Distinguishing angioimmunoblastic T-cell lymphoma from peripheral T-cell lymphoma, unspecified, using morphology, immunophenotype and molecular genetics.

To identify distinguishing histological, immunophenotypic and molecular genetic features between angioimmunoblastic T-cell lymphoma (AITL) and peripheral T-cell lymphoma (PTL). Nodal T-cell lymphomas examined (n =137), included AITL (n = 89), PTL (n = 22), anaplastic large cell lymphoma (n = 16) and 'AITL/PTL indeterminate' (n = 10) with overlapping features between AITL and PTL, showing morphology typical of AITL but lacking follicular dendritic cell expansion. Immunohistochemistry for CD3, CD20, CD21 and CD10, in situ hybridization for Epstein-Barr virus encoded RNA (EBER) and polymerase chain reaction for T-cell and B-cell clonality analysis were performed. Of the AITLs, 74/89 showed typical morphology, whereas 15/89 showed hyperplastic follicles. AITL and 'AITL/PTL indeterminate' showed a polymorphous infiltrate and prominent vascularity in all cases. In both groups, CD10 was present in the majority and clear cells and EBER positivity were specific (but not universal) features lacking in PTL. Detection of T-cell clonality was significantly higher in AITL (90%) compared with PTLu (59%). Clear cells and EBV infection (when present) are useful distinguishing features and CD10 a sensitive and specific marker of AITL. Hyperplastic follicles are present in a significant minority of AITL. AITL/PTL indeterminate probably falls within the spectrum of AITL rather than PTL.