Fine-needle aspiration of adult small-round-cell tumors studied with flow cytometry.

Immunophenotypic study is critical for the diagnosis of adult small-round-cell tumors (SRCTs). We describe three patients with Ewing's sarcoma/primitive neuroectodermal tumor (ES/PNET) and one patient with neuroblastoma in which flow cytometry immunophenotyping (FCI) on the fine-needle aspirate (FNA) and bone marrow aspirate (BMA) demonstrated an abnormal population of cells that were CD45(-) and CD16/CD56(+). Four patients with mean age of 30 years, three male and one female, clinically suspicious for a lymphoma or SRCT are described. FNA, BMA, and biopsy specimens were obtained for routine cytologic and histologic evaluation. Fresh tissue was studied by FCI. In all cases, the cytology smears showed small cells with round nuclei, slightly irregular nuclear membranes, fine chromatin, and scant cytoplasm. FCI showed CD16/56(+) and CD45(-) neoplastic cells in all cases. In one case, 76% of these cells were CD99(+). The diagnoses of ES/PNET were confirmed by immunohistochemical, ultrastructural, and cytogenetic studies. ES/PNET in FNA and BMA can be efficiently and rapidly diagnosed by combining cytologic examination with FCI using a panel including CD45, CD16/56, and CD99.