However, the study in the Oct. 20 issue of the Journal of the National Cancer Institute does link stroke to another aspect of cancer treatment: chemotherapy. Use of chemotherapy was associated with increased risk of stroke in the study, regardless of whether women took tamoxifen or not.
"The finding that chemotherapy increases stroke risk among women treated for invasive breast cancer was unexpected, and we do not know whether this result is because women receiving chemotherapy have more advanced disease-and persistent cancer increases their likelihood of developing clots in their blood vessels-or if the chemotherapy itself accelerated atherosclerotic disease," says study senior author Leslie Bernstein, Ph.D., professor of preventive medicine and AFLAC Chair in Cancer Research at the Keck School of Medicine of the University of Southern California.
"In absolute terms, the risk of a stroke following breast cancer diagnosis is small, and our findings should not deter women from this treatment. Chemotherapy remains a key component of breast cancer therapy," she adds.
Oncologists have prescribed tamoxifen to treat postmenopausal breast cancer since 1978. Since then, the drug has also been shown to reduce the risk of cancer in the opposite breast, as well as breast cancer recurrence. It also cuts breast cancer risk in half among women considered at high risk for the disease. However, tamoxifen use may have potential, serious side effects. One of those side effects, an increased risk of stroke, was seen in two large randomized trials but not in other studies.