T cell and NK cell lymphoid proliferations

Question 1

AITL - nodal TFH cell lymphoma, angioimmunoblastic type

Answer 1

Neoplasm of mature T-cells with a T-follicular helper phenotype, systemic disease and a lymphoid infiltrate with prominent proliferation of high endothelial venules (HEVs) and follicular dendritic cells (FDCs)

Question 2

AITL - diagnosis

Answer 2

Essential
- Nodal disease
- **CD4+, CD8- **negative atypical lymphoid cells (occasionally CD4-)
- Extrafollicular FDC (follicular dendritic cell) expansion and **HEV (high endothelial venule) hyperplasia **(mild in tumour cell-rich cases)

Desirable
- Expression of **≥1 TFH markers, including strong PD1 **
- **Clonal TCR gene **rearrangement and/or mutation involving **RHOA p.G17V or IDH2 p.R172 **
- EBV positive B cells

Question 3

Clinical presentation of AITL

Answer 3

• M>F, elderly/middle aged patients
• Constitutional symptoms and LAD
• BM involved in 70% cases
• Pruritic maculopapular rash is common
• Immune dysregulation –> warm Abs, cold aggs, thrombocytopenia, positive RF, cryoglobulinaemia
• Eosinophilia, lymphopenia, plasma clls and neutrophilia can be seen

Question 4

Histopathology of AITL

Answer 4

Nodular infilitrate
Background reactive lymphocytes, plasma cells, histiocytes and eosinophils

Question 5

IHC and flow in AITL

Answer 5

Pan-T cell antigens CD2+ 3+ 5+
Variable loss of CD7-
Dim sCD3+

Nearly always CD4+ and CD8-

TFH markers are positive:
PD1 (CD279)
ICOS
BCL6
CXCL13
CD10

Detection of an abnormal CD4+/CD10+ or CD4+/PD1+br T cell population on flow or IHC may help diagnosis

Immunostains for CD21, CD23 and CD35 highlight the characteristic **extrafollicular follicular dendritic cell meshworks that encircle high endothelial venules **

B-immunoblasts are highlighted by CD20; EBERish is positive in 80% of cases

Question 6

Molecular in AITL

Answer 6

• RHOA
• IDH2
• other assoc mutations which can confer poor prognosis, DNMT3a and TET2