Clinical efficacy of targeted anti-angiogenic therapy is dependent on target molecule expression by tumor blood vessels. Utilizing dual-immunostaining we have demonstrated marked heterogeneity in breast tumor blood vessel expression of the endothelial receptor tyrosine kinase Tie2, phosphorylated Tie2 (pTie2Y1100) and coverage by PDGFR-[beta]-positive pericytes, relative to the pan-endothelial marker CD31. In human breast tumors, the relative proportion of Tie2- and PDGFR-[beta]-positive blood vessels did not correlate to histopathological markers of tumor progression or overall patient survival. In tumors from MMTV-PyVmT transgenic mice, the relative proportion of Tie2-positive vessels was unrelated to tumor grade, while the proportion of pTie2Y1100-positive vessels increased with increasing nuclear grade. These results highlight the need to better understand the factors responsible for Tie2 and PDGFR-[beta] expression by breast tumor endothelial cells and pericytes, respectively, which may aid in enhancing patient selection for targeted anti-angiogenic therapies, and ultimately improve clinical benefit of such therapies.