Lymphoproliferative diseases of uncertain classification.

In spite of the recent progress in the biology and histogenesis of the lymphoproliferative diseases, many doubts still remain about their possible evolution. On the one hand, many cases have been studied showing a benign course in spite of a typical monoclonal phenotype; on the other, some clinically aggressive forms of lymphoproliferation prove to be polyclonal throughout their course, even when checked with highly sophisticated techniques. In this article we have reviewed, in both clinical and etiopathogenetic terms, the classification of these processes in the light of the new findings provided by extensive use of the most advanced investigational techniques of genotype and phenotype analysis. We have recognized three main groups of lymphoproliferative disorders of uncertain significance, based on pathophysiological, anatomical and developmental considerations: 1) lymphoproliferative diseases that take place on a background of either congenital or acquired immunodeficiency, referred to as "opportunistic lymphoproliferative disorders"; 2) lymphoproliferative diseases deriving from "mucosa associated lymphoid tissue" (MALT); 3) lymphoproliferative diseases of uncertain histogenesis, now classified as "T lymphomas". The opportunistic lymphoproliferative disorders, particularly in HIV+ patients and transplant recipients, often show developmental and etiopathogenetic features which may help to elucidate their natural history. Frequent involvement of Epstein-Barr virus and the related host's immune response patterns provide powerful tools to outline the alternative developmental pathways of such disorders.2+ Worthy of note is acute infectious mononucleosis which, though self-limiting when occurring in the immunocompetent host, may be considered as a lymphoproliferative process and sometimes shows some "aggressive'' morphological aspects. Special attention is paid to the obscure origin of Hodgkin's disease.(ABSTRACT TRUNCATED AT 250 WORDS)