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Title: Anastrozole Less Likely to Cause Venous Thromboembolism Than Tamoxifen: Presented at SABCS

"Anastrozole Less Likely to Cause Venous Thromboembolism Than Tamoxifen: Presented at SABCS"

By Paula Moyer SAN ANTONIO, TX -- December 19, 2006 -- Patients treated with anastrozole (Arimidex) are much less likely to develop venous thromboembolisms (VTEs) than are patients treated with tamoxifen in adjuvant treatment for early breast cancer, according to investigators who presented their findings here at the 29[^th Annual San Antonio Breast Cancer Symposium (SABCS).

"We found the greatest risk in the initial treatment period but it persisted throughout the 5 years," according to principal investigator Jack Cuzick, MD, John Snow professor of epidemiology, Wolfson Institute of Preventative Medicine, London, United Kingdom. "This difference in risk represents a major long-term safety benefit for anastrozole compared with tamoxifen in the adjuvant treatment of early breast cancer."

Dr. Cuzick and colleagues based their findings on an analysis of data from the Arimidex, Tamoxifen, Alone or in Combination (ATAC) trial. In the study, patients were treated with either agent alone or in combination for 5 years. The study involved 9,366 postmenopausal women with early invasive breast cancer.

Although the combination arm was discontinued because of the lack of benefit, the investigators continued to follow those women, Dr. Cuzick said in a presentation on December 15^th.

After a median of 68 months, 382 women had at least 1 VTE. An analysis of the most serious events for each patient showed 51 pulmonary emboli, 147 deep vein thromboses, 6 retinal vein thromboses, and 178 cases of superficial thrombophlebitis.

The women in the combination arm had similar rates of adverse events to those in the tamoxifen arm, for an odds ratio of 1.10. However, the anastrozole group had an incidence rate of VTEs that was 39% lower, for an odds ratio of 0.61 (P < .0001). In the tamoxifen and combination groups, the risk was highest at the start of treatment but continued to be higher throughout the duration of treatment.

"The strongest single risk factor for VTE was immobility due to major surgery, fracture, or infection in the 6 months before starting treatment," according to Dr Cuzick. Immobility was linked to an odds ratio of 4.62 (P < .0001), and had occurred before VTE in 57 cases (14.9%). When the investigators adjusted for risk factors, the risk associated with each treatment was unchanged, he said.

[Presentation title: A Detailed Analysis of the Benefits of Anastrozole Over Tamoxifen for Venous Thromboembolic Events (VTEs) After 5 Years Treatment. Abstract 104]

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