Vascular localization and expression of endothelial molecules at the protein level in B16.F10 tumors growing at three different stages of tumor growth. Expression of VCAM-1 and ICAM-1 was highest in the early-stage tumors, as compared to intermediate and large tumors. A granular pattern of vWF expression was found in a small number of tumor vessels; the majority of them were negative for vWF. Tie2 expression remained the same throughout tumor development and was observed in only a subset of the vessels. The top three and bottom three rows of panels represent immunohistochemical staining of consecutive sections. Arrowheads point to the structures that are enlarged in the insets. Thin arrows point to vessels in the large tumor that are positive for Tie2, while the largest vessel in the same photograph did not express detectable levels of Tie2 protein. Pictures are representative examples of each experimental group (Magnification 100x).