Vascular endothelial growth factor (VEGF) plays a central role in tumor growth, metastasis and angiogenesis. Various drugs (such as Avastin (R)) interfere tumor growth at this pathway. CellTrend were the first to describe auto-antibodies against VEGF and measures them with an validated ELISA. This discovery enables new strategies for personalization of tumor therapy and may possibly lead to stratification of patients in responders and non-responders prior to therapy.