SLC6A4 and lung adenocarcinoma: A recent study reported that PECs in human lung adenocarcinomas consist of multiple subtypes: extra-alveolar capillary ECs divided into two subclusters based on SLC6A4+ and C-C Motif Chemokine Ligand 2 positive (CCL2+) expression, and tumor ECs also divided into two subclusters via SLC6A4+ and CCL2+ expression, including tip ECs and high endothelial venules (HEVs).