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Breast cancer incidence and hormone replacement therapy in Canada
Prithwish De1, C Ineke Neutel, Ivo Olivotto
1MHSc, Cancer Control Policy, Canadian Cancer Society, 10 Alcorn Ave, Ste 200, Toronto, ON, Canada M4V 3B1. pde@cancer.ca
Background:
In 2002, results of the Women's Health Initiative clinical trial indicated that the long-term risks of combined estrogen and progestin hormone replacement therapy outweighed the health benefits for postmenopausal women. The resulting decline in use of hormone replacement therapy was followed by concurrent decreases in breast cancer incidence in several countries. The aim of the current study was to determine whether similar declines occurred in Canada.
Methods:
Data on prescriptions for hormone therapy were obtained from a national registry of pharmacy-filled prescriptions to confirm the reported trend in use of hormone replacement therapy among approximately 1200 women aged 50-69 years who participated in the National Population Health Survey between 1996 and 2006 and whose data were extrapolated to the Canadian female population. Age-standardized incidence rates for breast cancer were obtained from the population-based Canadian Cancer Registry for the same period, and mammography rates were obtained from the Canadian Community Health Survey. Joinpoint regression was used to examine changes in trends in the use of hormone replacement therapy and breast cancer incidence.
Results:
A reduced frequency of use of hormone replacement therapy was reflected in the decrease in dispensed hormone therapy prescriptions after 2002. The largest drop in use of combined hormone replacement therapy (from 12.7%, 95% confidence interval [CI] = 10.1% to 14.2%, to 4.9%, 95% CI = 3.4% to 6.8%, of all women) occurred between January 1, 2002, and December 31, 2004, among women aged 50-69 years. This drop occurred concurrently with a 9.6% decline in the incidence rate of breast cancer (from 296.3 per 100,000 women, 95% CI = 290.8 to 300.5 per 100,000 women, in 2002 to 268.0 per 100,000 women, 95% CI = 263.3 to 273.5 per 100,000 women, in 2004). Mammography rates were stable at 72% over the same period.
Conclusion:
During the period 2002-2004, there was a link between the declines in the use of hormone replacement therapy and breast cancer incidence among Canadian women aged 50-69 years, in the absence of any change in mammography rates.
Insights
Following the 2002 Women's Health Initiative trial, Canadian women aged 50-69 saw a significant drop in hormone replacement therapy use. This decline coincided with a decrease in breast cancer incidence, indicating a potential link.
Area of Science:
- Oncology
- Epidemiology
- Public Health
Background:
- The Women's Health Initiative trial (2002) revealed risks of combined hormone replacement therapy (HRT) outweighing benefits for postmenopausal women.
- A subsequent global decline in HRT use was observed, with potential impacts on breast cancer rates.
- This study investigated whether similar trends in HRT use and breast cancer incidence occurred in Canada.
Purpose of the Study:
- To determine the trends in hormone replacement therapy (HRT) use among Canadian women aged 50-69 years between 1996 and 2006.
- To assess changes in breast cancer incidence rates in the same demographic during the study period.
- To evaluate the correlation between HRT use and breast cancer incidence in Canada post-2002.
Main Methods:
- Prescription data from a national registry tracked HRT use in women aged 50-69.
- Breast cancer incidence rates were obtained from the Canadian Cancer Registry.
- Mammography rates were sourced from the Canadian Community Health Survey.
- Joinpoint regression analysis examined trend changes in HRT use and breast cancer incidence.
Main Results:
- A significant decrease in HRT prescriptions was observed after 2002, with combined HRT use dropping from 12.7% to 4.9% among women aged 50-69 by 2004.
- Concurrently, breast cancer incidence rates declined by 9.6% between 2002 and 2004.
- Mammography screening rates remained stable at 72% during this period.
Conclusions:
- A notable association was found between reduced hormone replacement therapy use and decreased breast cancer incidence in Canadian women aged 50-69 years from 2002 to 2004.
- This link was observed despite stable mammography screening rates.
- The findings suggest a potential impact of HRT reduction on breast cancer trends in the Canadian population.
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