All IHC stains will include a positive control tissue

• O13 (CD99) detects a cell surface antigen which is expressed almost exclusively on the cell membrane of Ewing's sarcoma and PNET (Primitive Neuroectodermal Tumor) but not on other small blue cell tumors (see below)
• O13 (CD99) can be useful in a panel of Immunostains for resolution of diagnostic difficulties in small blue cell tumors of childhood
• 95-100% of Ewing's sarcomas and PNETs will show positive staining for O13 (CD99)
• One must utilize O13 (CD99) in a panel as it is expressed in a wide variety of neoplasms
• Most small blue cell tumors are negative for O13 (CD99) with the exception of Acute Lymphocytic leukemia/Lymphoma. In addition, occasional rhabdomyosarcomas, Wilm's tumors and small cell osteosarcomas will show heterogeneous staining for O13 (CD99). When using a panel approach 013 can be a useful adjunct to diagnosis
• Rhabdomyosarcomas will usually express Muscle Specific Actin and desmin which Ewing's/PNET will not
• In some cases, cytogenetics may be helpful. Ewing's sarcoma and PNET usually (>90%) will show a characteristic cytogenetic abnormality t(11;22)(q24:q12)
• Reactivity of the antigen which O13 (CD99) is directed against, is maintained in decalcified tissue.²
• Up to 60% of monophasic synovial sarcomas can be O13 (CD99) positive ⁴, so this can be a diagnostic pitfall

Submit a formalin-fixed, paraffin-embedded tissue

Formalin-fixed, paraffin-embedded (FFPE) tissue block

FFPE tissue section mounted on a charged, unstained slide

Ambient (preferred)

• Unlabeled/mislabeled block
• Insufficient tissue
• Slides broken beyond repair

Immunohistochemical staining and microscopic examination

If requested, an interpretive report will be provided

Specifications

• O13 (CD99) detects the HBA71 antigen. HBA71 antigen is a cell surface glycoprotein (p30/32 MIC2) which is encoded by the MIC2 gene on chromosomes X and Y
• O13 (CD99) is not the only antibody which recognizes the HBA71 molecule. Others are 12E7, RFB-1 and the original antibody by the same name HBA71. These all recognize different epitopes on the same molecule. O13 (CD99) and HBA71 are most frequently used in the current literature
• Significance of O13 staining is not known

Staining pattern

• Cell membrane is typical. Cytoplasmic and perinuclear has been described

O13 (CD99) Immunoreactivity in Normal Tissue

CD99 Reactivity in tumors

CD99 has also been reported in:

• Alveolar Soft Parts Sarcoma
• Astrocytoma
• Embryonal carcinoma
• Ependymoma
• Glioblastoma
• Granulosa cell tumor
• Hemangiopericytoma
• Immature teratoma
• Islet cell tumor of pancreas (G+, PP+, CGA+)
• Malignant Fibrous Histiocytoma
• Melanoma
• Meningioma
• Neuroendocrine Carcinoma (carcinoids and small cell carcinoma)
• Serous Cystadenocarcinoma
• Solitary Fibrous tumor
• Squamous cell carcinoma
• Synovial Sarcoma
• Uterine Sarcoma

References

1. Stevenson, AJ, Chatten J, Bertoni F and Miettinen M.; CD99 (p30/32 MIC2) Neuroectodermal/Ewing's Sarcoma Antigen as an Immunohistochemical Marker; Applied Immunohistochemistry; 2(4):231-240, 1994.
2. Fellinger EJ, Garin-Chesa P, Glasser DB, Huvos AG, Rettig WJ.; Comparison of Cell Surface Antigen HBA71 (p30/32 MIC2), Neuron-Specific Enolase and Vimentin in the Immunohistochemical analysis of Ewing's Sarcoma of Bone; American Journal of Surgical Pathology; 16(*):746-755, 1992.
3. Dehner LP; Primitive Neuroectodermal Tumor and Ewing's Sarcoma; American Journal of Surgical Pathology; 17(1):1-13, 1993.
4. Dei Tos et. al., Immunohistochemical Demonstration of Glycoprotein P30/32MIC2(CD99) in synovial sarcoma; Applied Immunohistochemistry; 3(3):168-173, 1995.