The non-hodgkin lymphomas

The non-Hodgkin lymphomas (NHL) are a heterogeneous group of over forty lymphoid neoplasms that have undergone a major redefinition over the last twenty-five years, in part due to advances in immunology and genetics as well as implementation of the WHO classification system. NHLs are considered clonal tumors of B-cells, T-cells, or natural killer (NK) cells arrested at various stages of differentiation, regardless of whether they present in the blood (lymphoid leukemia) or lymphoid tissues (lymphoma). In the United States, the age-standardized NHL incidence rate (per 100,000) doubled from 1973 (10.2) to 2004 (21.4) and then stabilized, while five-year relative survival rates improved from 42% in 1973 to 70% in 2004. Established risk factors for NHL or specific NHL subtypes include infectious agents (HTLV-1, HIV, EBV, HHV8, HCV, H. pylori), immune dysregulation (primary immunodeficiency, transplantation, autoimmunity, and immunosuppressive drugs), family history of lymphoma, and common genetic variants identified by genome-wide association studies.