VEGF 

Try to read this paper =D 

http://www.sciencedirect.com/science/article/pii/S0002944010641545

What do you want to look at? Do you want to quantify the angiogenesis response? Do quantitative immunohistochemistry (IHC) with a specific marker for blood vessels (there are many, e.g. PECAM-1, CD45, SMA depending on your questions). VEGF is indirect and even a high expression of VEGF might not result in angiogenesis if it is captured/sequestered/degraded/etc. And you can have robust angiogenesis without VEGF. Don't measure the cause, but measure the effect. In some conditions, e.g. diabetes, the response to VEGF is blunted. However, quantitative IHC is quite difficult to do right (but if you have large differences, you shouldn't have any problems). If you can see the difference through the microscope, you will be able to measure it.

Receptor tyrosine kinase Tie2 and the corresponding ligand Angiopoietin are related to the immature structure of neovasculature of tumor tissues.Tie2 is specifically expressed in endothelial cells, which is a reliable marker to identify the angiogenesis. Further, Prox1 is a master transcription regulator in the new formation of lymph vessels in association with VEGF-C/D. That is why you have to check the Prox1 expression status to distinguish between the formation of blood vessels and lymphatic vessels.

Yes, the Tie2 receptor is also a possible marker. If you use Tie2 (or Tie1 for that matter), just make sure not to measure blood cells (some lines of hematopoietic cells do express them). The staining patterns will be different though, you'll easily see if you have such pattern of individual cells as opposed to a network. But if they are interspersed with your vessels, automatic quantitation might be challenging. And of course, you might not be interested in lymphatic vessels (since you asked specifically about angiogenesis and not lymphangiogenesis).

Collagenase-1 (C1) and oncofetal fragment of fibronectin (Fn-f) may also a usefull markers. Moreover,  circulating endothelial cells (CECs) and circulating endothelial progenitor cells (CEPs) may act as a surrogate marker for pathological angiogenesis.

Michael  you touch the point. I have CD31(PECAM-1) and VEGF IHC data, I can see the differences but is hard to do a quantitative analysis in a accurate manner. Thanks for all the suggestions! And let's keep the discussion open.....

Try CD 105 (Endoglin). Supposed to be more reliable for evaluating tumor angiogenesis.