Mediastinal gray zone lymphoma.

Introduction The current classification of lymphoid neoplasms is based on the integrated utilization of morphological, immunohistochemical, genetic and clinical criteria to define disease entities, which putatively have their origin in a “normal counterpart” in the immune system. The application of modern immunophenotypic and molecular genetic techniques in routine diagnosis has made it possible for most lymphomas to be successfully diagnosed and classified as one of the currently recognized distinct disease entities. Nevertheless, there are cases that do not follow this principle and show overlapping or borderline morphological, biological and clinical features between various types of lymphomas. The updated 2008 World Health Organization (WHO) classification of tumors of hematopoietic and lymphoid tissues recognized this problem and introduced two new provisional categories of B-cell lymphoma, unclassifiable, one with features intermediate between diffuse large B-cell lymphoma (DLBCL) and Burkitt’s lymphoma and the second, which is the topic of this review, with features intermediate between DLBCL and classical Hodgkin’s lymphoma (CHL). This second provisional category recognizes cases that usually occur in the mediastinum and have features of both nodular sclerosis CHL (NSCHL) and primary mediastinal large B-cell lymphoma (PMBL). In this review PMBL will be briefly considered in order to provide the framework for understanding the concept of mediastinal gray zone lymphoma.