New research shows no increased risk of stroke from taking tamoxifen (search), a drug used to fight breast cancer.

However, older women taking chemotherapy (search) should be watched closely for stroke (search) symptoms, researchers say.

The paper appears in the latest issue of the Journal of the National Cancer Institute.

It comes on the heels of research published just a week ago: A study found an opposite conclusion: a small but real stroke risk among women taking tamoxifen.

In that study, researchers analyzed nine previous studies and showed that tamoxifen was associated with an 82 percent increase in ischemic (search) (clot-related) stroke risk and a 28 percent increase in risk for all strokes.

This newest study found no link between tamoxifen and stroke — no matter how long patients took tamoxifen, how recently, or how big the dosage was, reports lead researcher Ann M. Geiger, MD, with Kaiser Permanente Southern California in Pasadena.

However, she did not report such good news regarding chemotherapy.

Tamoxifen, Chemo: Looking for Stroke Risk

Though tamoxifen is known to decrease the risk of breast cancer, one specific concern with tamoxifen has been its potential association with blood clots — particularly whether or not it can increase the risk of a stroke.

In their study, Geiger and her colleagues thoroughly analyzed medical, hospital, and death records for 179 breast cancer patients who had suffered strokes. The average age of the women was 67.

They compared the data with similar records for breast cancer patients who had not suffered a stroke.

Women taking tamoxifen did not have higher stroke risk, Geiger reports. However, chemotherapy did increase stroke risk, although researchers could not pinpoint the specific type of chemotherapy causing this risk.

Women who had received chemotherapy were two to three times more likely to have stroke.

Women with a history of high blood pressure or diabetes and who were taking medication to treat those health problems had the highest risk, she writes.

It's not clear what's happening with chemotherapy to increase stroke risk, she writes. Their breast cancer may be more aggressive, triggering artery damage and blood clots. Also, drugs used with chemotherapy might somehow increase stroke risk.

"Our study suggests that women and their [doctors] considering tamoxifen for breast cancer can do so without concern for stroke," Geiger writes. Any risk from chemotherapy must be "balanced against the life-extending benefits of chemotherapy."

Tamoxifen Experts Weigh In

Geiger's research group "is a very good epidemiological group," says Ruth M. O'Regan, MD, director of translational breast cancer research at Emory University's Winship Cancer Center in Atlanta. "I would consider this a 'real' finding regarding tamoxifen. And if you look at previous data, there is a slightly increased risk of stroke, but it's not as conclusive as other risks like [lung blood clots]."

The chemotherapy/stroke findings "surprised me most," O'Regan tells WebMD. "I'm not aware of any stroke increase with chemotherapy. But we must keep in mind this is one study, and this hasn't been shown before. I don't think you can make much of this."

She advises women over age 60 to see an internal medicine doctor regularly and to keep an eye on their stroke and other health risk factors. Factors that increase heart disease — high cholesterol, high blood pressure, and smoking — also increase the risk of stroke.

"Patients should be relieved about tamoxifen," says Paul Tartter, MD, professor of surgery at St. Luke's-Roosevelt Comprehensive Breast Center and Columbia University College Physicians and Surgeons in New York. "This rings with my clinical experience. I've got several thousand women in my practice and I rarely, rarely see a stroke. In fact, I don't remember ever seeing a stroke in someone taking tamoxifen."

The chemotherapy finding "worries me a little bit," Tartter tells WebMD. "It also surprises me, because someone getting chemotherapy would have low platelet count." Since platelets help the blood clot, having fewer of them should theoretically provide an anticlotting effect, which would help prevent stroke, he says. "This needs to be investigated further to find the biological explanation for it."

By Jeanie Lerche Davis, reviewed by Michael W. Smith, MD

SOURCES: Geiger, A. Journal of the National Cancer Institute, Oct. 20, 2004; vol 96: pp 1528-1536. Ruth M. O'Regan, MD, director of translational breast cancer research, Emory University's Winship Cancer Center, Atlanta. Paul Tartter, MD, professor of surgery, St. Luke's-Roosevelt Comprehensive Breast Center and Columbia University College Physicians and Surgeons, New York. WebMD Medical News: "Tamoxifen Side Effect: Higher Stroke Risk."