Study Shows Tamoxifen a Blessing for Many -- a Curse for a Few
Sept. 7, 2000 -- Tamoxifen has been seen as a savior for breast cancer survivors and women at high risk for the disease, and its use has been increasing in recent years. But a new study shows that women who take the drug need to be watched carefully for dangerous types of cancer of the uterus. However, the researchers still feel that, in breast cancer survivors, the benefits of the drug are worth the risk.
The benefits of tamoxifen for treatment of breast cancer are still far greater than the slightly increased risk of cancer of the uterus, lead researcher Flora E. van Leeuwen, PhD, tells WebMD. "For 1,000 women with breast cancer who take tamoxifen for five years, about 90 deaths from breast cancer will be prevented over 10 years. Tamoxifen will induce about 20 excess cases of cancer [of the uterus], but only four of these will be fatal," says van Leeuwen, who is head of the department of epidemiology at The Netherlands Cancer Institute in Amsterdam.
Since breast cancer grows in response to the hormone estrogen, tamoxifen, which blocks the effects of estrogen, has been used for many years to prevent relapse in breast cancer survivors. Recently, tamoxifen also was approved to help prevent a first episode of breast cancer in otherwise healthy women with a strong family history of breast cancer.
It's been known for several years that tamoxifen increases the risk of cancer of the uterus, but this new study shows that women who take the drug may be more likely to develop very aggressive types of uterine cancer.
The Dutch researchers report that when breast cancer survivors who have taken tamoxifen develop uterine tumors, the tumors are likely to be more dangerous than those in women who did not take tamoxifen. Consequently, these women were more likely to die of uterine cancer than were women who had not taken tamoxifen, and that risk increased with the amount of time on tamoxifen.
The study, which reviewed more than 300 breast cancer survivors who took tamoxifen, also resurrects questions about the wisdom of using tamoxifen as a preventive treatment in healthy women who do not have breast cancer but are thought to be at high risk due to family history or genetic factors. The FDA approved tamoxifen for this use in 1998, but it is not approved in the U.K. or in most European countries for use in healthy women, even those at high risk for breast cancer.
Cynthia Pearson, executive director of the National Women's Health Network, testified against approval at the 1998 FDA advisory committee hearings. Pearson tells WebMD, "The van Leeuwen data provide some support for our contention that it doesn't make sense to try to prevent one cancer by using a drug that causes another cancer. During the approval hearings, some experts contended that the [uterine] cancers caused by tamoxifen were relatively 'good' and curable cancers. This study provides evidence to the contrary."