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The term peripheral T-cell lymphoma (PTCL) is used to describe lymphoid neoplasms of mature T-cell lineage, as opposed to tumors of thymic origin. The terms postthymic and mature T-cell lymphoma also have been used to describe these tumors. PTCLs represent approximately 10% of all NHLs in most European and US studies but are more common in other parts of the world (1–3). Incidences are higher in Asian populations, possibly related to a high prevalence of human T-cell lymphotrophic virus type 1 (HTLV-1) and Epstein– Barr virus.

The International Lymphoma Study Group (ILSG) incorporated morphologic, phenotypic, molecular, and clinical information in the REAL (Revised European American Lymphoma) classification. The revision provided the basis for WHO (World Health Organization) classification with the following changes: PTCLs were divided into nodal, extranodal, and leukemic types; cutaneous and systemic anaplastic large-cell lymphomas (ALCL); updated terminology with subcutaneous panniculitis-type and hepatosplenic gd T-cell lymphomas were recognized as separate entities (Table 9-1) (1).

Table 9–1. World Health Organization Classification of T-Cell Lymphomas

The most common histologic subtype is classified as PTCL not "otherwise specified" and accounts for approximately 55% of all PTCL. The second most common PTCL, ALCL, accounts for 17% of all PTCL, and angioimmunoblastic T-cell lymphoma (AITL) accounts for 13%. Other types of PTCL are rare, each <5% of all cases. Unlike B-cell lymphomas, the classification of T-cell neoplasms requires much more clinicopathologic correlation.

Patients with T-cell lymphomas are usually adults with generalized lymphadenopathy as well as frequent involvement of the skin, spleen, bone marrow, and blood. Although the subtypes of PTCL are histologically distinct, they share a very aggressive clinical course and, with the exception of ALK-positive ALCL, a poor response to conventional therapy.

The pathologic appearance and immunophenotype may vary within a given subtype. Therefore, diagnosis is usually based on a combination of clinical presentation, pathology, molecular findings, and factors that may be unique to each subtype. T-cell receptor rearrangements are found in a majority of lymphomas, but can be inconsistent.

Prognosis varies according to the subtype of PTCL. With the exception of patients with ALK+ ALCL who can be successfully treated with standard anthracycline-based chemotherapy and patients with stage ...

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