Preventive therapy through Tamoxifen usage

Tamoxifen is a medication that appears to block the action of estrogen in the breast. On the other hand, it appears to have some estrogen-like effects on some other tissues, including the uterus and the bones. It is not a new drug. Doctors have been prescribing it for breast cancer patients for more than 20 years. More recently, healthy women who are at high risk for the disease are requesting information about Tamoxifen as a preventive therapy for breast cancer. A large study, the Breast Cancer Prevention Trial (BCPT), has shown that Tamoxifen can decrease the risk of developing breast cancer in women ages 35 and older at elevated risk for the disease.

Women patients will need your help to make an individual decision for or against Tamoxifen as a preventive treatment. Risks for breast cancer and for Tamoxifen therapy must be weighed against benefits in light of an individual's age and medical history.

Benefits and Risks

In the Breast Cancer Prevention Trial, a large clinical trial conducted by the National Surgical Adjuvant Breast and Bowel Project and funded by the National Cancer Institute, a group of women were selected because of their high risk for invasive breast cancer. Participating women were randomized to see whether taking Tamoxifen could lower their risk of getting breast cancer. Women ages 35 and older who took a daily dose of 20 mg tamoxifen for up to 5 years had about 49 percent fewer diagnoses of invasive breast cancer compared to women who took a placebo. In women ages 35 to 49, risk of serious side effects appeared at a similar rate as in the group assigned to take placebos. However, benefits for women ages 50 and older came with important risks of serious side effects (increased risk for uterine cancer and blood clots).

The database used to determine which women were at high risk for breast cancer and, thus, eligible for the Tamoxifen prevention trial has been adapted to create this invasive breast cancer risk assessment tool.

Other Risks To Consider

Millions of American women meet the risk eligibility criteria used in the Breast Cancer Prevention Trial; namely, they are at least age 60 or have a 5-year risk for invasive breast cancer equal to or greater than that of the average 60-year-old woman, or 1.7 percent. Taking Tamoxifen to reduce one's risk of breast cancer may be a reasonable choice for many of these women, but it is not the best choice for all of them. The Breast Cancer Risk Assessment Tool will provide only part of the information you will need to counsel your patient. Weighing her age and accompanying medical history against known side effects will provide the other data needed for a complete and thoughtful assessment.

Tamoxifen Risks

In the Breast Cancer Prevention Trial, women ages 35 to 49 who were assigned to take Tamoxifen suffered side effects, such as increased risk for uterine cancer or blood clots, at a similar rate as those taking a placebo. So, for young women who met the high-risk criteria, Tamoxifen taken for the prevention of breast cancer offered benefit and no apparent increase in serious side effects. However, a woman should not take Tamoxifen during pregnancy because research in animals suggests that the drug may damage the fetus.

In the BCPT, women ages 50 and older who took Tamoxifen quadrupled their chances for getting uterine (endometrial) cancer, and tripled their chances for developing blood clots in their major veins or lungs.

Tamoxifen and Uterine Cancer

Overall, Tamoxifen therapy in the Breast Cancer Prevention Trial caused a 2.5-fold increase in uterine cancer. Increased risk was primarily in women ages 50 and older, who had about a 4-fold increase in incidence of this cancer. The risk of uterine cancer from Tamoxifen was similar to that for postmenopausal women who take estrogen replacement therapy. In the BCPT, for women ages 50 and older, the annual rate in the Tamoxifen arm was 30 cases of uterine cancer per 10,000 women compared to 8 cases per 10,000 in the placebo arm.

Of course, if a woman has had a prior hysterectomy for a benign condition, she is not at known risk for uterine cancer.