It is well acknowledged that treatment efficacy could be increased and unnecessary toxicities reduced if a rapid assessment strategy were available to allow individual tailoring of cancer therapy. In this work we focus on using optical tomographic imaging to detect tumor response to anti-angiogenic treatment within the first 5 days of therapy. For this study we used two models with well-characterized and divergent responses to inhibition of vascular endothelial growth factor (VEGF). SK-NEP and NGP cells were implanted intrarenally into NCR nude mice and the resulting tumors were monitored until a threshold of 1-2 g was reached. Optical tomographic imaging with a dual-wavelength (λ = 765nm and 830nm) continuous wave system, was performed prior to the first treatment with the anti-VEGF bevacizumab (BV), as well as 1, 3, and 5 days later. We found that the SK-NEP tumor model, known to be responsive to BV treatment, shows a decrease in hemoglobin levels over the 5 days. Mice implanted with the NGP tumor model, known to be less responsive to treatment, do not show such decreases. These results were further validated with histopathological findings that showed a decrease in tumor vascularization in treated SK-NEP mice. These results suggest that optical tomography is a promising tool for monitoring early tumor response to drug therapy.