A breast cancer clinical trial that assigned patients to two or five years of adjuvant tamoxifen therapy found that five years of tamoxifen reduced the risk of death from coronary heart disease. Risk of death from breast cancer or from all causes combined was also reduced with five-years of tamoxifen, as was the risk of developing contralateral breast cancer. Five years of tamoxifen, however, increased the risk of endometrial cancer. The study was published in the Journal of the National Cancer Institute.
Tamoxifen acts as an anti-estrogen. Because many breast cancers are stimulated to grow by estrogen, treatment with tamoxifen can slow or stop cancer growth. Adjuvant therapy with tamoxifen can help prevent recurrent or contralateral breast cancer.
To compare survival after two or five years of adjuvant tamoxifen therapy, researchers in Sweden conducted a randomized clinical trial among 4610 postmenopausal women with early-stage breast cancer. All women were under the age of 75.
After roughly 10 years of follow-up, the researchers report that survival was better among the women who received five years of tamoxifen than among those who received two years of tamoxifen. The analysis included only the 4175 patients who were recurrence-free after two years.
Women who received five years of tamoxifen had a reduced risk of:
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- Death from any cause
- Death from breast cancer
- Development of contralateral breast cancer
- Death from coronary heart disease
There were 78 deaths from coronary heart disease among the 2129 women who received two years of tamoxifen, whereas there were 24 fewer (54) deaths among the 2046 women who received five years of tamoxifen. The reduction in risk of coronary heart disease appears to be a late benefit; the benefit did not become apparent until roughly seven years after diagnosis. Up until that point, the two study groups had similar rates of coronary heart disease.
Women who received five years of tamoxifen did have an increased risk of developing endometrial cancer, though there were few deaths due to endometrial cancer: Among women who received five years of tamoxifen, there were 41 cases of endometrial cancer and 7 endometrial cancer deaths; among women who received two years of tamoxifen, there were 24 cases of endometrial cancer and 6 endometrial cancer deaths.
The researchers conclude that their results “strongly support the use of tamoxifen in the adjuvant treatment of breast cancer patients.”
Reference: Nordenskjöld B, Rosell J, Rutqvist L-E et al. Coronary Heart Disease Mortality After 5 Years of Adjuvant Tamoxifen Therapy: Results from a Randomized Trial. *Journal of the National Cancer Institute.*2005;97:1609-1610.
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