Changes in diagnosis of non-Hodgkin's lymphomas over time.

The question is raised as to whether changes in criteria for the diagnosis of non-Hodgkin's lymphomas, both clinical and pathological, have changed over the past four decades in sufficient scale to create a spurious increase in the apparent incidence of this grouping of disease. In the decade of the 1970s refinement in histomorphological criteria for the diagnosis of Hodgkin's disease resulted in as many as 10-15% of cases which previously would have been diagnosed as Hodgkin's disease being diagnosed instead as non-Hodgkin's lymphoma. Other considerations, including distinction of non-Hodgkin's lymphomas from leukemias and plasma cell myelomas, and recent recognition of angioimmunoblastic lymphadenopathy and extranodal "pseudolymphomas" as variant forms of non-Hodgkin's lymphoma, appear to have added only marginally to the total of reported cases. It is concluded that the increase in reported incidence of non-Hodgkin's lymphoma cannot be explained on the basis of changes in diagnostic criteria.