Test Details: Immunohistochemical testing is carried out on biopsy/resected tissue specimen. This testing helps to identify specific antigens (proteins) within tissue sections utilizing an antigen-specific antibody. CD31, also known as PECAM-1 (platelet endothelial cell adhesion molecule-1), normally expressed on endothelial cell junctions and on the surface of platelets, monocytes, granulocytes, and B-lymphocytes, is a sensitive and specific marker for blood vessels and vascular tumours.