New aspects of the histopathology of Hodgkin's lymphoma

Hodgkin's lymphoma is a diagnostic challenge for pathologists. This challenge is primarily due to the paucicellularity of the tumor, in which the lymphoma cells make up less than 1 % of all cells. The vast majority of cells in the tissue are non-neoplastic inflammatory cells and constitute the microenvironment. The composition of this microenvironment is used for the histological classification of classical Hodgkin's lymphoma subtypes. The aim of the review article is the presentation of recent developments in the diagnosis, classification and prediction of prognosis of Hodgkin's lymphomas by pathology. A selective search of the literature was carried out with reference to personal experience as a reference pathologist within the framework of the Competence Network Malignant Lymphoma (registered) Society. Prognostic information can be derived from the microenvironment as has been shown by gene expression analyses. The lymphoma cells, consisting of Hodgkin and Reed-Sternberg cells, can be immunohistochemically detected by pathologists within the microenvironment using well-known markers, such as CD30, However, in recent years new diagnostic markers have been developed which facilitate the diagnostics. These include transcription factors, such as PAX5, BOB1 and OCT2 and their detection by immunohistology produces important criteria for the definition of Hodgkin's lymphoma. These advances in molecular and histological analyses have redefined the diagnostic boundary zones of lymphoma in combination with the description of clinical symptoms which can imitate Hodgkin's lymphoma, such as mucocutaneous ulcers associated with Epstein-Barr virus.