CD31 is one of the most frequently utilized immunohistochemical markers for endothelial cells, for example, as a marker of angiogenesis in the settings of atherosclerosis and abdominal aortic aneurysm [21], for the quantitative analysis of blood vessels [22], and for determining the degree of neovascularization in a variety of neoplasms, including cervical cancer, ovarian cancer, and Kaposi sarcoma [22, 23, 24]. Here, PECAM1 is linked to Kaposi's sarcoma.