Morphologic and immunophenotypic variants of nodal T-cell lymphomas and T-cell lymphoma mimics

Given their relative rarity, one of the primary diagnostic difficulties in nodal T-cell lymphomas is recognizing their range of histologic patterns. This is complicated by the fact that most mature T-cell lymphomas retain some functional characteristics of nonneoplastic T cells, ie, the capacity to secrete cytokines and costimulate immune cell growth, and, thus, are associated with obscuring nonneoplastic immune cells. Sessions 2 and 3 of the Society for Hematopathology/European Association for Haematopathology Workshop focused on these issues and conditions that may simulate T-cell lymphomas. We summarize salient features of presented cases, including the varied patterns seen in angioimmunoblastic T-cell lymphoma (AITL) and other more poorly characterized morphologic and functional nodal T-cell lymphoma subsets. Many cases illustrated the difficulties distinguishing AITL from peripheral T-cell lymphoma, unspecified, when the neoplasms manifest only some AITL features. The usefulness of separately classifying T-cell lymphomas that demonstrate follicular, perifollicular, or T-zone patterns of infiltration; significance of immunophenotypically distinct subsets that express cytotoxic markers or have features of central memory T cells; diagnostic difficulties posed by B-cell proliferations that accompany T-cell lymphomas; and T-cell lymphoma mimics related to genetic disorders, immune dysregulation, and drug reactions are also discussed.