From a pathologist's point of view: Histiocytic cells in Hodgkin lymphoma and T cell/histiocyte rich large B cell lymphoma.

While tumor cells were the focus of research for many years, only recently have attempts been made to understand the role of the reactive bystander cells in malignant lymphomas. In certain types of lymphomas, such as Hodgkin lymphoma and T cell/histiocyte rich large B cell lymphoma, more than 90% of the infiltrate represent non-neoplastic cells, and these have important functions for the development and progression of the tumor. Among the bystander cells are histiocytes of particular importance, which vary largely in number, shape and quality among different patients. In the present review, recent findings on the prognostic impact of histiocytic bystander cells in these lymphomas, as well as their molecular characteristics, are discussed. A better understanding of the role of these histiocytes may provide new concepts for diagnosis and treatment.