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Tumor genomic instability and selective treatment pressures result in clonal disease evolution; molecular stratification for molecularly targeted drug administration requires repeated access to tumor DNA. We hypothesized that circulating plasma DNA (cpDNA) in advanced cancer patients is largely derived from tumor, has prognostic utility, and can be utilized for multiplex tumor mutation sequencing when repeat biopsy is not feasible. We utilized the Sequenom MassArray System and OncoCarta panel for somatic mutation profiling. Matched samples, acquired from the same patient but at different time points were evaluated; these comprised formalin-fixed paraffin-embedded (FFPE) archival tumor tissue (primary and/or metastatic) and cpDNA. The feasibility, sensitivity, and specificity of this high-throughput, multiplex mutation detection approach was tested utilizing specimens acquired from 105 patients with solid tumors referred for participation in Phase I trials of molecularly targeted drugs. The median cpDNA concentration was 17 ng/ml (range: 0.5-1600); this was 3-fold higher than in healthy volunteers. Moreover, higher cpDNA concentrations associated with worse overall survival; there was an overall survival (OS) hazard ratio of 2.4 (95% CI 1.4, 4.2) for each 10-fold increase in cpDNA concentration and in multivariate analyses, cpDNA concentration, albumin, and performance status remained independent predictors of OS. These data suggest that plasma DNA in these cancer patients is largely derived from tumor. We also observed high detection concordance for critical 'hot-spot' mutations (KRAS, BRAF, PIK3CA) in matched cpDNA and archival tumor tissue, and important differences between archival tumor and cpDNA. This multiplex sequencing assay can be utilized to detect somatic mutations from plasma in advanced cancer patients, when safe repeat tumor biopsy is not feasible and genomic analysis of archival tumor is deemed insufficient. Overall, circulating nucleic acid biomarker studies have clinically important multi-purpose utility in advanced cancer patients and further studies to pursue their incorporation into the standard of care are warranted.

2530 Background: GL-ONC1 is a genetically engineered vaccinia virus attenuated by insertion of the RUC-GFP (Renilla luciferase and Aequorea green fluorescent protein fusion gene), beta-galactosidase (lacZ) and beta-glucuronidase (gusA) reporter genes into the F14.5L, J2R (thymidine kinase) and A56R (hemaglutinin) loci. A phase I clinical trial of iv GL-ONC1 was pursued to evaluate safety, tolerability, tumour delivery, neutralizing antibody development and anti-tumour activity. Methods: GL-ONC1 was administered to patients with advanced solid tumours at escalating doses (1×105, 1×106, 1×107, 1×108, 1×109, 3×109 plaque-forming units (pfu) on day 1; 1.667×107 and 1.667×108 pfu on day 1-3 of a 28-day cycle) using a 3+3 dose escalation design. Green fluorescent protein (GFP) imaging was performed on skin rash and mucosal tumour lesions at baseline and after each cycle. Optional tumour biopsies were obtained for pharmacodynamic and viral delivery evaluation. Results: 27 patients (21 males, median age 60 years) were treated. One of six patients at the 1x109 pfu dose level developed a dose-limiting, grade 3 rise in aspartate transaminase levels after a single infusion. Other reported adverse events (grade 1/2) included pyrexia (21), musculoskeletal pain (9), fatigue (8), nausea (7), and vomiting (4). Two patients developed skin rash during the first week of treatment, which appeared green by GFP and were positive to viral plaque assay (VPA). VPA of blood, urine, stool and sputum were negative for viral shedding in all but one patient who had positive shedding for 11 days. Increased neutralizing antibody titres were detected in all tested patients apart from one. Best response by RECIST was stable disease at 48 weeks (1), 24 weeks (3) and 8-12 weeks (5). A patient with squamous cell carcinoma of the tongue had a biopsy after 4 cycles which showed positive IHC staining of vaccinia virus. This is the first time that a virus is shown to be delivered to solid tumour after iv delivery. Conclusions: GL-ONC1 administered iv is well tolerated, with documented colonisation in patient tumour, and preliminary evidence of anti-tumour activity.