64 year old female with a past medical history of chronic hypertension, type II diabetes mellitus, headache, and hypercholesteremia who presented with pancytopenia of unknown origin. NGS panel was negative for pathogenic mutations. Peripheral blood smears did not show any blasts. ​

Bone marrow biopsy showed hypocellular marrow (5-10%) with mainly small lymphocytes, vasculatures and no significant increase in blasts. There was no significant increase in reticulin fibers 0 out of 3.​

Flow cytometry showed no increase in blasts, there was no increase in blasts by CD34 and CD117 immunohistochemistry stains. ​

Plasma cells, confirmed by CD138 (Image D) were found to stain positive with CD31 (Image C), CD31 also stained vascular endothelial cell as expected. The plasma cells were polyclonal by kappa and lambda stains (not shown).​

CD31 is a member of immunoglobulin superfamily, also known as platelet endothelial cell adhesion molecule (PECAM-1). It is often used as vascular marker. The expression of CD31 plasma cell was rarely reported.  Overall, CD31 can be seen in extramedullary reactive plasma cells, focally in bone marrow reactive plasma cells, and occasionally in extramedullary plasmacytomas (Medina et al., 2002).