Subcutaneous Panniculitislike Tcell Lymphoma

General: Subcutaneous panniculitis-like T-cell lymphoma (SPTCL) is an uncommon form of lymphoma (<1% of all NHLs) composed of cytotoxic T-lymphocytes.124-126 Patients typically present with multiple subcutaneous nodules, most commonly on the extremities and trunk. Frequently, SPTCL may be accompanied by a hemo-phagocytic syndrome with associated fevers, cytopenias and hepatosplenomegaly.125 This area is undergoing change in definitions depending on whether the tumor cells express 78-type or ap-type T-cell receptor.

Morphology: There is typically a diffuse infiltrate of small- to intermediate-sized lymphocytes throughout the subcutaneous tissues, often without sparing of the lobular septae.125 126 The infiltrate may extend into the dermis as well, although the dermal component is usually relatively minor (particularly in the ap-type). Areas of vascular invasion may be present, and there is frequent necrosis (particularly in the 78-type). Characteristically, the malignant cells tightly ring individual adipocytes. There may be accompanying histio-cytes, especially in areas of fat necrosis.

Immunophenotype: The malignant cells express cyto-toxic molecules including TIA1, granzyme B and perforin. Most cases are CD8+ and express the ap T-cell receptor.124'125 Approximately 25% of cases, however, express the 78 T-cell receptor. Many of these latter cases lack expression of both CD4 and CD8 and are positive for CD56. There is no association with EBV. It is these 78-type lymphomas that appear to have an aggressive clinical course. The ap-type appears to have an indolent course and is currently the only type accepted as SPTCL in the recently published WHO-EORTC classification of cutaneous lymphomas.127 The 78-type is now classified as a provisional entity (primary cutaneous 78-T-cell lymphoma.

Molecular genetics: Rearrangements of the T-cell receptor are usually detectable by PCR and/or Southern blot studies. EBV is absent. Currently, no characteristic cytogenetic abnormalities have been identified.

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