Clinical importance of analysing malignant tumours of uncertain origin with immunohistological techniques.

The value of immunohistology in the histopathological diagnosis of malignant tumours was evaluated in a series of 120 consecutive routinely processed biopsy specimens, all of which had been referred by histopathologists because of diagnostic difficulties. The specimens were analysed by means of a panel of monoclonal and polyclonal antibodies reactive with antigens which resist routine tissue processing. The tumours had previously been considered unclassifiable (24 cases) or categorised as probable carcinomas (43 cases) or lymphomas (53 cases). All but 8 of the 120 cases could be classified with the immunohistological technique. Lymphoma was the commonest diagnosis (66%) and accounted for 29 of the 43 cases initially thought most likely to be anaplastic carcinomas. Immunohistological methods can now resolve the majority of difficulties arising over the histological diagnosis of malignant tumours, and these methods should therefore be used on a wide scale by diagnostic histopathology laboratories.