Classification and differential diagnosis of 20 problem cases of occidental malignant T-cell lymphomas.

Twenty malignant T-cell lymphomas are described in which the initial histological diagnosis was equivocal. Among lymphoma entities initially falsely interpreted on pure morphological grounds were Hodgkin's disease, lymphoepithelioid cellular lymphoma, immunoblastic lymphoma with epithelioid cells, malignant histiocytosis, histiocytosis X, centroblastic lymphoma, undifferentiated carcinoma, and undifferentiated tumour. Variations in the expected mean survival of initially diagnosed tumours and T-cell lymphomas confirm the need for immunohistological cell typing in lymphoma classification.