CD 99 (p30/32MIC2)

Dako (12E7), Pharmingen (MIC2) and Signet (013).

All three clones show enhanced immunoreactivity following some method of heat-induced epitope retrieval.

The p30/32MIC2 antigen, also referred to as CD 99 or the MIC2 gene product, is a cell-surface glycoprotein of relative molecular mass of 30 000-32 000 that appears to be involved in cell adhesion processes. It is recognized by a number of monoclonal antibodies including RFB-1, 12E7, HBA71 and 013, although there is some demonstrable difference in sensitivity and perhaps specificity.
CD 99 was first described as a polypeptide expressed in T-cell acute lymphoblastic leukemia and T-ALL derived cell lines, as well as in a subset of cortical thymocytes. It was also found on a group of hematopoietic precursor cells in the human bone marrow including terminal deoxynucleotidyl transferase-positive cells and myelomonocyte progenitors, the expression decreasing with maturation of cells in the latter series. The MIC2 gene has been mapped to the terminal region of the short arm of the X chromosome (Xp22.32-pter) and the euchromatin region of the Y chromosome (Yq11-pter). The gene is expressed in both sexes and escapes X inactivation, making it the first described pseudoautosomal gene in humans (Dracopoli et al, 1985; Fellinger et al, 1991).
The main application of this antigen has been for the differentiation of the group of small round cell tumors in childhood as the marker is strongly expressed in Ewing's sarcoma and the closely related peripheral/primitive neuroectodermal tumors (PNETs). Both show strong membrane and cytoplasmic staining with clones 12E7, HBA71 and 013 (Stevenson et al, 1994; Weidner & Tjoe, 1994; Vartanian et al, 1996). Subsequent studies have also demonstrated positive staining in acute lymphoblastic lymphoma and related leukemias and rhabdomyosarcoma, although to a much lesser degree (Ramani et al, 1993). More recently, immunoreactivity for this marker has been shown in a much wider spectrum of normal tissues and ependymal cells, pancreatic islet cells, urothelium, some squamous cells, columnar epithelial cells, fibroblasts, endothelial cells and granulosa/Sertoli cells. Among the spindle cell neoplastic tissues which show variable positivity for CD 99 are synovial sarcomas, hemangiopericytomas, meningiomas, solitary fibrous tumors and, only very rarely, mesotheliomas. Epithelial tumors expressing CD 99 include neuroendocrine tumors such as islet cell tumors, carcinoid tumors and pulmonary oat cell carcinomas but apparently not Merkel cell carcinomas of the skin (Soslow et al, 1966). Granulocytic sarcomas have been shown to stain for CD 99 (Cooper & Haffajee, 1995).
Positive staining for CD 99 occurs as strong membrane immunolocalization whereas variable heterogeneous staining may be seen in some cases of non-Hodgkin's lymphoma and in occasional Reed-Sternberg cells and their variants.

99 antibodies have proven usefulness for the separation of Ewing's sarcoma and PNETs from the other small round cell tumors in childhood (Pappo et al, 1993; Lumadue et al, 1994) (Appendix 1.3). In addition, this marker can be employed as a diagnostic discriminator for the identification of thymic cortical T cells associated with thymic neoplasms (Chan et al, 1995; Dorfman & Pinkus, 1996) (Appendix 1.11) and in the differential diagnosis of spindle cell tumors. The latter include synovial sarcoma, hemangiopericytoma, meningioma and solitary fibrous tumors, all of which show variable extents of positivity (Renshaw, 1995). The recent demonstration of CD 99 in mesenchymal chondrosarcoma (Granter et al, 1996) emphasizes the need for caution if this marker is to be employed as a diagnostic discriminator for small round cell tumors.

Immunoreactivity is enhanced following heat-induced epitope retrieval. Both 013 and 12E7 have been very effective in our hands but it should be noted that they show different sensitivities, perhaps reflecting different specificities.

•Chan JKC, Tsang WYW, Seneviratne S, Pau MY 1995 The MIC2 antibody 013. Practical application for the study of thymic epithelial tumors. American Journal of Surgical Pathology 19: 1115-1123.

•Cooper K, Haffajee Z 1995 Immunohistochemical assessment of MIC2 gene product in granulocytic sarcoma using six epitope retrieval systems. Applied Immunohistochemistry 3: 198-201.

•Dei Tos AP, Wadden C, Calonje E et al 1995 Immunohistochemical demonstration of glycoprotein p30/32MIC2 (CD99) in synovial carcinoma. Applied Immunohistochemistry 3: 168-173.

•Dorfman DM, Pinkus GS 1996 CD99 (p30/32MIC2) immunoreactivity in the diagnosis of thymic neoplasms and mediastinal lymphoproliferative disorders. A study of paraffin sections using monoclonal antibody 013. Applied Immunohistochemistry 4:34-42.

•Dracopoli NC, Rettig WJ, Albino AP et al 1985. Genes controlling gp25/30 cell-surface molecules map to chromosome X and Y and escape X-inactivation. American Journal of Human Genetics 37: 199-207.

•Fellinger EJ, Garin-Chesa P, Su SL et al 1991. Biochemical and genetic characterization of the HBA71 Ewing's sarcoma cell surface antigen. Cancer Research 51:336-340.

•Granter SR, Renshaw AA, Cletcher CDM et al 1996 CD99 reactivity in mesenchymal chondrosarcoma. Human Pathology 27:1273-1276.

•Lumadue JA, Askin FB, Perlman EJ 1994 MIC2 analysis of small cell carcinoma. American Journal of Clinical Pathology 102:692-694.

•Pappo AS, Douglass EC, Meyer WH et al 1993. Use of HBA71 and anti-b2-microglobulin to distinguish peripheral neuroepithelioma from neuroblastoma. Human Pathology 24:880-885.

•Ramani P, Rampling D, Link M 1993 Immunocytochemical study of 12E7 in small round-cell tumors of childhood: an assessment of its sensitivity and specificity. Histopathology 23: 557-561.

•Renshaw AA 1995 013 (CD99) in spindle cell tumors. Reactivity with hemangiopericytoma, solitary fibrous tumor, synovial sarcoma, and meningioma, but rarely with sarcomatoid mesothelioma. Applied Immunohistochemistry 3: 250-256.

•Soslow RA, Wallace M, Goris J et al 1996. MIC2 gene expression in cutaneous neuroendocrine carcinoma (Merkel cell carcinoma). Applied Immunohistochemistry 4: 235-240.

•Stevenson AJ, Chatten J, Bertoni F, Mittinen M 1994 CD99 (p30/32MIC2) neuroectodermal/Ewing's sarcoma antigen as an immunohistochemical marker. Review of more than 600 tumors and the literature experience. Applied Immunohistochemistry 2: 231-240.

•Vartanian RK, Sudilovsky D, Weidner N 1996 Immunostaining of monoclonal antibody 013 (anti MIC2 gene product) (CD99) in lymphomas. Impact of heatinduced epitope retrieval. Applied Immunohistochemistry 4:43-55. gene product) (CD99) in lymphomas. Impact of heatinduced epitope retrieval. Applied Immunohistochemistry 4:43-55.

•Weidner N, Tjoe J 1994. Immunohistochemical profile of monoclonal antibody 013: antibody that recognizes glycoprotein p30/32MIC2 and is useful in diagnosing Ewing's sarcoma and peripheral neuroepithelioma. American Journal of Surgical Pathology 18: 486-494.

Manual of diagnostic antibodies for immunohistology / Anthony S.-Y. Leong, Kumarasen Cooper, F. Joel W.-M. Leong.