Results from the ATLAS study indicate that women with estrogen receptor (ER)-positive breast cancer should consider taking tamoxifen for up to 10 years after diagnosis.
Women who were randomly assigned to continue taking tamoxifen for a second 5-year period after initial treatment had a significantly lower risk for recurrence and breast cancer-related mortality in the second decade after their diagnosis than those whose treatment stopped after the conventional 5 years, reported Christina Davies (University of Oxford, UK) and co-workers at the San Antonio Breast Cancer Symposium in Texas, USA.
"Women and their doctors should be aware of this evidence when deciding how long to continue tamoxifen, or any other endocrine treatment," said Davies in a press release. The ATLAS study results were simultaneously published in The Lancet.
The ATLAS (Adjuvant Tamoxifen - Longer Against Shorter) trial included 6846 women with ER-positive breast cancer, half of whom had node-positive disease. Over an average of 7.1 women-years of follow-up, 1328 breast cancer recurrences were reported, including 900 cases in years 5-9 and 379 cases in years 10-14 after diagnosis.
The likelihood of recurrent disease was significantly lower in women assigned to receive tamoxifen for 10 years versus those given treatment for 5 years, with a rate ratio (RR) of 0.90 for years 5-9 and 0.75 after 10 years.
Extending tamoxifen treatment for 10 years was also associated with significantly lower breast cancer-related mortality, compared with treatment for 5 years (RR=0.97 during years 5-9 and 0.71 in later years).
In the 5-14 years after diagnosis, the Kaplan-Meier risks for recurrence with 10 and 5 years of tamoxifen were 21.4% versus 25.1%. For breast cancer-related mortality, the rates were 12.2% versus 15.0%.
Although tamoxifen is associated with an increased risk for uterine cancer, the researchers report that for women randomly assigned to treatment when aged 50 years or older the incidence in years 5-14 was still low, at 3.1%, for women taking tamoxifen for 10 years, compared with 1.6% for those taking the drug for only 5 years. The rate of uterine cancer mortality was 0.4% versus 0.2%.
For premenopausal women, who are unable to switch to aromatase inhibitor therapy after tamoxifen, there was no excess increased risk for uterine cancer, the researchers add.
Noting that compliance with the second 5-year tamoxifen schedule was around 80%, the team concludes that full compliance could result in an even greater reduction in breast cancer recurrence.
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