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Evaluation of primary mediastinal large B cell lymphoma by flow cytometry
Sindhu Cherian1, Jonathan R Fromm1
1Department of Laboratory Medicine, University of Washington, Seattle, Washington.
Insights
Flow cytometry effectively identifies primary mediastinal large B cell lymphoma (PMLBCL) cells. A classical Hodgkin lymphoma assay is superior to a B-NHL assay for PMLBCL detection, revealing a distinct CD8+ T cell infiltrate.
Area of Science:
- Hematology
- Immunology
- Oncology
Background:
- Primary mediastinal large B cell lymphoma (PMLBCL) shares characteristics with classical Hodgkin lymphoma (CHL).
- Understanding the neoplastic and reactive cellular components of PMLBCL is crucial for accurate diagnosis and treatment.
- Flow cytometry (FC) is a valuable tool for immunophenotypic analysis of lymphomas.
Purpose of the Study:
- To evaluate the utility of flow cytometry in characterizing the neoplastic and reactive cellular infiltrate in PMLBCL.
- To compare the effectiveness of B-cell non-Hodgkin lymphoma (B-NHL) and CHL assays for PMLBCL detection using FC.
- To identify unique immunophenotypic features of neoplastic and reactive cells in PMLBCL.
Main Methods:
- Retrospective analysis of 24 PMLBCL cases using flow cytometry.
- Application of FC combinations designed for B-NHL, T-NHL, and CHL detection.
- Detailed immunophenotypic characterization of neoplastic and reactive cell populations.
Main Results:
- The CHL assay successfully identified the neoplastic population in all PMLBCL cases, outperforming the B-NHL assay (18/24 cases).
- Neoplastic PMLBCL cells exhibited a B cell immunophenotype (CD19/CD20+, bright CD40+) with frequent CD30 expression and variable CD10/CD15 negativity.
- A prominent CD8+ T cell infiltrate was observed in PMLBCL, with lower CD4/CD8 ratios compared to reactive tissues and CHL.
Conclusions:
- Flow cytometry is effective for detecting the neoplastic cells of PMLBCL.
- A CHL-specific FC assay demonstrates superior performance for PMLBCL identification compared to a standard B-NHL assay.
- PMLBCL is characterized by a distinct B cell immunophenotype and a unique reactive T cell infiltrate, notably a CD8+ T cell predominance.
Background:
Primary mediastinal large B cell lymphoma (PMLBCL) is a B cell non-Hodgkin lymphoma (B-NHL) that shows morphologic, immunophenotypic, and genetic similarities to classical Hodgkin lymphoma (CHL). We evaluated the neoplastic and reactive infiltrate of PMLBCL by flow cytometry (FC).
Methods:
A total of 24 cases of PMLBCL were retrospectively characterized using FC combinations for B-NHL, T-NHL, and CHL.
Results:
The CHL assay identified the neoplastic population (NP) in all cases, while the B-NHL assay identified the NP in 18 of 24 cases. In four cases, the neoplastic population was retrospectively identified in the B-NHL tube, given the CHL tube-derived immunophenotype. Neoplastic cells of PMLBCL displayed a B cell immunophenotype (CD19/CD20+ ), with CD40 consistently and brightly expressed. Most cases lacked immunoglobulin light chains, CD10, and CD15; CD30 was frequently expressed. All cases showed expression of CD71 and CD95. The reactive infiltrate in PMLBCL showed increases in T cells relative to reactive tissues. Lower CD4/CD8 ratios in PMLBCL relative to CHL and reactive tissues were also observed. Although not seen as commonly as with CHL, 41% of cases showed a reactive CD3/CD4/CD7bright /CD45bright+ T cell population. Reactive populations seen in PMLBCL were similar to that seen in diffuse large B cell lymphoma, not otherwise specified.
Conclusions:
FC can detect the NP of PMLBCL and a FC assay for CHL performed better than a B-NHL assay in this regard. The neoplastic cells showed a B cell immunophenotype with over-expression of CD40. The reactive infiltrate in PMLBCL shows unique features including a prominent CD8+ T cell infiltrate. © 2017 International Clinical Cytometry Society.
