Histology & Molecular Genetics: ...................................................................... ETB/EOE (classical Ewing's): Round to oval nuclei with fine dispersed chromatin without nucleoli. Occasionally, cells with smaller, more hyperchromatic (?degenerative) nuclei are present giving a "light cell-dark cell" pattern. The cytoplasm is variable, but in the classic case it is clear & contains glycogen. Glycogen can be highlighted with a periodic acid-Schiff (PAS) stain. The tumor cells are tightly packed & grow in a diffuse pattern without evidence of structural organization. Many pathologists do not make a distinction between EOE and PNET. PNET: Round to ovoid hyperchromatic cells with minimal cytoplasm. The cells are arranged in nests & trabeculae with variable rosette formation. The rosettes may have a central lumen, but are often ill-defined. They are composed of tumor cells arranged around an empty space. The classic lobular growth pattern is best seen at low power, This is different from the typical diffuse growth seen in classical Ewing's. ---Variable staining with neural markers: neuron-specific enolase, Leu-7, synaptophysin, neurofilament, & S100 ...................................................................... The MIC2 gene product (CD99) is a surface membrane protein that is expressed in most cases of Ewing's sarcoma/PNET family of tumors. It is useful in the diagnosis of these tumors when the results are interpreted in the context of clinical & pathologic parameters How to Distinguish PNET & Ewing’s from other small round cell tumors? The monoclonal antibody, HBA71, recognizes a cell-surface glycoprotein (p30/32MIC2) in human Ewing’s sarcoma & PNET. The strong immunoreactivity of HBA71 in Ewing’s sarcoma & PNET distinguishes these tumors from other small round cell tumors of childhood & adolescence. Cytogenetics: EWS locus on chromosome 22 band q12
TREATMENT CHEMOTHERAPY: 1. VACA regimen (vincristine, actinomycin D [dactinomycin], cyclophosphamide, and Adriamycin [doxorubicin] 2. VAdriaC alternating with ifosfamide & etoposide 3. CyVADIC - 2 Cyclophosphamide 600 mg/m2 IVB day 1 Vincristine 1.4 mg/m2 IVB* weekly X 6 then 1.4 mg/m2 IVB* day 1 each cycle Doxorubicin 15 mg/m2 CIV days 1-4 Dacarbazine 250 mg/m2 CIV days 1-4 OR Doxorubicin 22.5 mg/m2 CIV days 1-4 Dacarbazine 225 mg/m2 CIV days 1-4 Repeat cycle every 21 to 28 days for 18 months. *Maximum vincristine dose is 2 mg. At total doxorubicin dose (450 mg/m2), substitute dactinomycin 2 mg/m2 on day 1 of each cycle. Ref: Benjamin RS: In RT Skeel (ed):Handbook of Chemotherapy, Boston, Little Brown, p 203 (1987).
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