Hematologic malignancies of cytotoxic cells: Introduction

Abstract

THIS ISSUE OF Seminars in Hematology is devoted to leukemias and lymphomas of killer cell origin. These hematologic malignancies can be derived from either cytotoxic T lymphocytes (CTL) or natural killer (NK) cells. These lymphoid malignancies are much less common than B cell lymphoproliferative disease. For example, it is estimated that approximately 10% of non-Hodgkin’s lymphomas fall into the category of either T-cell or NK cell disorders. The relative infrequency of such patients, varied terminology, recent recognition of most of these entities, and perhaps most importantly lack of an easily determined marker of clonality for the NK cell neoplasms has led to a considerable degree of confusion in this area of hematologic malignancies. Therefore one goal of the current issue is to summarize diagnostic criteria and clinicopathologic features of hematologic malignancies originating from CTL or NK cells. Elaine Jaffe and colleagues review the current classification of CTL and NK cell lymphomas based on the World Health Organization (WHO) system. Jaffe et al emphasize that the WHO classification is based on a multiparameter approach. In particular, they highlight the important role of the clinical presentation in classification as these malignancies show great morphologic diversity. In addition to providing a good overview of many of the entities discussed in further detail in subsequent chapters, other lesions such as the enteropathy type of T-cell lymphoma and subcutaneous panniculitis-like T-cell lymphomas are discussed in detail. Particularly valuable for discrimination of the differential diagnostic possibilities among this group of hematologic malignancies are the immunophenotypic properties. Jaffe’s group recently used granzyme M staining to distinguish NK lymphomas, T-cell lymphomas, and enteropathyassociated T-cell lymphomas from other lymphomas arising from cytotoxic precursors. The five chapters that follow focus on various aspects of large granular lymphocyte (LGL) leukemia. Clonal cytogenetic abnormalities and tissue invasion of marrow, spleen, and liver characterized the first description of LGL leukemia. Subsequently it was recognized that LGL leukemia could be derived from either T cells or NK cells, leading to the designations of T-LGL and NK-LGL leukemia, respectively. Lamy and Loughran provide an update on the clinical features of LGL leukemia. A fascinating aspect of LGL leukemia is the strong clinical association with autoimmune diseases such as rheumatoid arthritis. There may be a common pathogenesis and indeed LGL leukemia and Felty’s syndrome may be the same disease. There is also growing recognition that LGL leukemia may overlap clinically with disease states characterized by failure of hematopoiesis. The Mayo Clinic experience describing the association of LGL leukemia with either aplastic anemia or pure red cell aplasia is detailed by Go et al. Although not widely recognized, the most common identifiable