Sequencing of Tamoxifen and Radiotherapy After Breast-Conserving Surgery in Early-Stage Breast Cancer

Purpose Tamoxifen (TAM) is thought to exert a cytostatic effect on hormone-sensitive breast cancer cells. Some preclinical studies show reduced radiosensitivity in irradiated malignant mammary epithelial cells when pretreated with TAM; other studies refute these results. Recent randomized clinical trials suggest an antagonistic effect of TAM on cytotoxic therapy, with improved disease-free survival (DFS) with sequential versus concurrent TAM. An exploratory analysis was undertaken to evaluate the optimal sequencing of TAM and radiotherapy (RT) after breast-conserving surgery. Patients and Methods Southwest Oncology Group trial 8897 (Intergroup 0102) randomly assigned node-negative women with T1-3 breast cancers to cyclophosphamide, doxorubicin, fluorouracil (CAF); CAF → TAM; cyclophosphamide, methotrexate, fluorouracil (CMF); and CMF → TAM. For this analysis, data are reported only in the TAM groups. RT was allowed either before adjuvant therapy (sequential [SEQ] RT; 107 patients) or after chemotherapy bu...