Hormone therapy and the rise and perhaps fall of US breast cancer incidence rates: critical reflections.

BACKGROUND: Results of the Women's Health Initiative (WHI) study-which to many unexpectedly showed that hormone therapy (HT) did not decrease and may in fact have elevated risk of cardiovascular disease, while also finding expected links between HT and breast cancer-have spurred critical reflection chiefly regarding the cardiovascular results. Suggesting similar scrutiny of cancer epidemiology is warranted are new studies linking the post-WHI drop in HT use to a substantial decline in breast cancer incidence and the implications of these findings for prior explanations of the rising rates of US breast cancer incidence during the 1980s.
METHODS: Literature search for review and research articles on temporal trends in US breast cancer incidence during the past 25 years, starting in the mid-1980s, when extant epidemiologic evidence had already indicated that HT increased risk of breast cancer.
RESULTS: Among the 21 articles identified, spanning from 1987 to 2007, nine included no mention of HT as a possible factor contributing to the steep rise in breast cancer incidence in the 1980s, seven included a minor mention and only five (one published in 2003, the others in 2006 and 2007) provided any substantive discussion of this issue-but only in relation to current trends and not the 1980 rise in breast cancer incidence.
CONCLUSION: A critical appraisal of the epidemiologic literature highlights important gaps in explanations for breast cancer incidence trends and also how current and changing population patterns of disease distribution are ultimately what put our aetiologic explanations to the test.