Angioimmunoblastic T-cell lymphoma

Overview
Angioimmunoblastic T-cell lymphoma (AILT) is a mature T-cell lymphoma with systemic characterized by a polymorphous lymph node infiltrate showing a marked increase in follicular dendritic cells (FDCs) and high endothelial venules (HEVs) and systemic involvement. It is also known as immunoblastic lymphadenopathy (Lukes-Collins Classification) and AILD-type (lymphogranulomatosis X) T-cell lymphoma (Kiel Classification) The ICD-O code is 9705/3.

Epidemiology
The typical patient with angioimmunoblastic T-cell lymphoma (AILT) is either middle-aged or elderly, and no gender preference for this disease has been observed. AILT comprises 15-20% of peripheral T-cell lymphomas and 1-2% of all non-Hodgkin lymphomas.

Etiology
This disease was originally thought to be a premalignant condition, termed angioimmunoblastic lymphadenopathy, and this atypical reactive lymphadenopathy carried a risk for transformation into a lymphoma. Currently, it is postulated that the originating cell for this disease is a mature (post-thymic) CD4+ T-cell that arises de novo, although some researchers argue that there is a premalignant subtype of this disease. The Epstein Barr virus (EBV) is observed in the majority of cases, and the virus has been found in the reactive B-cells that comprise part of the polymorphous infiltrate of this disease and in the neoplastic T-cells. Immunodeficiency is also seen with this disease, but it is thought to be a sequela to the condition and not a predisposing factor.

Clinical Presentation
Patients with this disease usually present at an advanced stage and show systemic involvement. The clinical findings typically include a pruritic skin rash and possibly edema, ascites, pleural effusions, and arthritis.

Laboratory Findings
The classical laboratory finding is polyclonal hypergammaglobulinemia, and other immunoglobulin derrangements are also seen, including hemolytic anemia with cold agglutinins, circulating immune complexes, anti-smooth muscle antibodies, and positive rheumatoid factor.

Sites of Involvement
Due to the systemic nature of this disease, neoplastic cells can be found in lymph nodes, liver, spleen, skin, and bone marrow.

Lymph node
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. Hyperplastic germinal centers and Reed-Sternberg cells can also be seen.

Immunophenotype
AILT typically has the phenotype of a mixture of CD4+ and CD8+ T-cells, with a CD4:CD8 ratio greater than unity. Polyclonal plasma cells and CD21+ follicular dendritic cells are also seen.

Genetic Findings
Clonal T-cell receptor gene rearrangements are detected in 75% of cases, 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. Similarly, EBV-related sequences can be detected most cases, usually in B-cells but occasionally in T-cells. . Trisomy 3, trisomy 5, and +X are the most frequent chromosomal abnormalities found in cases.