Peripheral T Cell Lymphoma Unspecified

Definition

Morphologically and immunophenotypically heterogeneous group of nodal T cell lymphomas that do not meet the diagnostic criteria of one of the other WHO-defined T-cell lymphoma categories

Lymphoepithelioid cell lymphoma / Lennert lymphoma / T cell lymphoma with high content of epithelioid lymphocytes
Pleomorphic T-cell lymphoma
T cell lymphoma, NOS and diffuse small cleaved cell, diffuse mixed small and large cell, diffuse large cell, and immunoblastic types
T-zone lymphoma

Morphologic features are highly variable
- Cell size usually medium to large, but can be small
- Pattern of infiltration usually diffuse
  - T-zone variant
    - Malignant infiltrate spares follicles
    - Cytologic atypia is subtle
    - Vascular/mixed inflammatory background
- Cytologically malignant features usually present
  - Nuclear pleomorphism and irregular nuclear contour
  - Vesicular or hyperchromatic chromatin pattern
  - Prominent nucleoli
- Background often vascular with admixed plasma cells, eosinophils, histiocytes, immunoblasts
  - Lymphoepithelioid cell variant (“Lennert lymphoma”)
    - Clusters of epithelioid histiocytes
    - Malignant infiltrate with subtle cytologic atypia
Accompanying B cell proliferation in ~20%
- Diagnosis of diffuse large B cell lymphoma requires sheets of monoclonal large B cells
- Diagnosis of plasmacytoma requires sheets of monoclonal plasma cells
- Molecular evidence of B cell clonality is NOT sufficient for diagnosis of B cell lymphoma/plasmacytoma

Dita Gratzinger MD PhD
Yasodha Natkunam MD PhD

Department of Pathology
Stanford University School of Medicine
Stanford CA 94305-5342

Initial posting : October 8, 2007