Research findings help predict risk of blood clots in women receiving tamoxifen therapy for breast cancer

May 15 2005

New research findings may help physicians determine which women have an increased risk of blood clots when taking tamoxifen for the management of breast cancer, a team led by Dana-Farber Cancer Institute investigators will report at the American Society of Clinical Oncology's annual meeting.

Dana-Farber's Judy Garber, MD, MPH, will present the study's data (Abstract 508) - on behalf of her colleagues at Yale University School of Medicine and more than 30 institutions and medical practices in the Cancer and Leukemia Group B consortium, a clinical research network organized by the National Cancer Institute - during an oral presentation on Sunday, May 15, at 8 a.m., Level 2, Hall A2.

The study involved more than 300 women receiving tamoxifen as "adjuvant" therapy - given after a new breast cancer diagnosis to prevent recurrence. Researchers focused on a blood-clotting protein called Factor V. Previous studies had shown that women with a specific Factor V gene mutation - which gives rise to an abnormal version of the protein, known as Factor V Leiden (FVL) - are at increased risk for blood clots when pregnant or taking oral contraceptives or estrogen replacement therapy.

In the new study, researchers found that women who had blood clots while taking tamoxifen were almost four times as likely to have an FVL mutation as were those who did not have blood clots. The results suggest that testing women in advance for FVL mutations may enable physicians to identify some women who should either use alternatives to tamoxifen or, if good alternatives are not available, use a blood thinner while taking tamoxifen.

"Other factors contributing to blood clot risk must also be considered in the decision to recommend tamoxifen to generally healthy women, including a history of previous blood clots, obesity and planned surgery," says Garber. "But FVL testing can now be used to help make this powerful medication safer for some women who need it for breast cancer treatment or prevention."