Extending Adjuvant Tamoxifen to 10 Years Improves Survival

TON - February 2013, Vol 6, No 1 — February 21, 2013

Extending tamoxifen treatment for 10 years reduced the risk of dying by 29% compared with the standard 5 years of tamoxifen for estrogen receptor–positive (ER+) breast cancer, but these benefits of longer-duration tamoxifen did not emerge until the second decade after diagnosis, according to results of the international Adjuvant Tamoxifen—Longer Against Shorter (ATLAS) study.

“Five years of tamoxifen is very effective, and there is a carryover effect after stopping, with about a 30% reduction in mortality over the next 5 years. In the period 10 to 14 years after diagnosis, we found many fewer recurrences: 617 in the group receiving 10 years of tamoxifen versus 711 in patients treated with 5 years of tamoxifen. Breast cancer mortality and overall were similarly affected by longer duration of tamoxifen,” stated lead author Richard Gray, MSc, Clinical Trial Service Unit, University of Oxford, United Kingdom. He reported 331 breast cancer–related deaths in the 10-year group versus 397 in the 5-year group, and 539 versus 722 deaths from all causes, respectively.

ATLAS enrolled 6846 women with ER+ breast cancer from 36 countries between 1996 and 2005. About 50% had node-positive disease, and all women had been taking tamoxifen for 5 years. Women were randomized to either continue 5 more years of tamoxifen or to receive no more tamoxifen.

In the period 5 to 14 years after diagnosis, the risk of breast cancer death was 12.2% for 10-year users versus 15% for 5-year users, for an absolute gain of 2.8% favoring the longer treatment duration. In the second decade after diagnosis, those who took tamoxifen for 10 years had a 25% lower recurrence rate and a 29% lower breast cancer mortality rate compared with those who had only 5 years of tamoxifen.

The cumulative risk of death from endometrial cancer between 5 and 14 years after diagnosis was 0.4% for the continuing tamoxifen users versus 0.2% for those who did not continue.

“The reduction in breast cancer deaths far outweighs this small risk of endometrial cancer and other adverse events. Contrary to expectations, no excess risk of endometrial cancer was observed in younger women who took 10 years of tamoxifen,” Gray said. “The absolute mortality gain with 10 years of tamoxifen at 15 years after diagnosis is 12% or 1 in 8 balanced against 1 in 250 cases of endometrial cancer deaths,” he noted.

These findings are likely to be more relevant for premenopausal women. In the United States, postmenopausal women are generally given aromatase inhibitors (AIs), whereas tamoxifen is preferred for younger women with hormone receptor–positive breast cancer. However, some postmenopausal women are intolerant of AIs and may prefer to take tamoxifen, and the results are relevant for that group, stated Peter Ravdin, MD, director of the Breast Health Clinic at the Cancer Therapy & Research Center at the University of Texas Health Science Center in San Antonio. With any patient, risks versus benefits must be discussed, and low-risk women may prefer to stay with 5 years of treatment, he noted.

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