Some of the strongest evidence linking hormone replacement therapy (HRT) to breast cancer risk came from a large study called the Women's Health Initiative (WHI). When WHI results were released in 2002, doctors and public health officials concluded:
- HRT use increases breast cancer risk
- HRT to manage menopausal symptoms should be used cautiously
After these results and conclusions were released, HRT use in the United States went down a lot. Over the next several years, the number of women diagnosed with breast cancer also went down. Hormone-receptor-positive breast cancer diagnoses dropped the most -- by 14.7%. Most doctors believe that the decrease in breast cancer diagnoses was directly related to the decrease in HRT use.
A study found a similar drop in HRT use and breast cancer diagnoses in Canadian women after the WHI results and conclusions were released.
Between 2002 and 2004, there was a nearly 10% decrease in the number of invasive breast cancer diagnoses in Canadian women between the ages of 50 and 69. Over the same period of time, HRT use among women in the same age group dropped more than 60%. In 2002, 12.7% of the women were using HRT; in 2004, only 4.9% of the women were using HRT.
The researchers also looked at HRT use and invasive breast cancer diagnoses from 1996 to 2000, BEFORE the WHI results were available:
- use of all forms of HRT increased about 1.7% each year
- combination HRT (contains both estrogen and progesterone) use increased about 4.9% each year; combination HRT has a stronger link to breast cancer than estrogen-only HRT
Invasive breast cancer diagnoses did drop slightly (0.9%) from 1996 to 2000; this drop was much smaller than the large drop (10%) in diagnoses between 2002 and 2004.
All these results support the idea that the large drop in breast cancer diagnoses in the 2 years after the WHI results were released was related to the drop in HRT use -- both in the United States and in Canada.
This study also found that invasive breast cancer diagnoses in Canada began to increase slightly in 2005. One possible explanation is that some HRT users who stopped using HRT in 2002 (or later) ALREADY had developed the beginnings of breast cancer. Because they stopped using HRT, the cancer grew more slowly than it would have if they'd continued to use HRT. Still, it did grow and was eventually diagnosed. So it seems HRT use also may affect breast cancer diagnosis numbers by encouraging the growth of breast cancer that has started to develop.
The side effects of menopause can dramatically reduce some women's quality of life. These women have to weigh the benefits of HRT use against the risks. If you're having severe hot flashes or other menopausal side effects and are considering taking HRT, talk to your doctor about:
- how to minimize your breast cancer risk -- research shows that taking combination HRT for fewer than 3 years doesn't significantly increase breast cancer risk
- the pros and cons of different types of HRT -- estrogen-only HRT appears to increase breast cancer risk less than combination HRT
- taking HRT for the shortest time possible
Together, you and your doctor can decide if HRT or another treatment to ease menopausal side effects might be right for you. If you decide to use HRT, try to make healthy lifestyle choices that can lower your breast cancer risk. During and after taking HRT, make sure to follow recommended breast cancer screening guidelines, including monthly breast self-exams, annual mammograms, and annual physical exams by your doctor.