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In Reply

Northern California Cancer Center, Fremont, CA

Anthony S. Robbins

California Cancer Registry, Public Health Institute, Sacramento, CA

Soerjomataram and colleagues point out the wide range in prevalence of hormone therapy (HT) use across Europe during the 1990s, from the Netherlands, where HT use was one-third that in the US, to Germany,¹ where it was comparable to the United States. They also nicely summarize the mathematical considerations underlying HT-related changes in breast cancer incidence. They correctly point out that only small decreases in breast cancer incidence would be expected after HT declines if (1) the absolute prevalence of HT use was low to begin with; or (2) most of the HT use was short term. In the Netherlands, both of these conditions applied; in California, neither did. Furthermore, HT-associated relative risks may depend on formulation; in North America, women more commonly use conjugated equine estrogen and medroxyprogesterone acetate, while in Europe, common HT preparations include estradiol and other progestins (eg, micronized progesterone).

Thus, the absence of a perceptible drop in breast cancer in the Netherlands after 2001 is not surprising and is entirely consistent with our data from California,² and with other recent data documenting strong correlations between population-level HT use and breast cancer incidence in well-screened populations in the United States.^3,4 Besides the report from Germany,¹ other reports have recently been published describing breast cancer incidence trends in Geneva, Switzerland,⁵ Canada,⁶ Norway,⁷ Sweden,⁸ and New Zealand.⁹ In interpreting these data, we concur with our Dutch colleagues that large declines in the incidence of breast cancer are not always expected after substantial declines in the prevalence of HT use. We also second their call for continued close monitoring of international data in coming years, which will help us to more fully understand the HT/breast cancer relationship, in light of the worldwide "natural experiment" that occurred after the early termination of the estrogen/progestin arm of the Women's Health Initiative.

AUTHORS' DISCLOSURES OF POTENTIAL CONFLICTS OF INTEREST

Employment or Leadership Position: None Consultant or Advisory Role: None Stock Ownership: None Honoraria: None Research Funding: Christina A. Clarke, Northern California Cancer Center; Anthony S. Robbins, California Cancer Registry, Public Health Institute Expert Testimony: Christina A. Clarke, Williams Love O'Leary Craine & Powers, PC (C) Other Remuneration: None

ACKNOWLEDGMENTS

The collection of cancer incidence data used in this study was supported by the California Department of Public Health 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 U55/CCR921930-02 awarded to the Public Health Institute.

REFERENCES

1. 1. Katalinic A, Rawal R: Decline in breast cancer incidence after decrease in utilisation of hormone replacement therapy. Breast Cancer Res Treat doi:10.1007/s10549-007-9566-z, 2007

2. Robbins AS, Clarke CA: Regional changes in hormone therapy use and breast cancer incidence in California from 2001 to 2004. J Clin Oncol 25 : 3437 -3439, 2007[Abstract/Free Full Text]

3. Clarke CA, Glaser SL, Uratsu CS, et al: Recent declines in hormone therapy utilization and breast cancer incidence: Clinical and population-based evidence. J Clin Oncol 24 : e49 -e50, 2006[Free Full Text]

4. Glass AG, Lacey JV, Carreon D, et al: Breast cancer incidence, 1980-2006: Combined roles of menopausal hormone therapy, screening mammography, and estrogen receptor status. J Natl Cancer Inst 99 : 1152 -1161, 2007[Abstract/Free Full Text]

5. Verkooijen HM, Koot VCM, Fioretta G, et al: Hormone replacement therapy, mammography screening and changing age-specific incidence rates of breast cancer: An ecological study comparing two European populations. Breast Cancer Res Treat doi:10.1007/s10549-007-9554-3, 2007 .

6. Kliewer EV, Demers AA, Nugent ZJ: A decline in breast-cancer incidence. N Engl J Med 357 : 509 -510, 2007[Free Full Text]

7. Cancer in Norway 2005. Oslo: Cancer Registry of Norway (Kreftregisteret), 2006

8. Cancer Incidence in Sweden 2005. Stockholm: National Board of Health and Welfare (Socialstyrelsen), 2007

9. Johnston M: Breast cancer drop linked to fall in use of HRT. New Zealand Herald. http://www.nzherald.co.nz/section/story.cfm?c_id=204&objectid=10416198. December 20, 2006

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