Ten Years of Tamoxifen May Be Better than Five, but Questions Remain

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Early results indicate that breast cancer survivors who take tamoxifen for longer than five years appear to have a lower rate of recurrence, although the data is still too incomplete to draw conclusions, researchers reported Friday evening at SABCS.

The analysis is based on an international study of 11,500 women, all of whom had taken tamoxifen for five years. At the beginning of the study, half the women were told to continue taking tamoxifen for an additional five years, and half were advised to stop.

The research is designed to answer a question on the minds of many patients and their physicians: If five years of tamoxifen can reduce the risk of cancer recurrence, will 10 years lower the risk even more? The official recommendation now is that more than five years offers no additional benefit, but scientists, like Sir Richard Peto, PhD, of the University of Oxford in England, question this conclusion.

In Friday's discussion, Peto reported that, so far, more than 1,500 women in the study have relapsed; 825 of those have occurred among the women who stopped tamoxifen at five years and 739 among women who continued the drug. However, these results are still preliminary — no one can say what will happen as time passes — and are not different enough to comfortably say they are not due to chance. There is also the issue of the adverse effects that come with tamoxifen, including a slight increased risk of cataracts, blood clots, and endometrial cancer.

"We're trying to answer the question of what 10 years of treatment will do to the 20-year outcome," Peto says. "We really need much longer observation." —Laura Beil