The contribution of postmenopausal hormone use cessation to the declining incidence of breast cancer

Abstract

The striking decline in United States breast cancer incidence since 2002 has been widely attributed to a reduction in postmenopausal hormone use, yet very little analysis has been conducted to quantify the contribution of changes in hormone use to the declining trend. We used literature-based estimates of the relative risk and the changing prevalence of hormone use to estimate the impact of hormone use on the decline in breast cancer incidence between 2002 and 2003 among women aged 40-79. For the base case of a 44% decline in hormone use and a relative risk for current use of 1.5, we estimated that 43% of the decline in incidence was attributable to 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 hormone use is unlikely to account for more than half of the observed decline in breast cancer incidence between 2002 and 2003. Further efforts are needed to quantify the potential contributions of other factors, such as the plateau in screening mammography utilization.

Figure 1. Female breast cancer incidence, 1975–2007

Female breast cancer incidence in SEER 9 registries (all ages), invasive vs. in situ, 1975–2007 [21].

Figure 2. Comparing the observed decline in invasive breast cancer to that predicted by cessation of hormone use

Predicted age-specific breast cancer incidence in 2003 (dotted line), assuming a 44% decline in postmenopausal hormone use from 2002 and a relative risk of 1.5 associated with hormone use. The observed age-specific incidence in 2002 (solid line) and 2003 (dashed line) from the SEER 9 registries show that the predicted drop in incidence was less than that observed.

Figure 3. Percent of observed decline in incidence attributable to cessation of hormone use

This contour plot displays the percent of the observed decline in breast cancer incidence between 2002 and 2003 among women aged 40–79 years old that can be attributed to cessation of postmenopausal hormone use, depending on the relative risk associated with hormone use and the percent decline in hormone use experienced between 2002 and 2003.