002 and 2003 among women aged 40–79 years old. For the base case of a 46% decline in hormone use and a relative risk for current use of 1.5, we estimate that 42% of the decline in incidence was attributable to cessation of hormone use. By exploring a range of parameter values we found that high, unlikely values of the relative risk (i.e., ≥2.25) and/or the percent decline in hormone use (i.e., ≥75%) would be required to account for 100% of the observed decline in breast cancer incidence. We conclude that cessation of postmenopausal hormone use following the announcement of the results of the WHI is unlikely to account for more than half of the observed decline in breast cancer incidence among women aged 40–79 years old. The potential contributions of other factors should be examined in future studies, especially the role of the recent plateau in screening utilization. Citation Information: Cancer Prev Res 2010;3(1 Suppl):A129.