CD 31 or cluster of differentiation 31, is a blood and intracellularly produced coagulation factor. This is also know as Platelet endothelial cell adhesion molecule or (PECAM-1). CD31 is normally found on endothelial cells, platelets, macrophages and Kupffer cells, granulocytes, T / NK cells, lymphocytes, megakaryocytes, osteoclasts, neutrophils. Because it found on endothelial cells, this makes this a useful tool to identify if a tumour is of vascular origin. This shows a cytoplasmic and membraneous staining pattern as shown below.

Picture 1 – CD 31 positivity in tonsil

CD 31 has several different applications. Below are a few examples.