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Recent Declines in Hormone Therapy Utilization and Breast Cancer Incidence: Clinical and Population-Based Evidence

Surveillance Research, Northern California Cancer Center, Fremont CA, and Department of Health Research and Policy, Stanford University School of Medicine, Stanford, CA

Connie S. Uratsu, Joseph V. Selby, Larry H. Kushi, Lisa J. Herrinton

Division of Research, Kaiser Permanente, Oakland CA

To the Editor:

Long-term use of estrogen- or progestin-containing hormone therapies (HT) is well recognized to be associated with increased risk of breast cancer both in observational studies and the Women's Health Initiative (WHI) randomized trial.¹ After the early termination of the trial in July 2002 and the subsequent media coverage, reports from clinical series indicated immediate declines of 28% to 46% in prevalences of HT and estrogen-only (ET) use.^2,3 The population-level impact of these declines on breast cancer are uncertain given the 2- to 3-year lag time between diagnosis and data availability in cancer registries.

To better understand the possible impact from changes in HT on breast cancer in larger populations, we compared recent secular trends in HT use and breast cancer incidence in available clinical and population-based data resources, including recently released cancer registry data for the year 2004. We calculated the annual prevalence of HT use and the annual incidence of invasive breast cancer for the period from 1994 to 2003 for women ages 50 to 74 years in Kaiser Permanente's (Oakland, CA) Northern California region (KPNC), a large integrated health-delivery system from which computerized pharmacy, membership, and hospital cancer registry data were obtained. Women filling at least two prescriptions (generally constituting 90 days per prescription) of HT or ET in any calendar year were considered users for that year. First primary invasive breast cancer (International Classification of Disease–Oncology, 3rd edition [ICD-O-3]⁴ site 50.0-50.9) diagnoses were identified, with histologic subtypes defined as ductal (ICD-O-3 codes 8500), or "with lobular component" (ICD-O-3 codes 8520, 8522, 8524). Yearly denominators included women who were KPNC members for at least 11 months of the year, and excluded those with unknown age or county of residence. Population-based breast cancer incidence rates for the 13-county catchment area for KPNC and for the state of California were obtained from the California Cancer Registry for the same ICD-O-3 specifications and age group, but for the time period including 2004, which was the most recent year for which data were available. All rates were age-adjusted to the 2000 US standard.

Figure 1 illustrates that between 2001 and 2003, the calendar years before and after the WHI announcement, age-adjusted rates of HT and ET use in KPNC members declined 68% and 36%, respectively. For the same time period, breast cancer incidence declined 10% in KPNC members, 11% in the catchment population, and 11% in the state. For 2004, breast cancer incidence rates in the catchment population and the state were lower than the rates for 2003. Comparable patterns of decline were observed for both the ductal and lobular histologic subtypes (data not shown).

View larger version (14K): [in this window] [in a new window] [PowerPoint Slide for Teaching]   Fig 1. Yearly rates of prevalence of estrogen-only and estrogen/progestin–containing hormone therapy use and incidence of invasive first primary breast cancer in Kaiser Permanente–Northern California (KPNC) members, the 13-county KPNC catchment area, and the state of California, from 1994 to 2004.

Authors' Disclosures of Potential Conflicts of Interest

Although all authors completed the disclosure declaration, the following author or immediate family members indicated a financial interest. No conflict exists for drugs or devices used in a study if they are not being evaluated as part of the investigation. For a detailed description of the disclosure categories, or for more information about ASCO's conflict of interest policy, please refer to the Author Disclosure Declaration and the Disclosures of Potential Conflicts of Interest section in Information for Contributors.

Authors Employment Leadership Consultant Stock Honoraria Research Funds Testimony Other Christina A. Clarke Williams Love O'Leary Craine & Powers, PC

ACKNOWLEDGMENTS

This study was supported by the SEER Rapid Response Surveillance Study program by a supplement to contract N01-CN-35136 with the National Cancer Institute. The collection of cancer incidence data used in this study was 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; the National Cancer Institute's Surveillance, Epidemiology and End Results Program under contract N01-PC-35136 awarded to the Northern California Cancer Center, contract N01-PC-35139 awarded to the University of Southern California, and contract 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.

REFERENCES

1. Writing Group for the Women's Health Initiative Investigators: Risks and benefits of estrogen plus progestin in healthy postmenopausal women: Principal results from the Women's Health Initiative randomized controlled trial. JAMA 288 : 321 -333, 2002[Abstract/Free Full Text]

2. Buist DS, Newton KM, Miglioretti DL, et al: Hormone therapy prescribing patterns in the United States. Obstet Gynecol 104 : 1042 -1050, 2004[Abstract/Free Full Text]

3. Wei F, Miglioretti DL, Connelly MT, et al: Changes in women's use of hormones after the Women's Health Initiative estrogen and progestin trial by race, education, and income. J Natl Cancer Inst Monogr 106 -112, (No. 35)

4. Fritz A, Percy C, Jack A, et al: International Classification of Diseases for Oncology (ed 3). Geneva, Switzerland, World Health Organization, 2000

5. Breast cancer and hormone replacement therapy: Collaborative reanalysis of data from 51 epidemiological studies of 52,705 women with breast cancer and 108,411 women without breast cancer: Collaborative Group on Hormonal Factors in Breast Cancer. Lancet 350 : 1047 -1059, 1997[CrossRef][Medline]

6. Dietel M, Lewis MA, Shapiro S: Hormone replacement therapy: Pathobiological aspects of hormone-sensitive cancers in women relevant to epidemiological studies on HRT—A mini-review. Hum Reprod 20 : 2052 -2060, 2005[Abstract/Free Full Text]

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