Journal of the National Cancer Institute Advance Access originally published online on November 27, 2007
JNCI Journal of the National Cancer Institute 2007 99(23):1815; doi:10.1093/jnci/djm209
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
© The Author 2007. Published by Oxford University Press.
CORRESPONDENCE |
Re: Declines in Invasive Breast Cancer and Use of Postmenopausal Hormone Therapy in a Screening Mammography Population
Affiliations of authors: California Cancer Registry, Public Health Institute, Sacramento, CA (ASR); Northern California Cancer Center, Fremont, CA (CAC)
Correspondence to: Anthony S. Robbins, MD, PhD, California Cancer Registry, Public Health Institute, 1700 Tribute Road, Suite 100, Sacramento, CA 95815 (e-mail: arobbins{at}ccr.ca.gov).
The recent, sudden declines in breast cancer incidence in the United States (1,2) are unprecedented, and their origins are of great relevance to breast cancer prevention. To date, large population-based declines in breast cancer have been reported not only for the United States but also for Germany and New Zealand, although not for Norway, Sweden, and the Netherlands. Because hormone therapy (HT) use declined substantially in all of these areas after 2002, it has been suggested (3) that this variation in worldwide incidence trends weakens the conclusions of Kerlikowske et al. (2) and others that HT cessation was the major cause of the declines. We wish to note some relevant mathematical and biologic considerations.
First, consider a change in the prevalence (P), from P1 to P2, of a risk factor with relative risk = RR. The percent change in incidence (PCI) that would be expected is
 |
Suppose that the change in P is –65%. It should be noted that the same –65% change could represent a change from 13% to 5% (P1 = 0.13, P2 = 0.05) or from 38% to 13% (P1 = 0.38, P2 = 0.13). Let us also suppose that RR = 1.25. Under these conditions, PCI = –2% if P1 = 0.13, but PCI = –6% if P1 = 0.38. Clearly, it is not the percent change in P that drives changes in incidence but the absolute change in P. Regarding the impact of changing relative risk, let us assume that P changed from 38% to 13% but that in one scenario RR = 1.25 and in the other RR = 1.07. Here, PCI = –2% if RR = 1.07, but PCI = –6% if RR = 1.25. Again, it is clear that PCI is lower when the relative risk is lower.
In addition to duration of use, the relative risk associated with HT use may also depend on the specific HT formulation. These considerations of initial prevalence and relative risk may very well explain the very different changes in breast cancer incidence that have been observed in the United States, where the percent change in HT prevalence after 2002 was –66% (4), versus other countries that have also experienced substantial declines in HT use. For example, in the Netherlands the percent change in HT use from 2001 to 2005 was –42%, and yet there has been no perceptible change in age-adjusted breast cancer incidence (5). HT use in the Netherlands appears to have peaked at approximately 13%, versus approximately 38% in the United States (6). Dutch women appear to have used HT for short durations (<5 years), whereas long-term use was the norm in the United States. Epidemiologic data suggest that the risk for breast cancer with short-term hormone use is much lower (RR = 1.07) (7). For the Netherlands, the formula above would predict a PCI of close to zero, which agrees with the cancer surveillance data. Thus, these apparently counterfactual data from other countries with substantial declines in HT do not argue against the hypothesis that population-level changes in HT use in the United States and other countries may largely account for recent declines in breast cancer.
Funding
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.
NOTES
The ideas and opinions expressed herein are those of the authors and endorsement by the State of California, Department of Public Health, the National Cancer Institute, and the Centers for Disease Control and Prevention or their contractors and subcontractors is not intended nor should be inferred.
REFERENCES
(1) Ravdin PM, Cronin KA, Howlader N, Berg CD, Chlebowski RT, Feuer EJ, et al. The decrease in breast-cancer incidence in 2003 in the United States. N Engl J Med (2007) 356:1670–4.
(2) Kerlikowske K, Miglioretti DL, Buist DSM, Walker R, Carney PA. Declines in invasive breast cancer and use of postmenopausal hormone therapy in a screening mammography population. J Natl Cancer Inst (2007) (DOI: 10.1093/jnci/djm111).
(3) Zahl PH, Maehlen J. A decline in breast-cancer incidence. N Engl J Med (2007) 357:510–1.[Web of Science][Medline]
(4) Hersh AL, Stefanick ML, Stafford RS. National use of postmenopausal hormone therapy: annual trends and response to recent evidence. JAMA (2004) 291:47–53.
(5) Soerjomataram I, Louwman M, Visser O, van Leeuwen FE, Coebergh JW. Does the decrease in hormone-replacement therapy also affect breast cancer risk in the Netherlands? J Clin Oncol (2007) In press.
(6) van Duijnhoven FJ, van Gils CH, Bezemer ID, Peeters PH, van der Schouw YT, Grobbee DE. Use of hormones in the menopausal transition period in the Netherlands between 1993 and 1997. Maturitas (2006) 53:462–75.[CrossRef][Web of Science][Medline]
(7) Collaborative Group on Hormonal Factors in Breast Cancer. 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. Lancet (1997) 350:1047–59.[CrossRef][Web of Science][Medline]
Response to this Correspondence
CiteULike 
Connotea 
Del.icio.us What's this?
J Natl Cancer Inst 2007 99: 1816-1817.
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||