COL18A1 and neoplasm: Examination of cluster-specific marker genes showed that tumor ECs expressed a unique set of genes such as Col18a1 and Aplnr, but also shared a number of expressed genes with venous ECs, especially with PV, such as Cd63, Ehd4, and Cd200 (Fig. 2c and d, Supplementary Fig. 3a, and Supplementary Table 2).