11 - Hodgkin Lymphoma

Abstract

Hodgkin lymphoma (HL) is a clonal, malignant lymphoproliferation originating from germinal-center B cells. The malignant cells usually represent only a small minority (0.1% to 2%) of the total cellular population of involved tissues. The World Health Organization (WHO) classification discerns two major groups of Hodgkin lymphoma: classical HL (CHL) and nodular lymphocyte-predominant HL (NLPHL), which differ both clinically and pathologically. Histopathologic diagnosis of CHL is based on the identification of diagnostic Hodgkin and Reed-Sternberg (H/RS) cells in an appropriate inflammatory background, and the composition of the background dictates the subclassification. Although CHL usually shows a typical morphology, current diagnostic criteria include the characteristic immunophenotype of the neoplastic population, with positivity for the CD30 and CD15 antigens, lack of CD45, and an inconsistent and heterogeneous expression of lineage-specific lymphoid markers. In contrast, NLPHL is characterized by the presence of rare neoplastic cells expressing a broad range of B-cell markers including CD20, termed LP (for lymphocyte-predominant) cells in a background usually dominated by B cells arranged in follicular fashion. Despite the now-established B-cell origin of the neoplastic cells, and based on the clinical and pathologic peculiarities of this disease, HL remains separated from other lymphomas, termed non-Hodgkin lymphomas (NHL) for historical reasons, in the updated WHO classification.