The Non-Hodgkin’s Lymphomas

Abstract

Non-Hodgkin’ s lymphomas (NHLs) are malignant proliferations of the lymphoid tissues that can be distinguished from Hodgkin’s disease (see p. 173) by a variety of clinical and histological features. NHLs are more heterogeneous in their behavior and often have an extranodal involvement. The classification of NHLs continues to evolve. In the United States, the Rappaport classification and later the Working Formulation were used, in many European countries the Kiel classification was used. Recently, a new classification scheme was introduced, the Revised European American Lymphoma (REAL) classification. The REAL classification incorporates some of the recent progress in immunology and molecular biology and is discussed in Subheading 15.3. Considerations that enter into these classifications are the growth pattern (diffuse or follicular), the clinical experience (aggressive or high-grade versus indolent or low-grade), immunophenotype (B-, T-, or natural killer [NK]-cell markers) and genetic changes. Taken together, NHLs are more frequent than Hodgkin’s disease and have an incidence of about 8–15 new cases per year per 100,000 people. In recent years, the incidence of NHL has steadily increased. About 90% of the NHL are derived from a malignant B cell, the rest from T cells, NK cells, or undifferentiated cells. With some exceptions, NHLs are a disease of older persons, with an age median around 50–70 yr.