Tamoxifen Truths

Perhaps you've had breast cancer that was successfully treated, and your doctor has mentioned taking tamoxifen to try to keep it from coming back. Maybe your doctor wants you to take it during your actual treatment. Or maybe you're at a high risk for getting the disease, and your doctor has given it to you to help prevent it in the first place.

But what is tamoxifen, and how does it work?

Tamoxifen is a drug in pill form (sometimes known by the trade name Nolvadex) that interferes with the activity of estrogen in the breast. It's been used for two decades to treat breast cancer. The drug, a synthetic hormone, also is used to deter recurrence of breast cancer in women who have already had a tumor, and is under investigation to prevent breast cancer in women at high risk for it, said Leslie Bernstein, Ph.D., USC professor of preventive medicine and AFLAC Chair in Cancer Research.

Many breast cancer cells need estrogen, a natural female hormone, to grow. When tamoxifen enters the body, it competes with estrogen to interact with breast cancer cells, creating a sort of protection against the cells' reproduction.

Because tamoxifen acts like estrogen in other systems of the body, it may be beneficial to health in other ways. It may act like estrogen replacement therapy in menopausal women, reducing cholesterol in the blood and slowing bone loss due to osteoporosis.

But tamoxifen isn't for everyone. Although national trials have shown it to be effective in preventing recurrence of cancer in women who have already had a tumor and preventing a new tumor in the opposite breast, as well as reducing the risk of breast cancer among women at risk for the disease, no studies have shown that tamoxifen helps women who are at ordinary risk for the disease.

Tamoxifen slightly increases the chance of blood clots in the legs or lungs of women who take it. The risk is similar to that faced by women who take estrogen replacement therapy.

It also has been shown to increase the chance of getting endometrial cancer. Women taking tamoxifen face a 50 percent greater risk of getting endometrial cancer than those not taking it, with risk increased further still among those who also have taken estrogen replacement therapy and are overweight, Bernstein said.

Women taking tamoxifen also may have some vision problems.

Other possible complications are under study, including whether women who take tamoxifen have higher stroke risk. Side effects may be similar to menopausal symptoms: hot flashes, vaginal discharge and the like.

Although tamoxifen has been shown to raise the risk of endometrial cancer, that needs to be weighed against the risks of getting breast cancer.

The incidence of endometrial cancer in the United States is far lower than that of breast cancer, and women are more likely to die of breast cancer than endometrial cancer. Endometrial cancer may be caught early, as well, by recognizing symptoms such as abnormal vaginal bleeding and pelvic pain.

Women need to discuss all the facts about tamoxifen and their risk for breast and endometrial cancer with their doctor before making a decision to take the medication, Bernstein said, and physicians should be especially vigilant in monitoring patients who take tamoxifen and have additional risk factors such as obesity and a history of taking estrogen replacement therapy.