Residual Germinal Centers Blending with Extra-Nodal Marginal Zone Lymphoma: Don’t Confuse it with Large Cell Transformation

Lessons From the Friday Unknowns

The neoplastic monocytoid lymphocytes are positive for CD20 and CD43

CD3 stain (left) | CD20 stain (middle) | CD43 stain (right)

Residual germinal centers are seen abutting epithelial islands invaded and surrounded by neoplastic monocytoid cells.

EI: Epithelial Islands; MC: Monocytoid Cells; GC: Germinal Centers

Some residual follicles get overrun by the lymphoma component, as shown below. In these cases, it might be challenging to recognize that the large centroblasts belong to benign follicles, as they blend with the lymphomatous component.

Performing immunohistochemical stains in these cases such as BCL2 (negative ), CD10 (positive), BCL6 (positive), and Ki67 (high) is helpful to distinguish residual follicles from extra-nodal marginal zone lymphoma in large cell transformation.

Link to digital slide | Slides labeled case 1: bit.ly/35E2mNT

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Siba El Hussein, MD

Hematopathology | Cytopathology | Molecular pathology | Digital pathology | Data science | Machine learning