Adjuvant Tamoxifen for 10 Years Better Than 5 Years in ER-Positive Breast Cancer

Bonnie Gillis
Published Online: Wednesday, December 5, 2012
Dr. Richard Gray

Photo Courtesy © SABCS/Todd Buchanan 2012

Richard Gray, MSc
Extending the duration of adjuvant tamoxifen treatment to 10 years was more effective than the standard 5 years of treatment in protecting against recurrence and death among women with estrogen receptor-positive (ER+) breast cancer. The international ATLAS study showed that 10 years of tamoxifen reduced the risk of dying by 29% during the second decade after diagnosis compared with 5 years of treatment. These findings were presented at the 2012 CTRC-AACR San Antonio Breast Cancer Symposium.

“We already knew that 5 years of tamoxifen was very effective and has a carryover effect after stopping, with about a 30% reduction in mortality over the next 5 years. We wanted to do a longer-term treatment trial on tamoxifen to see if we could beat the carryover effect of 5 years of treatment,” said Richard Gray, MSc, Clinical Trial Service Unit, University of Oxford, Oxford, U.K. Gray presented the results on behalf of lead author  Christina Davies, MD, also of the University of Oxford.

ATLAS enrolled 6846 women with ER+ breast cancer between 1996 and 2005. Approximately half the women had node-positive disease, and all had been taking tamoxifen for 5 years. Women were randomized to 5 more years of tamoxifen or no more tamoxifen.

After about 8 years of follow-up, 1328 recurrences and 728 deaths after recurrence were reported. Treatment assignment had little or no effect on rates of recurrence or death in the period 5 to 9 years after diagnosis. However, in the second decade after diagnosis, women who continued on tamoxifen had a 25% lower recurrence rate and 29% lower breast cancer mortality rate compared with women who stopped after 5 years of tamoxifen.

The risk of dying due to breast cancer 5-14 years after diagnosis was 12.2% for continuing tamoxifen users versus 15% for those who only had 5 years of treatment, representing an absolute gain of 2.8% favoring continuing treatment with tamoxifen for 10 years.

“Little effect was seen for longer duration of tamoxifen during the years 5-9 after diagnosis,” Gray said. “The greatest benefit was observed during 10 – 14 years after diagnosis.”

A significant benefit for 10 years versus 5 years of tamoxifen was observed for recurrence (rate ratio[RR] = 0.75 10 years of treatment versus RR = 0.90 for 5 years, P = .002) and breast cancer mortality (RR = 0.71 in 10 years of treatment versus RR = 0.97, P = .01).

Based on the results of this trial, the estimated effect that 10 years of tamoxifen versus no tamoxifen in ER+ breast cancer could have is to cut the rate of breast cancer deaths by 48% 10 years after diagnosis, Gray said.

Receiving tamoxifen for a longer period of time can increase side effects, including endometrial cancer. The cumulative risk of death from endometrial cancer between 5-14 years after diagnosis was 0.4% for the continuing tamoxifen users versus 0.2% for those who did not continue.

Gray said that the reduction in breast cancer deaths outweighs the risk of endometrial cancer and other side effects of tamoxifen. No apparent excess risk of endometrial cancer was observed in younger women in the trial on continued tamoxifen.

To put this in perspective, Gray said that the absolute mortality gain of 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.

“Women and their doctors should be aware of the evidence from ATLAS when deciding how long to continue tamoxifen or other endocrine treatment,” he said.


Davis C, Hongchao P, Godwin J, et al. ATLAS. 10 v 5 years of adjuvant tamoxifen (TAM) in ER+ disease: effects on outcome in the first and in the second decade after diagnosis. Presented at: 2012 CTRC-AACR San Antonio Breast Cancer Symposium; December 4 – 8, 2012; San Antonio, Texas. Abstract S1-2.

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