CD99 by IHC-12376 - Technical only, 12379 - Technical & interpretation

Test info

CD99 by IHC
12376 - Technical only, 12379 - Technical & interpretation

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


AHL - Immunohistochemistry
Mo - Fr
1 - 2 days

Immunohistochemical staining and microscopic examination

Clinical and Interpretive info


If requested, an interpretive report will be provided



  • 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

Strong reactivity Variable reactivity Focal reactivity
Adenohypophysis Endothelial cells Stomach (chief cells)
Ependymal cells Fibroblasts Bone marrow (rare lymphocytes)
Pancreatic islet cells Smooth muscle Lymph node (rare lymphocytes)
Granulosa cells Skeletal muscle Spleen (rare lymphocytes)
Sertoli's cells Columnar epithelium Kidney (collecting ducts and distal convoluted tubules)
Cortical thymocytes Squamous epithelium  
Hassal's corpuscles    
Myenteric plexus    
Hepatocytes (fetal not adult)    

CD99 Reactivity in tumors

95-100% Ewing's Sarcoma
95-100% PNET Peripheral Neuroepithelioma
Rare Rhabdomyosarcoma
up to 90% Lymphoblastic lymphoma

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


  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.


88342 - 1st stain
88341 - each additional stain