The term lymphoma describes a heterogenous group of malignancies with different biology and prognosis. In general lymphomas are divided into 2 large groups of neoplasms, namely non-Hodgkin lymphoma (NHL) and Hodgkin disease. About 85% of all malignant lymphomas are NHLs. The median age at diagnosis is the sixth decade of life, with some exceptions. (Burkitt lymphoma and lymphoblastic lymphoma occur in younger patients.) NHL includes many clinicopathologic subtypes, each with distinct epidemiologies; etiologies; morphologic, immunophenotypic, genetic, and clinical features; and responses to therapy.
Currently, several NHL classification schemas exist, reflecting the growing understanding of the complex diversity of the NHL subtypes. The Working Formulation, originally proposed in 1982, classified and grouped lymphomas by morphology and clinical behavior (ie, low, intermediate, or high grade). In the 1990s, the Revised European-American Lymphoma (REAL) classification attempted to apply immunophenotypic and genetic features in identifying distinct clinicopathologic NHL entities. The World Health Organization (WHO) classification further elaborates upon the REAL approach. This classification divides NHL into those of B-cell origin and those of T-cell and NK-cell origin.
For clinical oncologists, the most practical way of sorting the currently recognized types of NHL is according to their predicted clinical behavior; each classification schema contributes to a greater understanding of the disease, which dictates prognosis and treatment.
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