Angioimmunoblastic T-cell lymphoma (AITL, sometimes misspelled AILT, formerly known as "angioimmunoblastic lymphadenopathy with dysproteinemia"[2]: 747 ) is a mature T-cell lymphoma of blood or lymph vessel immunoblasts characterized by a polymorphous lymph node infiltrate showing a marked increase in follicular dendritic cells (FDCs) and high endothelial venules (HEVs) and systemic involvement.[1]
AITL was originally thought to be a premalignant condition, termed angioimmunoblastic lymphadenopathy, and this atypical reactive lymphadenopathy carried a risk for transformation into a lymphoma. It is postulated that the originating cell for AITL is a mature (post-thymic) CD4+ T-cell that arises de novo,[1] or that the disease has a premalignant subtype.[5][6] The Epstein–Barr virus (EBV) is observed in the majority of cases,[1] being identified in the reactive (i.e. non-malignant) B-cells that comprise part of the polymorphous infiltrate of AITL.[7] These EBV+ B cells have numerous non-malignant crippling mutations, often proliferate excessively, and in some cases may transform into EBV+ B cell lymphomas. The other cell types in these infiltrates, including the malignant TFH cells, are EBV negative. While the World Health Organization (2016) has classified these EBV-associated cases as one of the Epstein-Barr virus-associated lymphoproliferative diseases (see EBV+ angioimmunoblastic T cell lymphoma, the role of the virus in the development and progression of EBV+ angioimmunoblastic T cell lymphoma is unclear.[8] Immunodeficiency is also seen with AITL, but it is a sequela and not a predisposing factor.[1]
The normal architecture of a lymph node is partially effaced by a polymorphous infiltrate and residual follicles are commonly seen. The polymorphous infiltrate consists of lymphocytes of moderate size with pale/clear cytoplasm and smaller reactive lymphocytes, eosinophils, histiocytes, plasma cells, and follicular dendritic cells. In addition, blast-like B-cells are occasionally seen. A classic morphological finding is the aborization and proliferation of high endothelial venules.[1] Hyperplastic germinal centers and Reed-Sternberg-like cells can also be seen.[9][10]
Clonal T-cell receptor gene rearrangements are detected in 75% of cases,[11] and immunoglobin gene rearrangements are seen in 10% of cases, and these cases are believed to be due to expanded EBV-driven B-cell populations.[12] Similarly, EBV-related sequences can be detected in most cases, usually in B-cells but occasionally in T-cells.[7][13]Trisomy 3, trisomy 5, and +X are the most frequent chromosomal abnormalities found in AITL cases.[14][15]
Treatment
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Epidemiology
The typical patient with angioimmunoblastic T-cell lymphoma (AITL) is either middle-aged or elderly, and no gender preference for this disease has been observed.[1] AITL comprises 15–20% of peripheral T-cell lymphomas and 1–2% of all non-Hodgkin lymphomas.[16]
^Frizzera G, Kaneko Y, Sakurai M (January 1989). "Angioimmunoblastic lymphadenopathy and related disorders: a retrospective look in search of definitions". Leukemia. 3 (1): 1–5. PMID2642571.