CD99

CD99 is a transmembrane glycoprotein encoded by the MIC2 gene, widely present in lymphocytes, thymocytes, ovarian granulosa cells, testicular Sertoli cells, and other cells. It has various functions such as regulating cell differentiation, mediating cell adhesion, and participating in inflammatory response. In clinical practice, CD99 can serve as a specific diagnostic biomarker for Ewing's sarcoma and primitive neuroectodermal tumor, and it may promote tumor proliferation and metastasis, speculated that CD99 can maintain cancer cell growth by binding to GDF6 or affect cancer cell apoptosis by regulating extracellular vesicle miRNA. Meanwhile, the high CD99 expression in breast cancer suggests that it has tumor promoting effect. It may be because CD99 has two isomers, type I and type II, and type II CD99, which can inhibit the aggregation of homoplastic cells, enhances the invasiveness of cancer cells through some signaling pathway. However, CD99 expression deletion in gastric cancer, cervical cancer, and Hodgkin lymphoma is considered to be related to the occurrence and development of tumors, which may be because it can change the structure of cytoskeleton and the expression of adhesion molecules.