There were 2082 cases of breast cancer identified during the 1980 through 1 995 follow-up period.
After adjusting for age, education, body mass index, history of mammography and age at menopause, compared with women who had not taken
HRT, the authors published their study at the Journal of American Medical Association, showing the following results:
- The investigators found that the risk of breast cancer increased the longer women took hormone replacement therapy.
- Compared with women who did not take hormone replacement therapy, those who took estrogen-progestin recently (during the last 4 years) had a 40% higher risk of breast cancer.
- For those who had recently taken estrogen alone, the risk of breast cancer increased by 1% for each year of use.
- The risk per year was significantly higher for recent users of estrogen and progestin combined: 8% for each year of use.
This means a woman taking only estrogen for 20 years would have a 20 percent increased risk of breast cancer, yet a woman taking the combination therapy for 20 years would have a 160 percent increased risk of breast cancer.
"These results, as well as those from other studies, suggest that women who take hormones for two to three years for relief of menopausal symptoms are at increased risk of breast cancer," said Catherine Schairer, Ph.D. But the difference between the two types of hormone therapy was only statistically significant in leaner women, not those who were overweight or obese. In her comments to Reuters Health, Schairer said that there were not enough heavier women in the study who had taken combination therapy to get accurate results.
More studies evaluating longer-term use of estrogen in combination with progestin and different combination regimens of hormones are needed in the future. However, decisions for women and their physicians should be made based on the individual considerations.
Regardless of hormone use, Schairer said, "It's very important for all women to get periodic (breast cancer) screening. Women on hormone replacement therapy should be particularly careful."