Representative photomicrographs of primary tumor vasculature and examples of tumor emboli within efferent veins. (A) Renal cell carcinoma, (B) hepatocellular carcinoma and (C) follicular thyroid carcinoma. An endothelial layer covering intravascular tumor emboli can be seen using immunostaining with anti-CD31 antibody (AII, BII, CII). The vasculature in the primary tumors of the three carcinomas formed sinusoidal structures surrounding tumor cell nests (anti-CD31 staining, AIII, BIII, CIII). AI, BI and CI are H&E staining. Original magnifications: (AII, BII, CII) ×400, all others ×200.