PECAM1 and histiocytic sarcoma: Recently, CD31 has been suggested as providing immune privilege to the vascular endothelium.25 Furthermore, in the setting of recovery from myocardial infarction, CD31 can be utilized as a marker for endothelial progenitor cells (EPCs) and capillary density.26 Specifically in HS, previous studies have suggested a mixed vascularization morphology within active lesions related to the presence of a chronic inflammatory stimulus.27 Therefore, the significantly increased levels of CD31+ cells in the HS samples suggest that neovascularization is involved in the HS disease course.