Purpose To assess the impact of sequencing of tamoxifen and radiation therapy (RT) on outcomes in early-stage breast cancer. Patients and Methods This retrospective study evaluates the effect of the sequence of tamoxifen with RT on outcomes in stage I to II breast cancer patients who underwent breast-conservation treatment (BCT) and received adjuvant tamoxifen, with or without adjuvant chemotherapy. Patients were grouped as concurrent (tamoxifen given during RT followed by continued tamoxifen; 174 patients) and sequential (RT followed by tamoxifen; 104 patients). Results Median follow-up after RT was 8.6 years for both groups. The pathologic T and N stage, race, estrogen and progesterone status, number of positive nodes, and RT were comparable between the two groups (all P ≥ .08). More women age 49 years or younger and women who received chemotherapy were in the sequential group than the concurrent group (6% and 25%, respectively; P < .0001). The sequence of tamoxifen therapy did not influence 10-year local recurrence rates (sequential, 7%; concurrent, 3%; P = .52), overall survival (sequential, 86%; concurrent, 81%; P = .64), or relapse-free survival (sequential, 76%; concurrent, 85%; P = .35). When adjusting age and chemotherapy use in the multivariable Cox model, hazard ratios comparing sequential versus concurrent tamoxifen therapy were 1.56 (95% CI, 0.87 to 2.79), 1.23 (95% CI, 0.63 to 2.41), and 1.22 (95% CI, 0.33 to 4.49) for the overall survival, relapse-free survival, and local recurrence, respectively. Conclusion The therapeutic regimens of tamoxifen given concurrently or sequentially with RT both appear to be reasonable options for patients treated with BCT.
