Ultrastructure of the primitive neuroectodermal tumors (PNET)

We report a prospective series of consecutive cases of primitive neuroectodermal tumor (PNET) studied by electron microscopy. Virtually all specimens showed a differentiation along neuroblastic lines as evidenced by the presence of neurites, dense-cored vesicles, microtubules and adhesive plaque junctions. We observed also numerous intracytoplasmic cilia and autophagic vacuoles. Synaptic specializations were only rarely seen. We conclude that PNET is a tumor category which is not undifferentiated ("primitive") and clearly exhibits features of neuroblastic differentiation.