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Ten Years of Tamoxifen Better Than Five: Presented at SABCS

By Janet Fricker

SAN ANTONIO, TX -- December 17, 2007 -- The recommendation to limit adjuvant tamoxifen treatment to 5 years may have been premature, suggest results of a study presented during a late breaking special session here at the 30th Annual San Antonio Breast Cancer Symposium (SABCS).

The Adjuvant Tamoxifen: Longer Against Shorter (ATLAS) trial, a large international study, compared the efficacy and safety of 5 years versus 10 years of adjuvant tamoxifen treatment. In the study 11,500 women from 400 international centers who had been taking tamoxifen for 5 years were randomized at year 5 to continue taking tamoxifen to 10 years or to stop treatment.

Presenting the data, Sir Richard Peto, MD, Clinical Trials Unit, University of Oxford, Oxford, United Kingdom, pointed out the limitations of the study. Only 59% of the patients were definitely estrogen-receptor (ER)-positive; the remaining 41% were not tested for ER status.

Of the untested women, around one quarter are likely to have been ER negative, and hence are unlikely to experience benefits from tamoxifen. In addition there were site-to-site differences in compliance rates, Sir Richard said.

"The upshot is that ATLAS only shows around 72% of the true effect of tamoxifen," he said.

Nevertheless, despite such limitations, results show that a trend towards decreased recurrence and breast cancer mortality is beginning to be seen at 5-plus years in the 10-year tamoxifen group compared with the 5-year tamoxifen group.

"This interim analysis does make it very likely that continuation of tamoxifen would produce clinical benefit," said Sir Richard, adding that the current recommendations to limit tamoxifen treatment to only 5 years, which were based on data from National Surgical Adjuvant Breast and Bowel Project (NSABP) study B14, is likely to have been premature.

"The numbers in NSABP B14were too small to justify dismissing the important question of whether continuing tamoxifen beyond 5 years could, in the long run, moderately reduce the recurrence rate," said Sir Richard. "The new ATLAS data suggest that longer-term use is likely to produce benefits."

The ATLAS data, he added, is likely to be of relevance to the duration of the newer aromatase inhibitor (AI) hormonal treatments for breast cancer.


[Presentation title: ATLAS (Adjuvant Tamoxifen, Longer Against Shorter): International Randomized Trial of 10 Versus 5 Years of Adjuvant Tamoxifen Among 11 500 Women - Preliminary Results. Abstract 48]

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