Coexisting Angioimmunoblastic T-Cell Lymphoma and Chronic Lymphocytic Leukemia/ Small Lymphocytic Lymphoma

Lessons From the Friday Unknowns

Histologic sections shows almost complete replacement of lymph node by lymphoma extending into perinodal tissue.

The neoplasm is composed of small and intermediate-size with irregular nuclear contours, associated with plasma cells and eosinophils.

Immunohistochemical studies performed on the specimen revealed that the neoplastic cells are of T-cell lineage, positive for CD3, CD5, PD-1, CXCL13, Bcl-2 (weak) and a subset of these cells are positive Bcl-6, and c-Myc (20–30%, weak). The neoplastic T-cells are negative for CD10, CD15, CD20, CD21, CD57, Pax-5 and cyclin D1.

The antibody specific for CD21 highlights irregular networks of follicular dendritic cells.

Reactive plasma cells in the lymph node express kappa and lambda light chains. Lymphocytes are negative for light chains.

The CD20, CD30 and Pax-5 antibodies highlight increased B-cells within the T-cell population; some of these B-cells are large.

In the areas of lymph node that are incompletely replaced by these cells, small lymphocytes are increased in the subcapsular region. These lymphocytes represent 5–10% of the lymph node.

The small lymphocytes in the subcapsular zone of the lymph node are positive for CD5 (dim), CD20 and Pax-5, and are negative for CD3, CD10, CD15, CD21, CD57 and cyclin D1.

CD5 stain highlighting subcapsular CLL cells and adjacent AITL cells
CD20 stain highlighting subcapsular CLL cells

Epstein-Barr virus encoded RNA (EBER) was performed on a paraffin-embedded tissue block. Many plasma cells and B-cells intermixed within the neoplasm are positive for EBER.

Flow cytometry immunophenotypic studies showed an aberrant population of B-cells representing 40% of events expressing for monotypic kappa, CD5, CD19, CD20, CD22 (partial) and CD23, and negative for FMC7.

In summary, the predominant neoplasm in this biopsy specimen is best classified as angioimmunoblastic T-cell lymphoma. In addition, the small B-cells in the subcapsular region are suggestive of coexistent chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL). This suggestion is supported by the results of the flow cytometry immunophenotypic results. It may be helpful to assess the complete blood count and differential count for lymphocytosis in this case. In addition, bone marrow evaluation may be helpful to assess for involvement by either T-cell lymphoma or CLL/SLL.

Link to digital slides: https://bit.ly/3pMyXtB | Slides labeled case 4

Suggested Read: https://bit.ly/3iBAP6I

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