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Breast Cancer · Endocrine Therapy · Extended Adjuvant

ATLAS

After completing 5 years of tamoxifen for ER-positive breast cancer, does continuing to 10 years further reduce recurrence and mortality?

Population12,894 women entered the trial; 6,846 had ER-positive disease for breast-cancer outcomes.InterventionContinue tamoxifen to 10 years.ComparatorStop after 5 years.Primary clinical outcomeBreast cancer recurrence and mortality.

Absolute Effect

During years 5–14, recurrence was 21.4% vs 25.1%, an absolute reduction of 3.7 points (NNT ≈ 27). Breast-cancer mortality was 12.2% vs 15.0%, an absolute reduction of 2.8 points (NNT ≈ 36).

Benefit

The benefit was more pronounced after year 10. Breast-cancer mortality rate ratio was 0.71 in the ≥10-year period.

Harm

Endometrial cancer during years 5–14 occurred in 3.1% with continued tamoxifen versus 1.6% after stopping: an absolute increase of 1.5 points, corresponding to an NNH of about 67. Pulmonary embolus incidence was also increased.

Source

Davies C, et al. Lancet. 2013;381:805–816. ATLAS.

Current-practice context · reviewed 14 October 2026

ATLAS established that extending adjuvant tamoxifen to 10 years can reduce recurrence and breast-cancer mortality in ER-positive disease, but duration is individualized today. Consider menopausal status, residual recurrence risk, tolerance, thromboembolism/endometrial risks and whether switching to an aromatase inhibitor is appropriate.

ATLAS primary/long-term report ↗ · Current guideline guidance ↗