Angioimmunoblastic Tcell Lymphoma

General: Angioimmunoblastic T-cell lymphoma (AITL) accounts for 1-2% of NHL.91 Initially thought to represent an abnormal immune reaction, molecular studies have demonstrated this process to represent a clonal malignancy.92 Patients typically present at high stage with adenopathy, hepatosplenomegaly, and, often, bone marrow involvement. Systemic symptoms such as fever and pruritis are common. Laboratory abnormalities such as circulating immune complexes and hemolytic anemia are also seen.

Pathology: Lymph nodes involved by AITL show architectural effacement by a proliferation of small- to intermediate-sized lymphocytes with pale to clear cytoplasm and variable numbers of large transformed cells.92 Regressively transformed germinal centers are often present and there is a characteristic proliferation of arborizing vessels (Figure 52.18). Increased numbers of follicular dendritic cells are characteristic of AITL, often associated with the vascular proliferation.

Immunophenotype: The malignant cells are typically CD4+, and recent studies have shown most cases of AITL to coexpress CD10.93 94 Expression of other T-cell antigens is variable. Most cases also display scattered large, EBV-positive B-cells that may give rise to secondary B-cell lymphomas in a subset of patients.

Molecular genetics: Clonal T-cell rearrangements are detectable by PCR or Southern blot studies in at least 75% of cases. Clonal B-cell populations may also be detected in some cases, likely corresponding to accompanying EBV-positive B-cells.91 Recurring cytogenetic abnormalities include trisomy 3, trisomy 5, and gains

Figure 52.18 Angioimmunoblastic T-cell Lymphoma. The lymph node is effaced by a diffuse proliferation of intermediate to large lymphocytes with pale cytoplasm. There is an accompanying vascular proliferation

of the X chromosome, although none of these represent specific findings.95

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