Yu NY, Iftimi A, Yau C, et al. - In this secondary analysis of patients from the Stockholm Tamoxifen (STO-3) trial, researchers examined postmenopausal patients with lymph node-negative breast cancer who were randomized to receive adjuvant tamoxifen or no endocrine therapy to assess long-term survival with tamoxifen treatment for patients with luminal A or luminal B tumor subtype. Using the Swedish National registers, they extracted complete long-term observation data up to the completion of the STO-3 trial on December 31, 2012. Long-term risk of distant metastatic disease, which was attenuated with tamoxifen therapy, was seen in patients with luminal A subtype tumors. In contrast, an early risk of distant metastatic disease was found in patients with luminal B tumors and a reduction in tamoxifen benefit over time was noted in these patients.