Workshop report on Hodgkin’s disease and related diseases (‘grey zone’ lymphoma)

Abstract
Despite advances in immunohistochemistry and molecular biology, the distinction between classical Hodgkin's lymphoma and related diseases such as nodular lymphocyte-predominant Hodgkin's disease, T-cell rich large B-cell lymphoma or ana-plastic large cell lymphoma has remained difficult in rare cases. Lack of clear-cut diagnostic criteria represents a problem for both the pathologist and the clinician. To delineate this ‘grey zone’ between classical Hodgkin's lymphoma and non-Hodgkin's lymphoma (NHL) and to develop criteria for classification of such cases, 12 expert hematopathologists each submitted one to five borderline cases to a workshop. Cases were reviewed and classified at a multi-headed microscope and criteria were established for the diagnosis of questionable cases. Well established entities such as classical Hodgkin's lymphoma, anaplastic large-cell lymphoma and TCRBCL were defined more strictly and cases with unusual morphology or antigen expression could be identified. A distinctive subset of cases representing mediastinal large B-cell lym-phomas with features of Hodgkin's lymphoma was identified.