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Benefits of tamoxifen use continue for years after discontinuation

July 29, 2011

Five years of adjuvant tamoxifen reduces long-term risks of breast cancer recurrence and death, according to a study published this month in The Lancet.  In this meta-analysis, researchers from the Early Breast Cancer Trialists' Collaborative Group (EBCTCG) found that women are a third more likely to survive at least 15 years if they take tamoxifen for several years after their breast cancer surgery.

The researchers conducted a meta-analysis of individual patient data from 20 randomized trials (n=21,457) in early breast cancer of 5 years of daily tamoxifen versus no adjuvant tamoxifen. These women were followed for many years after taking tamoxifen.   In the 10,645 patients with ER-positive disease, receiving 5 years of tamoxifen reduced the recurrence rates throughout the first 10 years (but not after year 10) with a rate ratio (RR) of 0.53 and RR=0.68 for years 0-4 and 5-9, respectively.  This association was independent of progesterone receptor status, age, nodal status, or receipt of chemotherapy.  Furthermore, women who took tamoxifen were also 30 percent less likely to have died of breast cancer 15 years after beginning treatment compared to controls.  Tamoxifen has little or no effect on recurrence or mortality in ER-negative patients. 

This study suggests that the benefits of tamoxifen continue years after the patient has finished the course of treatment.