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Continuation of tamoxifen beyond standard 5 years reduces breast cancer recurrence, preliminary data show

Tuesday, December 18 2007 | Comments
Evidence Grade 0 What's This?
Continuation of tamoxifen beyond the current standard duration of 5 years reduces recurrence over the next few years, according to an early analysis of the latest preliminary data from the ATLAS study.

The researchers explained that despite data showing that 5 years of tamoxifen therapy substantially reduces the annual recurrence rate in estrogen receptor (ER)-positive early breast cancer throughout the first decade (0-9 years), the annual recurrence rate for ER-positive disease remains "comparatively high" for up to 14 years after treatment, and perhaps beyond that.

To evaluate how 10 years of tamoxifen therapy compares with the standard duration of 5 years, the researchers randomized 11,500 women with early breast cancer (59% ER-positive; 41% ER untested) who had completed 5 years of adjuvant tamoxifen therapy to continue tamoxifen for another 5 years or to stop such therapy (control arm). Patients' compliance, hospital admission(s), breast cancer recurrence (including new contralateral disease), incidence of other new primary cancer, death, and cause of death were recorded during annual follow-up.

The mean follow-up after randomization was 4.2 years, which represented approximately 48,000 woman-years of follow-up. During this period, the annual recurrence rate in each of the 2 treatment groups was approximately constant during and after the 5-year trial treatment period (i.e., years 5-9 and years 10-14 after first starting tamoxifen). Of the 1,500 reported recurrences, 1,353 occurred during years 5-9 as compared with the approximately 211 that occurred in years 10-14, according to these preliminary data.

The overall recurrence rate was significantly lower among those in the 10-year tamoxifen arm as compared with those in the control group. No significant heterogeneity was seen in this recurrence rate reduction with respect to ER status, time period (years 5-9 or 10-14), age, or nodal status (at time of diagnosis).

Approximately 1,200 deaths were reported, with around 700 after recurrence (mostly from breast cancer) and approximately 500 before recurrence (all from other causes).

Breast cancer mortality and overall mortality were lower in the 10-year group than in the control group, but the differences in these rates did not reach statistical significance.

"This large study shows that continuation of tamoxifen beyond the first 5 years reduces recurrence over the next few years, but further follow-up is needed to assess reliably the longer-term effects on recurrence and the net effects, if any, on mortality," the researchers concluded. (Peto R, et al. Abstract 48.)

This information concerns a use that has not been approved by the Food and Drug Administration.

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