Contribution of electron microscopy of cell cultures to the classification of three round cell sarcomas in children

We have studied three round cell sarcomas from pediatric patients in tissue culture to compare the electron microscopic morphology of cells in culture to cells from original biopsy specimens. None of the original tumors displayed distinctive features by light microscopy that would allow classification of a specific tumor type, and electron microscopy was not helpful in identifying specific morphologic features that would allow further classification of tumor types. However, electron microscopy of cells in culture from the three neoplasms revealed distinctive morphologic features that did allow further classification of all three tumors. Cells from an inguinal lymph node, which were cultured in soft agar tumor colony-forming assay, revealed Z-bands and actin and myosin filaments indicative of a rhabdomyosarcomatous nature for the tumor. Cells from 5-day, 10-day, and 4-month cultures of a bone marrow metastasis of a second tumor revealed features of skeletal muscle in the young cultures and neuroblasts in the older culture, suggesting a primitive neuroectodermal neoplasm. Cultured cells from the third tumor, a neoplasm of the calf in an infant, displayed large lakes of glycogen, typical of cells of Ewing's sarcoma, which were not present in the cells examined from the original lesion. Ultrastructural studies of cells in culture have the potential to add morphologic data that may be useful to further define and classify a neoplasm, as illustrated in the 3 cases reported here.