CD99 (MIC2, p30/32MIC2, HBA-71)

This is a 30-32 kD cell surface glycoprotein encoded by a pseudoautosomal gene located on the X and Y chromosomes. It is expressed by a range of high grade malignancies.

Antibodies are effective on paraffin-embedded tissue5.

Immunohistochemical expression

Positivity takes the form of strong membrane staining.

• normal tissues:

  • cortical thymocytes: medullary thymocytes are usually negative

  • mature peripheral T and B cells are usually negative

  • pancreatic islet cells

  • urothelium

  • some squamous cells

  • columnar epithelial cells

  • fibroblasts

  • endothelial cells2

  • granulosa/Sertoli cells

• T-cell ALL: one T-cell acute lymphoblastic leukaemia6 and seven of 11 T-lymphoblastic lymphomas6. All 8 B-lymphoblastic lymphomas were negative6. Positivity correlates with positivity for TdT7.

• granulocytic sarcoma

• Ewing's sarcoma / PNETs: 13 of 15 Ewing's sarcomas and 14 of 15 PNETS 6

• islet cell tumours

• carcinoids

• small cell carcinoma of lung but not Merkel cell tumours

• rhabdomyosarcoma: 4 of 14 embryonal rhabdomyosarcomas using 12E76 . All 10 alveolar rhabdomyosarcomas were negative6.

• nephroblastoma

• leiomyosarcoma: 6 of 47 cases1

• synovial sarcomas: 41 of 85 cases1

• haemangiopericytomas: 21 of 33 cases1

• malignant fibrous histiocytoma: 9 of 24 cases1

• meningiomas

• Superficial acral fibromyxoma

• solitary fibrous tumours1

• mesenchymal chondrosarcoma

• small cell osteosarcoma

• rarely mesotheliomas: 1 of 10 cases1

• uterine tumours with sex cord differentiation (1/23, 7/74)

• Leydig cell tumour of testis and occasional Sertoli cell tumour of testis

• Sertoli cell tumours of the ovary

• Atypical fibroxanthoma

Diagnostic utility

• Identification of immature lymphocytes in the diagnosis of thymoma

• Diagnosis of precursor T-cell and B-cell lymphoma/leukaemia

• PNET / Ewing's sarcoma

References

1 Ordonez NG. Localized (solitary) fibrous tumor of the pleura. Adv Anat Pathol 2000;7:327-340.

2 Nicholson, S. A., McDermott, M. B., DeYoung, B. R., Swanson, P. E. CD31 immunoreactivity in small round cell tumors. Appl Immunohistochem Molecul Morphol 2000;8:19-24.

3 McCluggage, W. G. Uterine tumours resembling ovarian sex cord tumours: immunohistochemical evidence for true sex cord differentiation Histopathology 1999;34:375-6.

4 Krishnamurthy, S., Jungbluth, A. A., Busam, K. J., Rosai, J. Uterine tumors resembling ovarian sex-cord tumors have an immunophenotype consistent with true sex-cord differentiation. Am J Surg Pathol 1998;22:1078-1082.

5 Leong A S-Y, Cooper K and Leong FJ W-M. Manual of diagnostic antibodies for immunohistology. 2nd edition, 2003

6 Ramani, P., D. Rampling, et al. (1993). "Immunocytochemical study of 12E7 in small round-cell tumours of childhood: an assessment of its sensitivity and specificity." Histopathology 23(6): 557-61.

7 Robertson PB, Neiman RS, Worapongpaiboon S, et al. 013 (CD99) positivity in hematologic proliferations correlates with TdT positivity. Mod Pathol 1997; 10:277-82

©SMUHT/PW Bishop