Track

Abstract

The 5th edition of the World Health Organization classification of hematolymphoid tumors (WHO-HAEM5) reclassifies the rare entity previously known as primary cutaneous follicular helper T-cell lymphoma to primary cutaneous peripheral T-cell lymphoma, not otherwise specified – follicular helper T-cell phenotype (pcPTCL, NOS – FHT). We report a case of an 83-year-old man who presented initially with erythematous papules that slowly progressed to multiple violaceous, mobile subcutaneous nodules and tumors on his arms and legs. There was no history of mycosis fungoides and no clinical evidence of systemic disease at time of presentation. A series of biopsies demonstrated an atypical lymphoid infiltrate evolving from a B-cell rich process to an obvious proliferation of cytologically atypical medium-sized T-cells. Immunohistochemical staining demonstrated tumor cells positive for CD3, CD4, and T-follicular helper cell markers PD-1, ICOS, and BCL6. In the context of the patient’s clinical presentation, the histologic and immunophenotypic findings supported a diagnosis of pcPTCL, NOS – FHT phenotype. This case highlights the diagnostic challenges posed by this uncommon entity, particularly its potential to mimic a primary cutaneous B-cell lymphoma histopathologically. Recognition of its defining immunophenotypic features and integration with clinical findings are essential for accurate classification and appropriate management. We revisit this rare cutaneous T-cell lymphoma subtype within the framework of the updated WHO-HAEM5 classification, emphasizing the evolving understanding of its pathogenesis and the need for heightened awareness among dermatopathologists.