Classification of routinely processed anaplastic large cell tumours with a small panel of antibodies. An immunohistochemical study with clinical follow-up.

A proportion of anaplastic large cell tumours is difficult to classify on sections of routinely processed, paraffin-embedded tissue. Differentiation into large cell lymphoma, carcinoma, melanoma or sarcoma is important in order to assess prognosis and proper treatment. Although the use of immunohistochemistry has been reported in the differentiation between some of these types of neoplasms, no antibody panel, which can directly differentiate all of them, has been described. In the present study we evaluated the value of a panel of 5 antibodies for the classification of 29 anaplastic large cell tumours, which could not be classified by experienced pathologists using conventional histological and histochemical techniques. The panel, which can be used on routinely fixed paraffin-embedded tissue, consisted of 5 different antibodies directed against keratin, vimentin, the human milk-fat globule membrane antigen MAM-6, a melanoma associated antigen and common leucocyte antigen. The use of this panel directly resulted in a definite diagnosis in 95% of the cases and provided valuable information for the diagnosis in the remaining cases. The diagnosis was confirmed by additional marker studies and electron microscopy. Moreover, clinical follow-up, including treatment data, was in accordance with the diagnosis based on the panel.