Breast cancer incidence, 1980-2006: combined roles of menopausal hormone therapy, screening mammography, and estrogen receptor status.

BACKGROUND: Breast cancer incidence has been rising since at least 1935-1939, but recent US data reveal a statistically significant decline in breast cancer incidence in 2003 that persisted through 2004. Identifying the specific contributions of the potential causes of this long-term increase and the recent decrease in incidence has been challenging. Marked changes in rates of mammography screening and use of menopausal hormone therapy since 1980 have added further complexity. We examined the potential association between menopausal hormone therapy use and recent changes in breast cancer incidence.

METHODS: Using tumor registry, clinical, pathology, and pharmacy data from Kaiser Permanente Northwest, a large prepaid US health plan, we compared age-specific and age-adjusted breast cancer incidence rates (2-year moving averages) with use of screening mammography and dispensed menopausal hormone therapy prescriptions between 1980 and 2006. Temporal changes in incidence rates were assessed via joinpoint regression.

RESULTS: A total of 7386 incident invasive breast cancers were diagnosed in plan members from 1980 through 2006. Overall age-adjusted breast cancer incidence rates per 100,000 women rose 25% from the early 1980s (105.6) to 1992-1993 (131.7) and an additional 15% through 2000-2001 (151.3), then dropped by 18% to 2003-2004 (123.6) and edged up slightly in 2005-2006 (126.2). These patterns were largely restricted to women aged 45 years or older and to estrogen receptor-positive (ER+) breast cancers. Incidence rates of ER-negative tumors experienced neither of the rises seen for ER+ tumors but also fell precipitously from 2003 through 2006. Rates of mammography screening sharply increased from 1980 to 1993 but then leveled off, and 75%-79% of women aged 45 years or older received a mammogram at least once every 2 years from 1993 through 2006. Menopausal hormone therapy dispensings, particularly of estrogen-plus-progestin formulations, increased from 1988 to 2002 but then dropped by approximately 75% after 2002.

CONCLUSIONS: From 1980 through 2006, quantitative and qualitative trends in breast cancer incidence rates, particularly for ER+ tumors, parallel major changes in patterns of mammography screening and use of menopausal hormone therapy.