Pathology of non-hodgkin and hodgkin lymphomas

Non-Hodgkin lymphomas (NHLs) are neoplasms derived from lymphocytes. Approximately 85% of all tumors are derived from B cells, with the remaining NHLs derived from lymphocytes of T- or NK-cell lineage or rarely from histiocytes. Classification is a key component to advances in the understanding of NHLs and classification has evolved greatly over the years, from purely morphologic systems to the inclusion of immunophenotypic and molecular data. Recent applications of high throughput methods to the study of NHLs have contributed to our understanding and the recognition of distinct entities. The current consensus classification of NHLs is that of the World Health Organization (WHO) which was updated in 2016. The current classification recognizes approximately 90 entities. In the WHO system entities are defined on the basis of clinical, histologic, immunophenotypic, and molecular features. Although highly useful, the WHO classification should not “fix knowledge in time.” It is expected that knowledge will continue to evolve and that a number of changes to the system will be required at the time the next edition will be published.