Definition

Hodgkin lymphomas (HLs) encompass at least two morphologically, biologically, and clinically distinct subtypes of germinal center-derived B-lineage lymphoma [1]. Morphologically, these lymphomas are characterized by a small number of large atypical malignant cells (Hodgkin, Reed–Sternberg, and lymphocytic and histiocytic, or L&H, cells) set in the background of benign inflammatory elements, with or without associated fibrosis, that make up the bulk of the tumoral tissue. The neoplastic cells are typically surrounded by rosettes of T-lymphocytes. In the nodular lymphocyte-predominant type of HL (NLPHL), the neoplastic cells exhibit overt B-lineage differentiation. In the classical type of HL (cHL), these cells exhibit an aberrant differentiation program, and have a characteristic, CD15-positive, CD30-positive, CD45 (leukocyte common antigen)-negative immunophenotype. Classical HL is further subclassified according to the growth pattern and cellular milieu, into the lymphocyte-rich (LR), nodular sclerosis (NS), mixed cellularity (MC), and lymphocyte-depleted (LD) subtypes.

Epidemiology

HL has a bimodal age distribution throughout the world, with a peak of incidence at 15–34 years and a second peak after the age of 60 years [2]. A significant proportion of cases occurs in the pediatric age group, the majority of which present in adolescents, with only a minority of cases seen in patients under the age of 10 years [3, 4]. In the United States and Western European countries, the incidence of HL is <1 per million in children under 10 years of age, and approximately 29 per million in adolescents (10–19 years of age) [3, 4].