BMC Cancer 2008, 8:352 http://www.biomedcentral.com/1471-2407/8/352 from control-treated animals were on average over 1 g in size whereas Pan02 tumors from control-treated animals were on average just over 0.4 g in size. Thus it is possible that the xenograft tumors are more dependent upon VEGF-induced angiogenesis than the Pan02 tumors and thus anti-VEGF strategies are more effective as standalone agents in this setting. We also observed in both tumor models that CT-322 as a single agent reduced microvessel density. Interestingly, Pan02 tumors from mice treated with CT-322 and gemcit- abine did not show the same degree of reduction in microvessel density as tumors from mice treated with CT- 322 alone. This is perplexing considering that the combi- nation therapy was more effective at reducing overall tumor size. One possible explanation is that not all the blood vessels stained with MECA-32 are functional. In future studies this could determined by intravenous injec- tion of an endothelial cell marker (eg., tomato lectin) or a fluorescent dye to track perfusion. An alternative non- exclusive explanation is that a high percentage of the blood vessels present in the tumors in the combination treated group have been co-opted from normal pancreas and are associated with pericytes and thus less sensitive to anti-VEGF therapy. This is plausible given that the size of the tumors is quite small in the combination treated group. It is worth pointing out that the tumor weights shown in figures 3 and 4 include residual normal pan- creas, which typically weighs 0.1–0.15 g. It is difficult especially in the Pan02 model to dissect the tumor from the normal tissue due to the local invasion by the tumor. Thus, especially in the syngeneic model we may be under- estimating the efficacy of CT-322-based therapy. CT-322 has begun clinical trials and initial results from the first phase I studies were discussed recently at the 2008 American Society of Clinical Oncology meeting [24]. Thirty nine patients with solid tumors or non-Hodgkin's lymphoma were enrolled. 2 mg/kg/week was determined to be the maximum tolerated dose and out of 37 patients evaluated 49% had stable disease. These are promising results and have prompted a phase II study in combina- tion with irinotecan in patients with recurrent glioblast- ome multiforme [24]. Conclusion Our results show that in two aggressive preclinical pancre- atic cancer models, the strategy of selectively targeting VEGFR2 with CT-322 is effective. This compound is exper- imentally useful in that it blocks both mouse and human VEGFR2, thus allowing us to demonstrate the effective- ness of this drug in a fully immunocompetent mouse model. We also show that CT-322 enhances the efficacy of gemcitabine in this setting. As gemcitabine typically only prolongs life by a few months, agents improving its effi- cacy are needed. Further, these data demonstrate the safety and therapeutic utility of the Adnectin platform and suggest that further investigation of CT-322 is warranted in both animal models and clinical trials. Abbreviations VEGF: Vascular endothelial growth factor; VEGFR1: VEGF receptor 1; VEGFR2: VEGF receptor 2; TCI: Tumor cell injection; PBS: Phosphate buffered saline; i.p. : Intraperi- toneal; H&E: Hematoxylin and eosin. Competing interests This study was supported in part by a sponsored research agreement from Adnexus to RA Brekken. Furthermore, R Mamluk and H Wong were full time employees at Adn- exus at time of these studies. Grant Support This work was supported in part by the Effie Marie Cain Scholarship, a sponsored research agreement from Adn- exus to RAB and a postdoctoral fellowship from the Susan G. Komen Foundation to SPD. Authors' contributions SPD helped design some of the experiments, performed therapy studies, analyzed the data, and drafted the manu- script. LAS performed immunohistochemical analysis of tumor tissue, analyzed data, and participated in drafting the manuscript. AWB initiated the in vivo studies and helped design the experiments. AFM and JGC provided technical assistance throughout the study including all of the animal experiments and subsequent tissue analysis. RM conceived the study, provided material, assisted in the study design, and interpretation of the data. HW provided material, assisted in the interpretation of the data, and contributed to the drafting of the manuscript. RAB super- vised and coordinated the study, finalized the manuscript, and obtained the funding to perform the studies. All authors read and approved the final manuscript. Acknowledgements We gratefully acknowledge the support and critique of this work from Drs. 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