Classification And Clinicopatholocial Features

In the past, classification of T-cell lymphoid malignancies has been controversial, with no internationally accepted schema. The previously accepted morphology-based Working Formulation relied on morphology alone, and did not consider T-cell malignancies as separate and distinct entities. Rather, T-cell lymphomas that occurred infrequently and generally had a poor prognosis were included in different pathologic subtypes (diffuse-mixed, large cell, and lymphoblastic) and were treated like their B-cell counterparts.3 Subsequently, the Revised European-American classification of lymphoid neoplasms (REAL)4 has subdivided all lymphomas into B-cell and T-cell lymphomas to avoid the confusion created by the Working Formulation. The REAL classification further subdivides T-cell lymphoid malignancies into two major groups based on the T-cell maturation stage: precursor T-cell neoplasms and peripheral T-cell neoplasms. Furthermore, the peripheral T- and NK-cell neoplasms are subdivided into additional categories, with some provisional subtypes. Thus, the REAL classification was a major advance in the characterization of lymphoid malignancies, because it recognized that the site of disease presentation is a significant aspect of disease biology, with extranodal T-cell lymphomas being inherently different from nodal subtypes. Following the publication of the REAL classification in 1994, new findings regarding some categories of lymphoma clarified the status of entities that were listed as provisional in the REAL classification, particularly among the T-cell lymphomas. The currently used WHO classification is based on the principles established by the REAL classification and incorporates minor additional modifica-tions.15 Besides the precursor T-cell neoplasms, this classification includes 14 subgroups among the mature T- and NK-cell malignancies. Since the site of disease presentation represents a key aspect of disease biology and clinical course, an attempt is made to give it a more prominent role in subgroup characterization, leading to the classification of disease subtypes as being primarily leukemic, nodal, extranodal, or cutaneous (Table 60.1).

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