PECAM1 and esophageal squamous cell carcinoma: Furthermore, microvessel density (MVD) was determined by immunohistochemical staining of CD31 in the subcutaneous ESCC tumor xenografts treated with imperatorin or vehicle control, and our results showed that treatment with imperatorin resulted in a significant decrease of MVD, whereas systemic injection of CCL2 via tail vein abolished the suppressive effect of imperatorin on tumor angiogenesis (Figure 4L).