Ultrastructural diagnosis of large cell 'undifferentiated' neoplasia.

Large cell undifferentiated neoplasia' provides a generic designation for a heterogeneous group of neoplasms which by histological study, are devoid of discriminate architecture and appear under the light microscope as patternless sheets of large cytoplasmic cells. The interpretation of such a tumour will routinely present significant problems in differential diagnosis. By conventional light microscopy the neoplasm may subjectively be judged to represent a certain form of carcinoma or large cell lymphoma, but often identification is relegated to a label of "consistent with', or "undifferentiated malignant neoplasm'. Such interpretations are not acceptable and preclude rational management decisions. This paper has analysed tumour cell ultrastructure derived from a spectrum of clinicopathological situations involving the diagnostic problem of the large cell undifferentiated neoplasm. The fine structural morphologies of these enigmatic tumours are often sufficiently specific to allow resolution of the differential diagnosis and assignment of cell type. Diagnostic electron microscopy, in coordination with histopathology and clinical information, will often play a significant role in solving complex problems involving the differential diagnosis of large cell undifferentiated neoplasms.