Abstract
IntroductionRecent, international declines in breast cancer incidence are unprecedented, and the causes remain controversial. Few data sources can address breast cancer incidence trends according to pertinent characteristics like hormone therapy use history.MethodsWe used the prospective California Teachers Study to evaluate changes in self-reported use of menopausal hormone therapy (HT) between 1995 to 1996 and 2005 to 2006 and age-adjusted breast cancer incidence among 74,647 participants aged 50 years or older. Breast cancer occurrence was determined by linkage with the California Cancer Registry.ResultsDuring 517,286 woman years of follow up, 565 in situ and 2,668 invasive breast cancers were diagnosed. In situ breast cancer incidence rates in this population did not change significantly from 2000 to 2002 to 2003 to 2005, whereas rates of invasive breast cancer declined significantly by 26.0% from 528.0 (95% confidence intervals (CI) = 491.1, 564.9) per 100,000 women in 2000 to 2002 to 390.6 (95% CI = 355.6, 425.7) in 2003 to 2005. The decline in invasive breast cancer incidence rates was restricted to estrogen receptor-positive tumors. In 1996 to 1999 and 2000 to 2002 invasive breast cancer incidence was higher for women who reported current HT use especially estrogen-progestin (EP) use at baseline than for never or past users; but by 2003 to 2005 rates were comparable between these groups. For women who were taking EP in 2001 to 2002,75% of whom had stopped use by 2005 to 2006, incidence had declined 30.6% by 2003 to 2005 (P = 0.001); whereas incidence did not change significantly for those who never took HT (P = 0.33).ConclusionsFew data resources can examine prospectively individual HT use and breast cancer diagnosis. Stable in situ breast cancer rates imply consistent levels of screening and suggest recent declines in invasive breast cancer to be explained predominantly by changes in HT use.
Highlights
Recent, international declines in breast cancer incidence are unprecedented, and the causes remain controversial
A sharp decrease in breast cancer incidence in 2002 was reported by at least one cohort defined by regular mammography use [4], but far, data documenting incidence trends among women according to their personal hormone therapy (HT) use are very limited
Capitalizing on the capacity to examine long-term trends according to personal HT use history in the California Teachers Study (CTS), we evaluated changes in breast cancer occurrence over the period from 1996-2005
Summary
International declines in breast cancer incidence are unprecedented, and the causes remain controversial. Few data sources can address breast cancer incidence trends according to pertinent characteristics like hormone therapy use history. Others have argued that changes in mammography use are more likely to be responsible, because subtle declines in breast cancer incidence began in 1999, predating publication of the Women’s Health Initiative trial results, and because of the uncertain biological plausibility of an instantaneous change in risk after HT cessation [5]. A sharp decrease in breast cancer incidence in 2002 was reported by at least one cohort defined by regular mammography use [4], but far, data documenting incidence trends among women according to their personal HT use are very limited. Capitalizing on the capacity to examine long-term trends according to personal HT use history in the CTS, we evaluated changes in breast cancer occurrence over the period from 1996-2005
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