Chapter 78 - The Pathologic Basis for the Classification of Non-Hodgkin and Hodgkin Lymphomas

Abstract

The classification of malignant lymphomas has undergone significant changes over the past 50 years. The current approach is based on the integration of morphologic, phenotypic, genetic, and clinical features that allows the identification of distinct disease entities. This practical approach to lymphoma categorization formed the basis of the Revised European-American Classification of lymphoid neoplasm (REAL) and was adopted by the World Health Organization (WHO) in its classification of neoplasm of the hematopoietic and lymphoid tissues, revised most recently in 2017. The WHO classification represents a significant achievement in terms of cooperation, communication, and consensus among pathologists, hematologists, and oncologists. Furthermore, it recognizes that for any classification system to be viable and applicable, it should evolve and incorporate new data resulting from emerging technologies in the field of hematopathology, such as results from genome-wide large-scale sequencing studies. These studies have led to the identifications of new prognostic and diagnostic categories, and provide insight into therapeutic targets based on a better understanding of molecular mechanisms of transformation. This chapter focuses on the classification of neoplasms derived from mature B cells, T cells, and natural killer (NK) cells with emphasis on malignant lymphoma. It provides a framework for subsequent chapters on Hodgkin and non-Hodgkin lymphomas in reviewing the major entities according to the WHO classification.