Peripheral T-cell lymphomas not otherwise specified (PTCL-NOS) include a heterogeneous group of diseases involving lymph nodes and extra nodal sites deriving from the clonal expansion of mature T-lymphocytes bearing clonally rearranged TCR genes.

The cell of origin is an activated mature CD4+ lymphocyte.
The phenotype is usually CD4+/CD8-, TCRβ+ whereas the expression of CD7 and CD5 may be low. Occasionally, CD30 may be positive.

There is geographic variation in the incidence of T-cell lymphoma. PTCL-NOS accounts for approximately 4-7% of all non Hodgkins lymphomas and for 30-70% of all mature T-cell lymphomas.

The disease runs an aggressive clinical course.

The proliferation effaces the lymph node architecture, with paracortical or diffuse growth pattern. The cells are medium-to-large sized, with irregular nucleus, distinct nucleoli. Mitotic figures may be numerous.

Anthracycline-based regimes such as CHOP yields unsatisfactory results with lower CR rates than in B-cell diffuse large cell lymphomas and high relapse rate. Intensive regimens such as hyperCVAD with or without autologus bone marrow transplantation may be effective in this type of lymphoma, though the superiority of this approach over conventional treatment has not been definitely proven.

Reported failure free survival rates ranged between 12 and 45% (Armitage, 2006).