FLT1 and neoplasm: Angiogenesis-related genes (FLT1, KDR, SPARC, INSR, ANGPT2, and FLT4) and MHC-I molecules (HLA-A, HLA-B, HLA-C, HLA-E, and HLA-F) were highly expressed in cluster 3 ECs, indicating that the cells may function as antigen-presenting cells and promote tumor parenchymal angiogenesis (Figures 6C, E).