Purpose-Numerous preclinical studies demonstrate that angiogenesis inhibitors can increase the efficacy of radiation therapy (RT). We sought to examine safety and efficacy of bevacizumab (BV) and RT in soft tissue sarcomas (STS) and explore biomarkers for treatment response.Methods and Materials-Patients (pts) with ≥5 cm, intermediate-or high-grade STS at significant risk of local recurrence (LR) received neoadjuvant BV alone followed by BV plus RT prior to surgical resection. Correlative science studies included analysis of serial blood and tumor samples as well as serial perfusion CT scans.Results-The 20 pts had a median tumor size of 8.25 cm, with 13 extremity, 1 trunk, and 6 retroperitoneal/pelvis tumors. Neoadjuvant treatment was well tolerated with only 4 pts having grade 3 toxicities (hypertension, LFT elevation). BV plus RT resulted in ≥80% pathologic necrosis in 9 of 20 tumors (45%), which is over double the historical rate seen with RT alone. 3 pts had a complete pathologic response. Median microvessel density (MVD) decreased 53% after BV alone (p<0.05), and following combination therapy, median tumor cell proliferation decreased by 73%, apoptosis increased 10.4 fold, and blood flow, blood volume, and permeability surface area decreased by 62-72% (p<0.05). Analysis of gene expression microarrays of untreated tumors identified a 24-gene signature for treatment response. MVD and circulating progenitor cells at baseline and reduction in MVD and plasma soluble c-KIT with BV also correlated with good pathologic response (p<0.05). After a median follow-up of 20 months, only 1 patient had a LR.Conclusions-This exploratory study indicates that BV increases the efficacy of RT against STS and may reduce LR, and thus this regimen warrants further investigation. Gene expression profiles and other tissue and circulating biomarkers show promising correlations with treatment response.