An overview of the classification of non-Hodgkin's lymphomas: an integration of morphological and phenotypical concepts.

An analysis of trends in the incidence of non-Hodgkin's lymphoma requires an understanding of individual disease entities within this broad group. The non-Hodgkin's lymphomas represent a diverse group of malignancies that have in common an origin from lymphoid cells. Nevertheless, these disorders are heterogeneous in their clinical behavior, morphological appearance, cellular origin, etiology, and pathogenesis. A modern classification of non-Hodgkin's lymphomas must include an integration of morphological, immunophenotypical, and molecular concepts in order to delineate individual diseases within this broad group. Existing classification schemes such as the working formulation, while they may be useful in providing a guide to clinical management, cannot provide this information in the absence of other data. This point is most readily made with the low-grade B-cell lymphomas which include follicular lymphomas, mantle cell lymphomas, small lymphocytic lymphomas, immunosecretory disorders, and lymphomas of mucosa-associated lymphoid tissues. Each of these malignancies has a distinct phenotype and genotype, and indubitably each has a different etiology. The postthymic T-cell tumors are equally diverse. Analysis of epidemiological data from cancer registries must include a recognition that our ability to recognize individual diseases from historical data is limited. Studies of trends in the non-Hodgkin's lymphomas should attempt to delineate biological markers that may be of relevance to pathogenesis in both historical and prospectively accrued cases.