Health officials are warning older women who are taking the drug tamoxifen to prevent breast cancer that it may put them at increased risk of cancer of the uterus, stroke and blood clots in the lungs.
“These risks apply specifically to elderly women on the drug and not to younger women taking tamoxifen for the prevention of breast cancer,” says Dr. Paul Goss, director of the breast cancer prevention program at Princess Margaret Hospital.
“These side effects are extremely rare.”
Goss emphasized this warning doesn’t apply to any patient who has had a diagnosis of breast cancer, in whom “the benefits of tamoxifen far outweigh the risk” in all age categories.
“Tamoxifen is an established gold standard of care for many breast cancer patients,” he said. “People on the drug, following a diagnosis for breast cancer, should not consider stopping their treatment based on this information.”
Breast cancer claims the lives of 5,400 Canadian women and 40 men each year. Only 5 to 10 per cent of the causes of all breast cancer cases can be traced back to genetics. In the majority of cases, the causes are unknown.
High-risk patients who are using tamoxifen in an effort to prevent breast cancer, and their doctors, should talk about the potential side effects, said Ryan Baker, spokesperson for Health Canada.
“For the prevention of breast cancer the benefits may no longer outweigh the risks,” he said.
Taken in pill form, tamoxifen works against the effects of estrogen on breast cancer cells. Estrogen promotes growth in these cells. The drug slows, or halts, the growth.
If patients taking the drug experience any side effects such as weakness or numbness in the face, arms or legs, problems with speech or vision, chest pain, leg swelling, abdominal pain or abnormal vaginal bleeding, they should contact their doctor immediately, warns Health Canada.
Tamoxifen has also been used for more than 20 years to treat patients with advanced breast cancer, according to the U.S. National Cancer Institute’s Web site.
The National Cancer Institute has funded a large research study into the usefulness of tamoxifen in preventing breast cancer in high risk women. The study has found an almost 50 per cent reduction in the diagnoses of invasive breast cancer among women taking the drug.