Extranodal Nktcell Lymphoma Of Nasal Type

General: Extranodal NK/T-cell lymphoma of nasal type (or "NK/T-cell lymphoma") is most prevalent in Asia, Mexico, and South America, but occurs in other ethnic groups as well.102'103 The term "NK/T-cell" reflects the finding that while the majority of cases appear to represent neoplasms of NK cells, a subset are thought to be of T-cell type. In some cases, it may not be possible to distinguish with certainty whether the neoplastic cells represent T-cells or NK-cells. Most commonly, this lymphoma arises within the nasal cavity, but essentially identical cases may occur at other extranodal sites including skin, testis, soft tissue, and GI tract.

Pathology: The morphologic findings in NK/T-cell lymphoma are somewhat variable. In most cases, a diffuse proliferation of small- to intermediate-sized lym-phoid cells are present, but some cases display numerous large, even anaplastic, lymphoid cells.102-104 A characteristic feature of this neoplasm is that the proliferation often centers around and infiltrates vessel walls. There is often associated vascular destruction and extensive necrosis, which in some cases can obscure the malignant infiltrate.

Immunophenotype: The malignant cells in NK/T-cell lymphoma typically display a CD2+, CD56+, surface CD3 —, and cytoplasmic CD3e+ phenotype. There is consistent expression of cytotoxic proteins such as granzyme B and TIA1.102'105 Nearly all cases are EBV-positive, especially those arising in the nasal cavity, and in Asian patients. The association with EBV may be somewhat less strong in Western populations and in cases arising at nonnasal sites.105-107

Molecular genetics: Most cases represent malignancies of true NK cells and so lack clonal rearrangements of the T-cell receptor genes. In a subset of cases, however, clonal rearrangements may be detected, consistent with a true T-cell origin. In EBV positive cases, clonality of the episomal EBV DNA can also usually be demonstrated. The most frequent cytogenetic abnormality is del(6q), although this abnormality is also found in many other forms of lymphoma. There is currently little information available regarding other possible recurrent cytogenetic abnormalities.108

0 0

Post a comment