Forty‐year trends in menopausal hormone therapy use and breast cancer incidence among postmenopausal black and white women

After reports from the Women's Health Initiative randomized trial evaluating estrogen plus progestin, there was a sudden, substantial, and sustained decrease in all categories of menopausal hormone therapy, and the first reduction in age‐adjusted breast cancer incidence in more than 20 years was seen in 2003‐2004 among US women 50 years of age or older. Subsequent trends in breast cancer incidence have been described, but most reports have not focused on the postmenopausal age group or fully engaged the potential influence of reduced hormone therapy on breast cancer incidence trends by race/ethnicity. To address this gap, this commentary examines trends for annual age‐adjusted breast cancer incidence over a 40‐year period from 1975 to 2015 for white and black women on the basis of findings from the Surveillance, Epidemiology, and End Results 9 registries. Overall, the sharp decline in breast cancer incidence seen in 2003‐2004 was followed in the subsequent decade by a continued low breast cancer incidence plateau in white women that has largely persisted. In contrast, a new discordance between breast cancer incidence trends in black and white women has emerged. In the 2005‐2015 decade, a sustained increase in breast cancer incidence in black women has resulted in annual incidence rates comparable, for the first time, to those in white women. This commentary explores the hypothesis that the over‐decade‐long and discordant changes in breast cancer incidence rates in postmenopausal black and white women are, to a large extent, associated with changes in hormone therapy use in these 2 groups. The sharp decline in breast cancer incidence seen in 2003‐2004 has largely persisted, but in contrast, black women have experienced year‐to‐year increases in breast cancer. A hypothesis outlining the major contribution of the sustained reduction in menopausal hormone therapy to these findings is proposed.