PECAM1 and neoplasm: Meanwhile, we used sections of xenograft tumors in the following determinations: in vivo cell proliferation status by proliferating cell nuclear antigen (PCNA) immunohistochemical staining (Figure 10B), microvessel density (MVD) by CD31 staining (Figure 10C), and tumor cell apoptosis by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay (Figure 10D).