Comparative analysis of electron microscopy and immunocytochemistry in the cytologic diagnosis of malignant small round cell tumors.

OBJECTIVE

To compare the contributions of electron microscopy (EM) and immunocytochemistry (ICC) as adjuncts in the cytodiagnosis of malignant small round cell tumors (MSRCT).

STUDY DESIGN

This prospective study included 57 cases with a preliminary aspiration diagnosis of MSRCT. The contributions of EM and ICC in arriving at a specific diagnosis were evaluated.

RESULTS

The 57 cases included 22 cases of Ewing's sarcoma/peripheral neuroectodermal tumor (PNET), 12 neuroblastomas, 8 Wilms' tumors, 6 rhabdomyosarcomas, 5 lymphomas, 2 retinoblastomas and 1 synovial sarcoma. One case remained unclassified. Electron microscopy was crucial to the diagnosis in 38.4% cases as against 39.2% of cases by ICC. The light microscopic diagnosis was confirmed in 42.3% and 53.5% cases by EM and ICC, respectively. EM and ICC were inconclusive for a specific diagnosis in 19.2% and 7.1% of cases, respectively. Technically unsatisfactory preparations in EM and ICC accounted for 5 and 1 cases, respectively. The overall efficiency in making a diagnosis was 80.7% for EM versus 92.8% for ICC. Aberrant expression of antigens led to difficulties in interpretation of ICC, and EM was particularly helpful. The ultrastructural demonstration of neural differentiation in Ewing's sarcoma/PNET tumors helped place tumors in the PNET category.

CONCLUSION

While ICC is the ancillary method of choice in the cytologic diagnosis of MSRCT, EM contributes to the diagnosis and improves diagnostic accuracy.