Table 2.
Common Markers Used for Diagnosis of AITL
| Markers | Utility | Comment |
|---|---|---|
| CD20 and PAX5 | Identify B-cell follicles, the distribution, proportion, and cytologic features of B cells in the infiltrate | B immunoblasts and HRS-like cells are variably positive for CD20 and PAX5 |
| CD3 | Access the distribution, proportion, and cytologic features of T cells in the infiltrate; identify T cells with cytologic atypia and/or altered expression of pan–T-cell antigens | Dim expression or loss of surface CD3 is found in a subset of AITL |
| CD2, CD5, and CD7 | Identify T cells with cytologic atypia and/or altered expression of pan–T-cell antigens | Loss of CD7 is common in AITL |
| CD4 and CD8 | Access the distribution, proportion, and cytologic features of T-cell subsets | Atypical T cells are CD4+ in >90% of AITLs |
| CD21 and CD23 | Identify FDC meshworks underlying follicles and extrafollicular proliferation of FDC meshworks, usually around HEVs | CD21 is generally more sensitive than CD23 |
| CD10 | Highlight reactive germinal centers; help identify atypical T cells with a TFH phenotype | Less sensitive but more specific. CD10 is often weak, heterogeneous, and confined to a small subset of the atypical T cells |
| BCL6 | Highlight reactive germinal centers; help identify atypical T cells with a TFH phenotype | Less sensitive but more specific |
| PD1 | Help identify atypical T cells with a TFH phenotype | Very sensitive but less specific; strong PD1 is more specific than weak staining |
| ICOS | Help identify atypical T cells with a TFH phenotype | Very sensitive (>90% sensitivity) but less specific |
| CXCL13 | Help identify atypical T cells with a TFH phenotype | Less sensitive but more specific; cytoplasmic staining with a perinuclear dot pattern |
| CD30 | Highlight B immunoblasts and HRS-like cells; may highlight a subset of the atypical T cells | CD30+ atypical T cells can be found in 20% to 30% of AITLs |
| κ and λ | Evaluate for light chain restriction in plasma cells | Polytypic plasmacytosis is common; monotypic plasma cells can be found in rare cases |
| EBV ISH | Identify EBV-positive B blasts | Varying numbers of EBV-positive cells can be found in 80% to 90% of AITLs |
AITL, angioimmunoblastic T-cell lymphoma; EBV, Epstein-Barr virus; FDC, follicular dendritic cell; HEV, high endothelial venule; HRS, Hodgkin/Reed-Sternberg; ISH, in situ hybridization; TFH, T follicular helper.