Clinical heterogeneity of primary cutaneous γδ T-cell lymphoma: a 20-year single-institution experience

Primary cutaneous γδ T-cell lymphoma (PCGDTCL) is a rare cutaneous T-cell lymphoma defined by γδ T-cell receptor expression and a cytotoxic phenotype. It has historically been considered highly aggressive, with median survival of 15-30 months and no standardized treatment due to its rarity. However, emerging reports describe subsets with relatively indolent behavior. We report a 20-year single-institution experience to better define the clinical spectrum and therapeutic implications of PCGDTCL.

Patients diagnosed with PCGDTCL at Samsung Medical Center between January 2005 and September 2025 were retrospectively reviewed. Clinical, pathologic, and immunophenotypic features were collected and confirmed by hematopathology review. Pathologic features were visualized using heatmaps, and treatment courses were visualized using swimmer plots. Tumor response was evaluated according to Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1.

Six patients were identified (median age 57 years). All presented with cutaneous lesions, ranging from localized solitary lesions to multifocal cutaneous involvement. ^18F-fluorodeoxyglucose positron emission tomography (FDG-PET) demonstrated heterogeneous metabolic activity, with maximum standardized uptake values (SUVmax) ranging from absent uptake to 8.9. Immunophenotyping showed uniform CD3 positivity, T-cell receptor γδ expression, βF1 negativity, and variable CD4, CD8, and CD56 expression. First-line therapies included observation, corticosteroids, CHOP (cyclophosphamide, doxorubicin, vincristine, prednisone), and GDP (gemcitabine, dexamethasone, cisplatin). Durable complete remissions occurred with CHOP and GDP. One patient experienced multiple relapses, later developed clinicopathologic features resembling mycosis fungoides, and survived for 13 years.

PCGDTCL appears to show broader clinical and therapeutic heterogeneity than historically appreciated. Durable responses in selected patients suggest that treatment responsiveness may vary across the disease spectrum.