TUESDAY, Feb. 17 (HealthDay News) -- A large study of tibolone, a drug used to treat menopausal symptoms and to prevent osteoporosis, was halted early after researchers found that the synthetic steroid significantly increased the risk of recurrent breast cancer among survivors of the disease.
Tibolone isn't available in the United States but is approved in 90 countries for easing menopausal symptoms and approved in 55 countries as an osteoporosis treatment. Many breast cancer patients use the drug to counteract the effects of early menopause caused by cancer treatments.
The new findings indicate that the drug should not be prescribed to any woman with known, past, or suspected breast cancer, said Prof. Peter Kenemans, of the VU University Medical Center in Amsterdam, Netherlands, and colleagues.
Tibolone acts like the female hormones estrogen and progesterone in relieving menopausal symptoms. But, unlike estrogen and progesterone, it has been believed that tibolone would reduce the risk of some cancers.
This study included almost 3,100 women who'd had surgery for breast cancer. The women were randomly assigned to receive either 2.5 milligrams of tibolone a day or a placebo. The women's mean age at the start of the study was 52.7 years and the mean time since surgery was 2.7 years.
Among the 1,556 women taking tibolone, 237 (15.2 percent) experienced a cancer recurrence, compared with 165 (10.7 percent) of the 1,542 women taking the placebo. That meant that women taking tibolone had a 40 percent increased risk of recurrent cancer. The researchers also found that 70 percent of the recurrences among the women taking tibolone were distant metastases, which are usually fatal.
This increased risk associated with tibolone was so serious that the study was halted six months early. The findings were released Tuesday by The Lancet Oncology.
The researchers noted that the study had a number of limitations -- breast cancer risk factors weren't assessed and detailed analyses weren't conducted on primary tumors. The study authors also said the profile of future groups of breast cancer patients may differ from that of those in this study. For example, tamoxifen use might not be as widespread or patients might be undergoing adjuvant systemic therapy.
Nevertheless, the study authors concluded, "There are insufficient data to establish the safety of tibolone in women who have had breast cancer and do not require or have finished adjuvant therapy."
This is just the latest study to raise concerns about tibolone. A U.S. study released last summer found that women 60 and older who took tibolone to relieve menopausal symptoms were 2.2 times more likely to suffer a stroke than those taking a placebo. The finding prompted an early halt to that study, which was published in the New England Journal of Medicine.
But that same study also found that women taking tibolone had a reduced risk of breast cancer and colon cancer.
The U.S. National Women's Health Information Center has more about menopause treatment
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