Clinico-pathological forms of peripheral T- and NK-cell lymphomas

Malignant lymphomas, originating from peripheral T or NK cells, are rare tumours in Europe and account for less than 10% of all malignant lymphomas. In this review, the salient features of the more frequently occurring entities derived from T or NK cells will be presented. Nasal NK/T cell lymphoma is mainly found in the nose and paranasal sinuses:and often, but not always, display an angiocentric growth pattern leading to coagulation necrosis. The tumor cells consistently express CD56, CD2 and the EBER molecules encoded by the Epstein-Barr virus. Clonal T cell receptor gene rearrangements are often absent indicating, in the majority of cases, a derivation of these tumors from NK cells. Enteropathy-type intestinal T-cell lymphomas often arise in patients with celiac disease and have a dismal prognosis. The tumour cells express T cell antigens, CD103 and cytotoxic molecules, but are negative for CD4. Approximately 20% of the cases display CD56 mostly in combination with CD8. Recently, an early purely intraepithelial form of this tumour was identified. Histologically these cases resemble celiac disease, however the intraepithelial lymphocytes often exhibit an abnormal immunophenotype with absent CD8 and T-cell-receptor protein expression, and, they are clonal by molecular analysis. Clinically, the patients suffer from refractory sprue or ulcerative jejunitis. The prognosis is bad with the patients often dying from malnutrition or an invasive tumour-forming T-cell lymphoma. Angioimmunoblastic T-cell lymphoma is defined by characteristic morphological findings (atypical lymphoid cells in part with pale cytoplasm,arborizing high endothelial venules and,targe FDC-meshworks) as well as clinical features (systemic symptoms, signs of a dysregulated immune response). Peripheral T-cell lymphomas,that do not fit into a distinct entity, are classified in the REAL and the new WHO classifications as peripheral T-cell lymphomas unspecified. These display a broad morphological spectrum (including the T-cell lymphomas of different cell sizes, Lennert's lymphoma and T-zone lymphoma of the Kiel-classification) and in general are clinically aggressive.