SLC6A4 and neoplasm: These subclusters were characterized based on highly expressed marker genes: Endo-C1 as extra-alveolar capillary ECs (SLC6A4 + FCN3 + EDN1 +), Endo-C2 as alveolar capillary ECs (HPGD + EDNRB + IL1RL1 +), Endo-C3 as tumor-associated ECs (PLVAP + SPRY1 + HSPG2 +), Endo-C4 as arterial ECs (GJA5 + FBLN5 +) and Endo-C5 as lymphatic ECs (CCL21 + TFF3 +) (Figs. 9B and S17B).