LAUSR

812 Cancer March 1, 2021 increasing incidence trends in women aged 20 to 29 years (1.6% per year) and 40 to 49 years (0.3% per year). It is interesting to note that, unlike the commentary by Chlebowski et al, these studies are based on analyses conducted using the Joinpoint Regression Program, which is widely used to quantify temporal trends in cancer rates. Although the authors correctly noted that the increase in the annual estimates of new breast cancer cases from 2005 to 2018 from the American Cancer Society largely reflects the growth and aging of the US population, these are model-based projections for which the methodology has changed over time and should not be used to track trends. It also is worth noting that the incidence rate per 100,000 White women aged ≥50 years was higher in 2015 (367.61) than in 2003 (361.22). Finally, Chlebowski et al concluded that changes in hormone therapy use among postmenopausal women could provide a plausible explanation for much of the sustained lower breast cancer incidence noted among White women since 2003, as well as contribute to the discordant findings observed among Black women. Although it is likely true that the sharp drop in incidence rates between 1999 and 2004 that was largely confined to White women aged ≥50 years with hormone receptor–positive (HR+) breast cancer was driven primarily by the decreased use of MHT, given that the increased risk of breast cancer associated with MHT appears to be limited to HR+ subtypes, the small decline in mammography screening prevalence from 70% in 2000 to 64% in 2015 also may have contributed. Moreover, the longer-term effects of the sustained lower use of menopausal hormones are less clear given the slow increase in the majority of women (younger, older, Black, and White) that has been shown to be confined to patients with HR+ disease, with concomitant declines observed for patients with hormone receptor–negative breast cancers. Other factors such as trends in obesity, as the authors suggest, as well as trends in reproductive factors, including a later age at first birth and having fewer children, may be influencing these disparate trends.