The malignant lymphomas are a group of lymphoproliferative disorders that are usually divided into Hodgkin’s disease and the non-Hodgkin’s lymphomas. These two disease entities have markedly different clinical characteristics. For instance, Hodgkin’s lymphomas commonly occur as localized areas of lymph node enlargement. They tend to spread to contiguous lymph node groups and do not commonly involve extranodal sites of disease. Further, they are cured in more than 75% of the cases. Non-Hodgkin’s lymphomas tend to be disseminated at presentation, will spread in a discontinuous fashion, and frequently involve extranodal areas. Further, the cure rates remain in the 30% to 40% range. The cell of origin in the non-Hodgkin’s lymphomas is usually a B cell but occasionally a T cell. The cell of origin in Hodgkin’s disease remains unknown.

An experienced hematopathologist is required to distinguish some forms of non-Hodgkin’s lymphoma from Hodgkin’s disease. However, the importance of the subclassification of the non-Hodgkin’s lymphomas is critical, as is detailed later.