Tamoxifen use is iffy for many women
Breast cancer preventative has huge risks
Used for nearly 20 years as an alternative to chemotherapy for breast cancer treatment, tamoxifen's new indication to prevent disease comes with a laundry list of caveats.
"This is not the drug for the average woman. It's not the prevention that we've all been demand ing," says Fran Visco of the National Breast Cancer Coalition in Washington, DC. Why not? Simply put, the risks can outweigh the benefits. The known risks include blood clots and uterine cancer. Both could be as deadly as breast cancer itself.
Researchers won't be able to answer several questions until more long-term studies are done. For example, it's unclear whether patients will have to take the drug for their lifetime to ensure prevention of malignancies, or whether the drug's potency will remain high over the long run. And based on clinical trials, there is the suggestion that any new tumors that may develop while a patient is on tamoxifen may be harder yet to treat.
NCI study seeks answers
To deal with those issues, organizations such as the National Cancer Institute (NCI) have developed strict patient profiles and recommendations for the drug. Women over 50 who have had breast cancer or precancerous lesions, have two or more close relatives with the disease, or have had lobular carcinoma in situ, should consider taking it.
Women who have had a hysterectomy are at lower risk, while women over 50 have the greatest chance of being stricken with the most dangerous side effects. Daniel Dubovsky, MD, an oncologist at St. Joseph's Hospital of Atlanta, adds that women who have had a pulmonary embolism or have obvious blood clotting risk factors or a family history of endometrial cancer also may be high-risk candidates for tamoxifen. "This is not for women at large but for those women with a risk equivalent of a 60-year-old," he says. He recommends that potential patients under go a risk analysis before being given the drug.
As for the duration of taking tamoxifen as a preventative measure, Dubovsky agrees only that further study can answer that question.
It's clear that for women who fit the criteria, tamoxifen could be a lifesaver. In 1992, 13,338 women began taking tamoxifen or placebo in a federally funded study sponsored by the National Institutes of Health. Included in the trial were women with relatives who had breast cancer, those who had a late pregnancy or experienced previous biopsies or benign but suspicious lumps, or simply those over 60. Patients on the drug had a 45% lower incidence of malignancies, compared with those on placebo. The results were so positive the trial was stopped in mid-April, 13 months ahead of schedule, so the placebo group could be given the opportunity to begin taking the drug.
The trial results nearly matched the kind of reaction researchers stumbled onto in the 1980s during a study of tamoxifen's treatment efficacy, where it was found that along with treating and beating recurrences of breast cancer, patients on the drug also experienced about half as much new cancer in their other breast than those on chemotherapy or another type of treatment.
Dubbed a designer estrogen, tamoxifen works by locking onto the same cell receptors as estrogen, blocking the natural hormone from attaching and then stimulating cancer cells in the breast. But in the uterus, tamoxifen attaches onto cell receptors and does stimulate cancer cells, mimicking estrogen. Exactly why is unknown and is part of the ongoing research into the drug.
Research into another designer estrogen, raloxifene (see related story, p. 107) is anticipated as the drug has shown equally remarkable abilities to prevent breast cancer in older women, but is not plagued by the clotting or uterine cancer risks inherent with tamoxifen. The drug is new to the market and has only been approved for the prevention of osteoporosis.
"We have to caution that our data are very preliminary. Raloxifene seems to reduce the risk of breast cancer somewhere between 60% and 80%, depending on how the data have been analyzed," says Robert Lindsay, MD, of the National Osteoporosis Foundation. The drug's benefits against breast cancer were found during osteoporosis studies, while research solely into raloxifene's prevention capabilities is just three years old, he adds. Further testing is scheduled to begin later this year.
[For more information, contact the National Breast Cancer Coalition at (800) 622-2838, the NCI at (800) 601-9242, or the National Osteoporosis Foundation at (202) 223-2226.]
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