In vivo inhibition of VM with treatment and presence of VM in breast cancer specimens. (a) Vascularity of tumor xenografts in mice was evaluated by factor VIII related antigen staining (brown) for endothelial cells, and Biebrich Scarlet staining (red) for RBCs. (b) Absence of endothelial cells lining the pools of RBCs (vascular channels) was shown by no staining for factor VIII related antigen and positive staining for RBC by Biebrich Scarlet. C) Histological features of the primary human grade 1 breast tumor specimen showing blood vessels positive for CD34 staining (brown) for endothelial cells, and Biebrich Scarlet staining (red) for RBCs. No vascular channels were detected. (d) RBC pooling without the lining of endothelium (vascular channels) in the high-grade invasive ductal breast carcinoma specimen. (e, f) COX-2 staining pattern in grade 1 primary human breast tumor specimen (panel e) and in high-grade invasive ductal carcinoma specimen (penal f). Magnifications are as follows: panels a and b, 100 ×; panels c and d, 200 ×; and panels E and F, 100 × magnification). COX, cyclo-oxygenase; RBC, red blood cell; VM, vasculogenic mimicry.