S/no. | Diagnostic points and pitfalls |
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1. | The presence of a prominent PD-1-positive T cell infiltrate and expanded FDC meshworks in NLPHL may raise the possibility of AITL. However, their pattern of FDC meshworks is distinct and AITL shows a polymorphic background cellular population. |
2. | In NLPHL, where the LP cells are usually CD30 and EBV negative, there may be non-neoplastic activated cells/immunoblasts that may be strongly positive for CD30 and occasionally positive for EBV on EBER-ISH. If attention is not paid to the type of cells expressing CD30 and EBER (ie, neoplastic vs bystander cells), the pathologist may misdiagnose NLPHL as CHL. |
3. | Patients with recurrent NLPHL may have previously received anti-CD20 therapy that may lead to loss of CD20 expression in the LP cells. This should not be considered as inherent CD20 absence favouring CHL. |
4. | Oct-2 is a highly sensitive immunohistochemical marker for the LP cells in NLPHL and can be helpful as a reference marker in localising the LP cells for comparison with other immunohistochemistry stains. |
5. | NLPHL can have a diffuse T cell-rich pattern, which may predominate. This diffuse pattern is especially common in recurrences and bone marrow involvement. In a small biopsy or bone marrow sample, this can be indistinguishable from TCHRLBCL as the large cells are morphologically and immunohistochemically similar. The pathologist should be cautious in making a diagnosis of de novo TCHRLBCL in such specimens, especially when there is no antecedent history of TCHRLBCL and/or the clinical picture is atypical for TCHRLBCL (eg, localised disease). |
6. | In NLPHL with a predominant diffuse T cell-rich pattern, generous sampling and immunohistochemistry across multiple sections to identify FDC meshworks and B cell-rich nodules may be required as these may be very focal. |
7. | In a biopsy morphologically consistent with TCHRLBCL, correlation with clinical history is important. If a history of NLPHL is present, classification as ‘TCHRLBCL-like transformation’ of NLPHL rather than de novo TCHRLBCL is appropriate. |
AITL, angioimmunoblastic T cell lymphoma; CHL, classical Hodgkin lymphoma; EBER-ISH, Epstein-Barr virus by in situ hybridisation for EBER; EBV, Epstein-Barr virus; FDC, follicular dendritic cell; LP, lymphocyte-predominant; TCHRLBCL, T cell/histiocyte-rich large B cell lymphoma.