The criteria of the VM structure are as follows: (1) absence of vascular endothelial cells on the inner wall of the VM blood vessel; (2) vascular-like channels are lined with tumor cells; (3) positive for PAS staining but negative for CD31 staining, while the endothelial vascular channels are negative for PAS staining but positive for CD31 staining; (4) erythrocytes in the vascular-like channels [44, 45]. Here, PECAM1 is linked to neoplasm.