21. Peripheral T-cell lymphoma with follicular pattern: a ‘real’ entity

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Peripheral T-cell lymphoma (PTCL) with a follicular pattern of growth is a rare condition with a few cases described in the literature. According to the World Health Organization classification, cases of PTCL with a follicular pattern are included in the category of unspecified PTCL. We report a case of PTCL with a prominent bilateral inguinal lymphadenopathy from a 71-year-old man. Microscopic examination of the lymph node identified effacement of the nodal architecture by a nodular, follicular infiltrate extending across the capsule. The follicular compartment was composed of a mixture of cells including small lymphocytes, and small and large lymphoid cells with round or irregular hyper-chromatic nuclei resembling centrocytes, centroblasts and immunoblasts. Immunohistochemical stains revealed that the follicles contained mostly T-cell type cells with co expression of CD3, CD4 and CD5. This was also confirmed by flow cytometry showing the most of the cells to be CD4 positive T cells. The Ki67 indicated a proliferation index around 10%. CD20 staining showed residual B-cells within the follicular areas suggesting that the tumour had colonised lymphoid follicles. Molecular studies confirmed a monoclonal T-cell receptor γ gene rearrangement. The bone marrow aspiration and biopsy were unremarkable. This case demonstrates the importance of considering the diagnosis of PTCL in lesions with a nodular pattern of growth, particularly in view of the different prognostic features and treatment modalities for T-cell and B-cell neoplasms.