"The updated side effects analysis shows no new adverse events and no increased death rate is found with tamoxifen," said principal investigator Ivana Sestak, MS, doctoral candidate and cancer researcher, Cancer Research UK (CRUK), the Wolfson Institute of Preventive Medicine, London, United Kingdom. "Most adverse effects associated with tamoxifen occur early on. Although very large numbers of side effects were reported, we identified no new safety concerns."

Dr. Sestak, who presented the findings on March 22^nd, worked with senior investigator Jack Cuzick, PhD, head of mathematics, statistics, and epidemiology, Imperial Cancer Research Fund, London, UK.

The researchers reviewed the follow-up data from the International Breast Cancer Intervention Study-I (IBIS-I) data to address concerns about tamoxifen safety issues. They particularly wanted to know whether the adverse effects associated with tamoxifen discourage its use as a chemopreventive agent.

The original IBIS-I study involved 7154 women who were at increased risk of breast cancer, who were either randomised to 5 years of tamoxifen therapy at a dose of 20 mg per day or placebo. At semi-annual follow-up visits, patients gave detailed information regarding any adverse effects that they experienced. Treating physicians documented the adverse effects and evaluated them according to follow-up time, severity, and use of hormone replacement therapy.

Among the original recruits, 95.4% of women completed treatment. Although many women in both the treatment and placebo arms reported adverse events, "the only major categories that showed significant differences were vasomotor and gynecological side effects," Ms. Sestak said. These occurred at a rate that was approximately 12% higher in the tamoxifen group than the placebo group, she said.

In the overall group, 607 of the women in the tamoxifen group reported any type of breast problems, compared with 830 in the placebo group, so that such events were 27% less likely to occur in the tamoxifen group (P <.0001). Women taking tamoxifen were also less likely to report breast cysts and pain (P <.0001 for each).

However, those in the tamoxifen group were more likely to report brittle nails (P =.0003). Among these participants, 54 women in the tamoxifen arm and 44 in the placebo arm died from any cause, Ms. Sestak added, although this difference was not statistically significant.


[Presentation title: International Breast Cancer Intervention Study I: Updated Side Effects Analysis. Abstract 11]

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