Cancer. 2020 Mar 25. doi: 10.1002/cncr.32846. [Epub ahead of print]
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.
COMMENTARY LIMITATIONS AND FUTURE DIRECTIONS
The major focus of the current commentary is the effects of the WHI hormone therapy trial reports on secular hormone therapy use in postmenopausal women and resulting time trend changes in total invasive breast cancer incidence. As a result, our commentary does not address the issue of time trends in breast cancer subtypes, perhaps most importantly estrogen receptor (ER)–negative breast cancers. We briefly outline current findings in this area and identify areas needing ongoing investigation. According to SEER data findings, divergent ERspecific breast cancer time trends have been seen with a steady decrease of nearly 2% per year in ER-negative incidence rates since 1992,66 with trends not substantially influenced by the reduction in hormone therapy use.
Although it is known that risk factor associations differ by ER subtype,68 the basis for the ongoing reduction in ERnegative cancer has not been established. Because poorprognosis, triple-negative (ER-negative, PR-negative, HER2-negative) breast cancers are more commonly diagnosed in black women,47,48 time trends in breast cancer subtypes have implications for potential changes in the known black/white disparity regarding breast cancer outcomes. Although most recent findings have identified a relatively stable breast cancer risk in white women with increasing breast cancer risk in black women, modeling that incorporates Hispanic and non-Hispanic status projects breast cancer rates slowly increasing for non- Hispanic white women and slowly decreasing for non- Hispanic black women.69 Ongoing vigilance is needed to further define these potentially important relationships.
In conclusion, changes in hormone therapy use in postmenopausal women provide a plausible explanation for a substantial component of the sustained lower breast cancer incidence seen in white women since 2003 and contribute to the discordant findings among black women, for whom, in contrast, increases in breast cancer incidence rates were seen over the 2005-2015 decade.