Originally published as JCO Early Release 10.1200/JCO.2007.11.4132 on June 25 2007

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Regional Changes in Hormone Therapy Use and Breast Cancer Incidence in California From 2001 to 2004

Anthony S. Robbins, Christina A. Clarke

From the California Cancer Registry, Public Health Institute, Sacramento; Northern California Cancer Center, Fremont; and the Stanford University School of Medicine, Stanford, CA

Address reprint requests to Anthony S. Robbins, MD, PhD, California Cancer Registry, Public Health Institute, 1700 Tribute Rd, Suite 100, Sacramento, CA 95815; e-mail: arobbins{at}ccr.ca.gov

Purpose: Recently, an unprecedented 1-year 7% decrease in the overall incidence of invasive female breast cancer in the United States was reported. It has been suggested that the decrease resulted from the mass cessation of estrogen-progestin hormone therapy (EPHT) in 2002. We took advantage of California's unique population-based cancer surveillance resources to assess whether regional changes in breast cancer incidence observed between 2001 and 2004 correlated with regional changes in EPHT use between 2001 and 2003.

Methods: We obtained statewide cancer registry and California Health Interview Survey (CHIS) EPHT data for almost 3 million non-Hispanic white women age 45 to 74 years, residing in California's 58 counties. We examined trends in the age-adjusted incidence of invasive female breast cancer and compared these with trends in the use of EPHT, after grouping all California counties into three groups based on EPHT use in 2001. We also examined CHIS data on trends in screening mammography.

Results: In 2001, there were large regional differences in EPHT use and breast cancer incidence. From 2001 to 2004, incidence declined by 8.8% in the counties with the smallest EPHT reductions, by 13.9% in those with intermediate reductions, and by 22.6% in counties with the largest EPHT reductions. Between 2001 and 2003, CHIS data did not show any significant change in the proportion of women who reported having a mammogram in the previous 2 years.

Conclusion: These data support the hypothesis that changes in EPHT use in 2002 may be responsible for significant declines in breast cancer incidence between 2002 and 2003 and sustained through 2004.

Supported by the California Department of Health Services as part of the statewide cancer reporting program mandated by California Health and Safety Code Section 103885 (for collection of cancer incidence data); the National Cancer Institute's Surveillance, Epidemiology and End Results Program under Contract No. N01-PC-35136 awarded to the Northern California Cancer Center, Contract No. N01-PC-35139 awarded to the University of Southern California, and Contract No. N02-PC-15105 awarded to the Public Health Institute; and the Centers for Disease Control and Prevention's National Program of Cancer Registries, under Agreement No. U55/CCR921930-02 awarded to the Public Health Institute.

The ideas and opinions expressed herein are those of the authors and endorsement by the State of California, Department of Health Services, the National Cancer Institute, and the Centers for Disease Control and Prevention or their contractors and subcontractors is not intended nor should be inferred.

Authors' disclosures of potential conflicts of interest and author contributions are found at the end of this article.

published online ahead of print at www.jco.org on June 25, 2007.

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