New approaches to the classification of the lymphomata.

Our recently proposed functional approach to and classification of the malignant lymphomata based upon the T and B cell systems, lymphocyte transformation and their development as blocks or a "switch on" in lymphocyte transformation has been reviewed. This functional classification contains 5 major groups: (a) U cell or undefined for those proliferations without specific markers; (b) T cell; (c) B cell; (d) histiocytes as macrophages; (e) unclassifiable for those technically insufficient for specific cytological classification. Retrospective study of several case populations indicates that the majority of non-Hodgkin's lymphomata exhibit features of follicular centre cell (FCC) lymphomata of either cleaved or non-cleaved types. The prognostically favourable status of nodular lymphomata seems to result from the retained capability of follicle formation by FCC types with limited abnormality. Lymphomata of large cell types previously classified as histiocytic lymphoma or reticulum cell sarcoma predominantly resemble transformed lymphocytes and rarely exhibit features of histiocytes as macrophages. They are designated "immunoblastic sarcoma" when they occur as large transformed lymphocytes and may have either T or B cell immunological markers. Immunoblastic sarcoma has been observed to develop in individuals with chronic abnormal immune states, Sjögren's syndrome, alpha chain disease, in patients on immunosuppression therapy for graft rejection and in senescence. There is accumulating evidence of lymphomata of T cells but none are firmly established. These include Sézary's syndrome, mycosis fungoides and the convoluted lymphocyte type, prev-ously included designated as acute lymphocytic leukaemia with mediatinal mass. The results of initial functional studies provide support for the proposed classification and indicate that the modern pathological investigative approach requires the collection of fresh lymphomatous tissue and an integrated immunocytochemical and morphological approach for the precise characterization of human lymphoma cell types.