Aggressive lymphoma 2016: revision of the WHO classification

Aggressive lymphomas are a heterogeneous group of malignancies reflecting clinical, biological and pathological diversity. Diffuse large B‑cell lymphoma is the most common histological subtype and therefore will constitute the key aspect in this article. This lymphoma affects patients of all age groups with wide range presentations concerning localization, morphology and molecular mechanisms. The median age at presentation is about 60 years with a slight male preponderance. Up to 50% of patients present with advanced disease. About 70% of these lymphomas occur nodal, about 30% extranodal, the most common sites of the latter being the gastrointestinal tract, Waldeyer's ring, skin, cerebrum, mediastinum, testis, salivary gland, thyroid and bone. However, diffuse large B‑cell lymphoma can involve virtually any organ.Since the last WHO classification 2008 the adoption of new genomic technologies has provided new insights into the biology of these lymphomas and led to the identification of distinct separate molecular entities and novel pathogenic pathways. These findings induced an expanding number of entities in the new WHO classification of 2016, the knowledge of which is essential concerning treatment options and survival of the patients. Therefore, the clinicians request an accurate diagnosis from the investigating pathologist, which can be quite challenging. The diagnosis of lymphomas requires multiple immunohistochemical studies, and often additional tests, such as fluorescent in situ hybridization and/or polymerase chain reaction techniques and occasionally, in particular cases, next generation sequencing for identification of recurrent somatic mutations. This review summarizes relevant aspects of the new WHO classification in aggressive B‑cell lymphomas, especially from a haematopathologist's point of view.