Flow cytometric immunophenotyping and comparison with immunocytochemistry in small round cell tumors.

OBJECTIVE: To quantitate different antigens by flow cytometric immunophenotyping (FCI) in small round cell tumors (SRCTs) and to compare the FCI technique with immunocytochemistry (IC). STUDY DESIGN: IC and FCI were performed on 24 consecutive cases of SRCT on fine needle aspiration biopsy material using a panel of antibodies-e.g., cytokeratin (CK), leukocyte common antigen (LCA), desmin, epithelial membrane antigen, neuron-specific enolase, chromogranin, retinoblastoma gene product, neuroblastoma clone (NB84a (NB), vimentin and Mic-2 gene product. IC was done by indirect immunoperoxidase and FCI by indirect immunofluorescence on flow cytometry. RESULTS: In Ewing's sarcoma, with the help of FCI, positive results were obtained in an additional 4 samples in CK, 2 samples in actin and 3 samples in desmin. Similarly, one each sample was additional positive regarding Mic-2 and vimentin by IC. In cases of neuroblastoma with the help of FCI, additional positive results were obtained in one each sample of CK, LCA and NB and two in actin. Combined use of FCI and IC helped to show chromogranin positivity in an additional two cases. Divergent differentiation was noted in four cases of Ewing's sarcoma, one neuroblastoma and two peripheral neuroectodermal tumors. CONCLUSION: FCI technique is sensitive, more objective and quantitative in comparison with manual absorbance-based microscopic detection of enzyme immunohistochemistry products. FCI may determine divergent differentiation in SRCTs.