CD99 is a transmembrane glycoprotein, also known as MIC2. It is involved in T-cell adhesion, leukocyte migration and differentiation of primitive neuroectodermal cell. CD99 labels lymphocyte, ovarian granulosa cells, pancreatic islet cells, sertoli cells, CNS ependymal cells and endothelial cells. CD99 has been useful in diagnosis of Ewing's sarcoma, sex cord-stromal tumor, and endocrine tumor of pancreas. Additionally, it is found in a subset of other tumors including lymphoblastic lymphoma, breast carcinoma and other malignancies.