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Study Finds Tamoxifen May Significantly Increase Risk of Uterine Cancer (dateline September 14, 2000)

The drug tamoxifen has been used for over 20 years to help treat breast cancer.  Recently, tamoxifen has also been approved by the U.S. Food and Drug Administration (FDA) to help prevent breast cancer in women at high risk for the disease. Though researchers have known for some time that tamoxifen can increase a woman’s risk of endometrial cancer (cancer of the lining of the uterus), a new study from the Netherlands finds that long-term use of tamoxifen may increase the risk for endometrial cancer by as much as 50%. Therefore, the researchers are cautioning physicians to think carefully before prescribing tamoxifen to healthy women as a preventive measure.

According to the study, which is published in the September 9, 2000 issue of The Lancet, women who take tamoxifen for two to five years could be at a significantly higher risk of developing endometrial cancer than women who do not use tamoxifen. The researchers also found more cases of advanced endometrial cancer among women in the study who had taken tamoxifen for two or more years (compared with non-users). While women who are diagnosed with early-stage endometrial cancer generally have good prognoses (expected outcomes), the prognosis for advanced endometrial cancer can be far worse.

Therefore, lead researcher Karen Gelmon, MD, of the British Columbia Agency in Vancouver, Canada, and her colleagues conclude that healthy women may want to avoid taking tamoxifen unless they are participating in a clinical trial.  However, for women with breast cancer, the researchers say that the benefits of tamoxifen typically outweigh the risks of endometrial cancer.

While the results of the study show a 50% increase in endometrial cancer risk for women who take tamoxifen for over two years, the researchers caution that future research is needed to confirm these results. According to Dr. Gelmon, the study took a retrospective look at the patients’ data. Some data on healthy women may not have been available, which could have caused an inflated view of the number of women with endometrial cancer.

Nevertheless, the findings of this study suggest that physicians should carefully weigh the benefits and risks of tamoxifen before prescribing it to healthy women to help reduce the risk of breast cancer. The researchers maintain that tamoxifen can be highly effective in treating advanced breast cancer as well as preventing the disease in women at high risk. This study should not cause women with breast cancer to stop taking tamoxifen, said the researchers.

However, patients should be made aware of all possible benefits and risks of tamoxifen. Women should also report any changes in their health (such as vaginal bleeding or pelvic pain) to their physicians immediately. Researchers are investigating whether women on tamoxifen should receive annual vaginal ultrasound exams to screen for endometrial problems.

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