The vECs-FLT1 subpopulation represented tumor-associated endothelial cells, which were characterized by high expression level of VEGFR1 (FLT1); moreover, significant number of vECs-FLT1 endothelial cells were found in LC (Figure 6A, Figure S4D). Here, FLT1 is linked to laryngotracheoesophageal cleft.