['Vascular endothelial growth factor (VEGF) is a mediator of angiogenesis and is up-regulated under hypoxic conditions. Hypoxic tumors are known to exhibit resistance to radiotherapy. We investigated the association between VEGF levels in tumor tissue and the effect of radiotherapy for relapse-free survival (RFS) and overall survival (OS) in node-negative breast cancer.', 'The study was performed on 489 patients; 221 patients received postoperative radiotherapy as part of the breast-conserving therapy (BCT), and 268 patients were treated by mastectomy only. VEGF levels were measured using a quantitative ELISA. None of the patients received adjuvant systemic therapy. The median follow-up was 64 months (range, 2-149) after BCT and 59 months (range, 2-117) after mastectomy. Correlations with well-known prognostic factors were studied, and univariate and multivariate survival analyses were performed.', 'Only in the BCT group, high VEGF levels (equal or above the median level) predicted a reduced RFS and OS in univariate survival analysis (P = 0.004 and P = 0.028, respectively), implying that patients with high VEGF levels have less benefit from BCT. This was seen as a significant interaction between local treatment and VEGF for the total population for RFS (P = 0.012) and OS (P = 0.004). The interaction between local treatment and tumor size was also significant for both RFS (P = 0.046) and OS (P = 0.019) in the multivariate analysis.'] Does vascular endothelial growth factor independently predict the efficacy of postoperative radiotherapy in node-negative breast cancer patients?