Ten years of adjuvant treatment with tamoxifen provided women who had estrogen receptor-positive breast cancer greater protection against late recurrence and death from breast cancer compared with the current treatment standard of five years, according to a study.
The data came from the international Adjuvant Tamoxifen — Longer Against Shorter study, also known as ATLAS.
“Five years of adjuvant tamoxifen is already an excellent treatment that substantially reduces the 15-year risk for recurrence and death from estrogen receptor-positive breast cancer, but ATLAS now shows that 10 years of tamoxifen is even more effective,” Christina Davies, MD, of the University of Oxford in the United Kingdom, said in a news release.
“The main additional benefit from continuing tamoxifen treatment is to reduce breast cancer mortality during the second decade after diagnosis.”
Davies said whereas a five-year treatment regimen reduces breast cancer mortality in that late period by almost a third when compared with no tamoxifen treatment, a 10-year course approximately halves breast cancer mortality during the second decade after diagnosis.
The researchers enrolled 6,846 women with ER-positive breast cancer between 1996 and 2005. Half had node-positive disease. All the women had been using tamoxifen for five years, and the researchers randomly assigned them to continue treatment for another five years or to stop immediately.
The treatment allocation had little effect on either recurrence rates or death rates during the period spanning five to nine years after diagnosis. However, during the second decade following diagnosis, the women who continued tamoxifen treatment had a 25% lower recurrence rate and a 29% lower breast cancer mortality rate compared with women who stopped after five years.
Risk for death from breast cancer five to 14 years after diagnosis was 12.2% among those who continued use versus 15% among those who stopped. The researchers observed the greatest benefit during the period spanning 10 to 14 years after diagnosis.
Davies noted that continuing tamoxifen use can increase side effects, with endometrial cancer being the most life-threatening. Because endometrial cancer is generally curable, the cumulative risk for death between five and 14 years after diagnosis was 0.4% among those in the 10-year treatment group versus 0.2% among those in the five-year treatment group.
Because this risk is heavily outweighed by the reduction in breast cancer deaths, overall mortality was significantly reduced by longer treatment, the researchers noted. In premenopausal women, for whom tamoxifen is often the endocrine treatment of choice, there was no apparent excess of endometrial cancer.
“Many women with ER-positive breast cancer take tamoxifen, or some other adjuvant endocrine treatment, but the current recommendation is to stop after five years,” Davies said. “ATLAS showed that protection against breast cancer recurrence and death is greater with 10 years than with five years of tamoxifen use. Women and their doctors should be aware of this evidence when deciding how long to continue tamoxifen or any other endocrine treatment.”
The study appeared Dec. 5 on the website of The Lancet and was scheduled for presentation at the CTRC-AACR San Antonio Breast Cancer Symposium. The study abstract is available at http://bit.ly/YzYeYv.