- Tamoxifen therapy is associated with a 15-year benefit in luminal A breast cancer, whereas its benefit is shorter, at 5 years, for luminal B tumors.
Why this matters
- Risk for distant metastasis persisted for 25 years postdiagnosis with luminal A tumors but attenuated at 5 years for luminal B disease.
- Secondary analysis of the Stockholm Tamoxifen (STO-3) trial (originally 1976-1990) conducted at 25 years in postmenopausal patients with estrogen receptor (ER)-positive, node-negative breast cancer.
- Tamoxifen (vs no tamoxifen) was randomly assigned to patients for ≥2 years; patients who were recurrence-free were further randomly assigned to 3 more years of tamoxifen vs no tamoxifen.
- Primary outcome was distant recurrence-free interval.
- Funding: Swedish Research Council; others.
- Luminal A group (183 treated, 153 untreated): patients benefited for 15 years postdiagnosis (HR, 0.57; 95% CI, 0.35-0.94) but remained at risk for distant metastasis throughout the 25-year follow-up.
- Luminal B group (64 treated, 62 untreated): patients benefited for 5 years (HR, 0.38; 95% CI, 0.24-0.59), at which point the risk for distant metastasis attenuated.
- Duration of tamoxifen treatment unreported.
- Treatments have changed since trial start.