Hematopoietic system stem cells exhibit CD31 expression, which is mainly employed to pinpoint and gather these cells for research investigations and bone marrow transplants. Since endothelial cells also demonstrate this marker, CD31 antibodies have been utilized to determine the vascular beginnings of neoplasms. 1-3 Vascular endothelial cells have been shown to be highly specifically and sensitively targeted by anti-CD31. 4 There has been no staining seen in nonvascular tumors (except for hematopoietic neoplasms).