A rare phenotype of peripheral T-cell lymphoma, NOS: coexpression of CD15, CD20, and T follicular helper markers in a DUSP22^alt case Free

A 73-year-old woman, previously diagnosed with peripheral T-cell lymphoma (PTCL), presented with groin lymphadenopathy. Biopsy showed effaced architecture with pleomorphic intermediate to large lymphoid cells (panel A, 40× objective; panel B, 100× objective, hematoxylin and eosin [H&E] stain). Immunophenotyping revealed diffuse expression of CD2, CD3 (panel C, 40× objective), CD4, CD5, CD20 (panel D, 40× objective), CD30 (panel E, 40× objective), CD15 (panel F, 40× objective), BCL6 (panel G, 40× objective), ICOS (CD278) (panel H, 40× objective), PD-1 (CD279) (panel I, 40× objective), IRF4/MUM1 (panel J, 40× objective) and was negative for CD7, CD8, CD10, ALK-1 (panel K, 40× objective), T-cell cytotoxic markers, CD79a, PAX5, and EBER. Fluorescence in situ hybridization confirmed IRF4/DUSP22 gain in 37 of 200 nuclei (panel L, ZytoLight SPEC IRF4, DUSP22 Dual Color Break Apart Probe, ≥3 fusions), leading to a diagnosis of PTCL not otherwise specified (NOS) with DUSP22^alt.

This case uniquely demonstrates coexpression of T follicular helper (TFH) markers, CD30, CD15, and CD20, an uncommon immunophenotype in PTCL-NOS, posing diagnostic challenges and potential misclassification as other T-cell or B-cell lymphomas. As DUSP22 inhibits T-cell activation, its gain may explain aberrant PD-1 and ICOS expression, biomarkers associated with T-cell activation pathways. The presence of TFH markers in DUSP22^alt PTCL expands its known immunophenotypic spectrum, emphasizing the importance of comprehensive immunophenotyping and cytogenetics for accurate diagnosis.

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