"Five years of adjuvant tamoxifen is already an excellent treatment that substantially reduces the 15-year risk for recurrence and death from estrogen receptor (ER)-positive breast cancer, but the trial now shows that 10 years of tamoxifen is even more effective," Dr. Christina Davies, a coordinator in the Clinical Trial Service Unit at the University of Oxford in England, said at the Cancer Therapy & Research Center-American Association for Cancer Research San Antonio Breast Cancer Symposium.
The study involved 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 study, also published in The Lancet, found after about eight years of follow-up, the researchers observed 1,328 breast cancer recurrences and 728 deaths after recurrence.
The treatment allocation had little effect on either recurrence rates or death rates during the period five to nine years after diagnosis. However, during the second decade following diagnosis, the women who continued tamoxifen treatment had a 25 percent lower recurrence rate and a 29 percent lower breast cancer mortality rate compared with women who stopped after five years, the study said.
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