A new Canadian study shows that a significant drop in breast cancer incidence among post-menopausal women from 2002 to 2004 coincided with a sharp drop in hormone replacement therapy (HRT) use during the same period. This is the first study to show the link between HRT use and breast cancer among Canadian women.
Many Canadian women stopped taking HRT in 2002 because the results from a large American clinical trial - the Women's Health Initiative - showed the risks of taking HRT outweighed the benefits.
These new findings add an important Canadian perspective to growing international evidence that HRT use is linked to increased breast cancer risk. The study is published online today in the Journal of the National Cancer Institute.
The Canadian Cancer Society research shows that from 2002 to 2004 the breast cancer incidence rate dropped by nearly 10 per cent among Canadian women aged 50-69. This coincided with a more than 50 per cent drop in the number of women in the same age group taking HRT between 2002 and 2004 (HRT use dropped from almost 13 per cent to five per cent).
This is the largest age group of HRT users in Canada.
During the same period, the rate of mammography use stayed the same for Canadian women. This suggests that the drop in breast cancer incidence was not due to fewer women getting mammograms. The only factor that changed substantially was HRT use.
"These findings give Canadian women meaningful information about breast cancer and how to reduce their risk of getting this disease," says Dr. Prithwish De, the study's lead investigator and an epidemiologist at the Canadian Cancer Society. "Breast cancer is the most common cancer among Canadian women, and we hope these findings will help lead the way to seeing fewer women diagnosed with this disease."
Currently, the Society recommends that women avoid taking HRT for any reason other than to relieve severe menopausal symptoms that have not responded to other treatment.
"These findings reaffirm the Society's position on the risks of HRT use and reinforce the importance of getting this message to Canadian women," says Heather Chappell, Director, Cancer Control Policy, Canadian Cancer Society. "As we approach Breast Cancer Awareness Month, this is one more piece of information we can give Canadian women to help them fight back against this disease."
Chappell urges women approaching menopause to talk to their doctors about the risks and benefits of taking HRT to determine the best course of action for them. "The severity of each woman's menopausal symptoms and her medical history should be considered. If a woman decides to take HRT, she should take the lowest effective dose for the shortest time possible."
The Canadian Cancer Society study
The research team estimated HRT use among Canadian women between 1996 and 2006 by examining data from the National Population Health Survey. This information was examined alongside national breast cancer incidence rates for the same time frame obtained from the Canadian Cancer Registry. The study focused primarily on combined HRT (estrogen plus progestin).
Additional findings from the research show:
- There was little change in breast cancer incidence rates in younger women (under age 50) and among older women (over the age of 70).
- The decline in the breast cancer incidence rate among women aged 50-69 years continued until 2005, after which time rates began to increase slightly.
- In 2002, nearly 30 per cent of Canadian women aged 50-69 were taking some form of hormone therapy. This dropped to 15 per cent in 2004.
"This study fills a gap in our knowledge about the link between HRT use and breast cancer risk for Canadian women," says De. "We anticipate that more research in this area will continue to shed light on this crucial health issue for Canadian women."
In addition to De, the members of the research team are:
- Dr C. Ineke Neutel, Department of Epidemiology and Community Medicine, University of Ottawa
- Dr Ivo Olivotto, Breast Cancer Outcomes Unit, BC Cancer Agency
- Dr Howard Morrison, Centre for Chronic Disease Prevention and Control, Public Health Agency of Canada.
October is Breast Cancer Awareness Month. The Canadian Cancer Society fights back against breast cancer by:
- supporting excellent breast cancer research
- educating women about early detection
- providing information and support to women living with breast cancer, their families and their caregivers
The Canadian Cancer Society fights cancer by doing everything we can to prevent cancer, save lives and support people living with cancer. Join the fight! Go to fightback.ca to find out how you can help. When you want to know more about cancer, visit our website at cancer.ca or call our toll-free bilingual Cancer Information Service at 1 888 939-3333.
For a copy of the research paper entitled Breast Cancer Incidence and Hormone Replacement Therapy in Canada please go to: http://jnci.oxfordjournals.org
Media Backgrounder
Drop in Breast Cancer Incidence among Canadian Women Linked to Decline in Hormone Replacement Therapy (HRT) Use
Today, the Canadian Cancer Society released research findings showing that a significant drop in breast cancer incidence among post-menopausal Canadian women coincided with a drop in hormone replacement therapy use.
The Society research shows that from 2002 to 2004 the breast cancer incidence rate dropped by nearly 10 per cent among Canadian women aged 50-69. This coincided with a more than 50 per cent drop in the number of women in the same age group taking HRT between 2002 and 2004 (HRT use dropped from almost 13 per cent to five per cent). This is the largest age group of HRT users in Canada.
General breast cancer statistics
- Breast cancer is the most common cancer among Canadian women.
- In 2010, it is estimated that 23,200 Canadian women will be diagnosed with breast cancer and about 5,300 will die from the disease.
- One in nine women is expected to develop breast cancer during her lifetime and one in 28 will die of it.
- The overall relative survival rate for breast cancer is 87 per cent.
- 80 per cent of breast cancer cases occur among women aged 50 and older; 52 per cent among women aged 50-69
Women's Health Initiative (WHI) study
A major American study called the Women's Health Initiative identified breast cancer risk associated with HRT use. More than 16,600 women were part of this large, well-designed study. The study was stopped in early 2002 primarily because HRT was found to increase the risk of breast cancer, but also because it appeared to increase the risk of heart disease, stroke and pulmonary embolism (blood clots in the lungs). The study concluded that the risks of hormone replacement therapy (estrogen plus progestin) outweighed the benefits.
Summary of current evidence about the link between HRT and breast cancer risk
- The risk of breast cancer increases the longer a woman takes HRT.
- The risk of breast cancer drops rapidly after a woman stops taking HRT.
- The risk of death from breast cancer is elevated in current users of HRT.
- HRT use is linked to recurrence of breast cancer in survivors.
- Mammography is less effective in women who use HRT because of increased breast density.
Information about menopause
- A woman's ovaries make two female hormones: estrogen and progesterone.
- With menopause, the ovaries stop producing these hormones. This can lead to symptoms such as hot flashes, night sweats, trouble sleeping, mood swings and vaginal dryness.
- Hormone therapy can be used to relieve these symptoms.
October is Breast Cancer Awareness Month. The Canadian Cancer Society fights back against breast cancer by:
- supporting excellent breast cancer research
- educating women about early detection
- providing information and support to women living with breast cancer, their families and their caregivers
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