The role of immunoperoxidase techniques on paraffin embedded tissue in determining the histogenesis of undifferentiated thyroid neoplasms.

Twenty cases of undifferentiated thyroid tumours were reviewed histologically. In seven cases the histogenesis was difficult to determine using morphological criteria. Immunohistochemical staining with a panel of antibodies to lymphoid and epithelial cells, including monoclonal antibodies directed against the leucocyte common antigen, cytokeratin, and epithelial membrane antigen confirmed that four of these cases were lymphomas and that one was a medullary carcinoma. In the remaining two cases immunohistochemistry was unhelpful. In the thirteen histologically typical tumours, the immunohistochemical profile was in keeping with their histogenesis as determined by morphological criteria. Immunohistochemical staining with a panel of selected antibodies allows the reliable diagnosis of undifferentiated thyroid neoplasms, when this cannot be reached using routine histological techniques.