VWF and neoplasm: Although these microfluidic tubes remain elusive, they may be defined as follow: (i) absence of endothelial markers (CD34, CD31, von Willebrand factor vWF) on the inner wall, (ii) vascular-like channels are lined with tumor cells; (iii) positive for PAS (periodic acid–Schiff) staining, and (iv) presence of erythrocytes in their lumen [110,111].