PECAM1 and neoplasm: To further corroborate the likely presence of pericytes within the tumor vasculature, we stained Eml4-Alk and healthy lungs for CD31 and a second pericyte marker, the muscular intermediate filament desmin31, and observed desmin-positive cells surrounding CD31-positive endothelial cells within Eml4-Alk tumors but not in NAT (Fig. S11b) nor healthy tissue (Fig. S11d).