ACKR1 and cancer: Based on pan-cancer scRNAseq data analysis, Qian et al.12 classified ECs into 5 subtypes: C1_ESM1 for tip cells with high expression of ESM1, C2_ACKR1 for venous ECs with high expression of ACKR1, C3_CA4 in capillary ECs with high expression of CA4, C4_FBLN5 in arterial ECs with high expression of FBLN5, and C5_PROX1 lymphatic ECs with high expression of PROX1.