Secondary Cutaneous Dissemination of Peripheral T-Cell Lymphoma With T-Follicular Helper Phenotype as a Patient's Fourth Primary Malignancy.

Peripheral T-cell lymphomas expressing follicular helper T-cell (TFH) markers have recently been identified. Although this type of lymphomas consist of malignant proliferation of T-cells, they may also exhibit B-cell clonality. We report a case of a 72-year-old woman with multiple erythematous to violaceous nonscaling plaques and tumors on her trunk. Histopathological analysis revealed a dense infiltration of medium-to-large-sized atypical cells throughout the entire dermis. The result of immunohistochemical analysis showed that the infiltrating T-cells expressed programmed death-1 (PD-1), CD10, Bcl-6, CD3, CD4, CD2, and CD5. The infiltrate also contained scattered atypical large B-cells. Based on the clinical appearance and the histopathological findings, we diagnosed the patient with secondary cutaneous dissemination of peripheral T-cell lymphoma with expression of a T-follicular helper phenotype.