Peripheral T-cell lymphomas: diagnosis and management

The peripheral T-cell malignancies are a heterogeneous group of rare disorders that result from clonal proliferation of mature postthymic lymphocytes. They account for approximately 10% to 12% of all lymphoid neoplasms. The following entities are recognized in the World Health Organization (WHO) classification (Box 1): T-cell prolymphocytic leukemia (T-PLL); T-cell large granular lymphocyte leukemia (T-LGLL) and natural killer (NK)-cell leukemia; adult T-cell leukemia lymphoma (ATLL); cutaneous T-cell lymphomas (CTCL), including mycosis fungoides (MF) and Sezary syndrome (SS); and other extranodal and nodal peripheral T-cell lymphomas (PTCL). There is considerable geographic and racial variation in the incidence of different subtypes. PTCL, excluding AIDS-related complex, are more frequent in the Far East than in western countries. From a total of 96 cases of nonanaplastic PTCL that were reviewed in the Non-Hodgkin's Lymphoma Classification Project, the lowest frequency was in North America (3%) followed by an intermediate frequency in Europe and in Cape Town, South Africa, and significantly higher frequency in the Far East (18%). In some cases, this is related to the causal association between a particular T-cell malignancy and viruses, such as the Epstein-Barr virus (EBV) in nasal NK/T-cell lymphoma and human T-cell lymphotrophic virus 1 (HTLV-1) in ATLL. Although some of the peripheral T-cell malignancies, such as T-LGLL and early stage MF, may follow a benign protracted course, others have an aggressive clinical behavior and, apart from (ALCL), a poor response to conventional chemotherapy.