PECAM1 and neoplasm: Immunohistochemical (IHC) staining in the viable region revealed that, at 4 days after treatment, IRE induced a transient increase in microvessel density (MVD) in the viable tumor region (7.1 ± 0.5% CD31+ pixels per 200× visual field, mean ± SEM, n = 10–15) compared to untreated controls (2.0 ± 0.3%, Fig. 6b).