For patients with stage IV colorectal cancer, resection of the asymptomatic primary tumor provides only minimal palliative benefit, can give rise to major morbidity and mortality and therefore potentially delays beneficial systemic chemotherapy. When presenting with asymptomatic disease, initial chemotherapy should be started and resection of the primary tumor should be reserved for the small portion of patients who develop major complications from the primary tumor.

Vascular endothelial growth factor‐A (VEGF‐A) is one of the most important angiogenic factors. Here, we studied in a nude mouse model whether the expression of VEGF‐A in a tumor could be imaged with a radiolabeled anti‐VEGF antibody. The humanized anti‐VEGF‐A antibody A.4.6.1. (bevacizumab), which is reactive with all VEGF‐A isoforms, was radiolabeled with In‐111 or with I‐125. The accumulation of the radiolabeled antibodies in VEGF‐A expressing tumors (LS174T) in nude mice was examined in biodistribution studies and by gamma camera imaging. The uptake of the In‐111‐bevacizumab in the tumor at 3 days p.i. was significantly higher than that of I‐125‐bevacizumab (19.4 ± 7.0 %ID/g vs. 9.6 ± 3.3 %ID/g, p = 0.04). Coinjection of an excess unlabeled antibody resulted in a significant decrease in radioactivity concentration in the tumor (<2.9 ± 1.9 %ID/g, p < 0.005), indicating VEGF‐mediated antibody uptake. Highest uptake in the tumor was observed at relatively low antibody protein doses (<3 μg) (20–25 %ID/g). VEGF‐A‐expressing tumors could be clearly visualized on planar scintigraphic images from 24‐hr post injection onwards. In conclusion, VEGF‐A expression in tumors can be visualized specifically with radiolabeled anti‐VEGF‐A‐mAb. © 2008 Wiley‐Liss, Inc.

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