Primary cutaneous T-cell lymphoma expressing FOXP3: A case report supporting the existence of malignancies of regulatory T cells

Regulatory T (Treg) cells, which represent 5% to 10% of peripheral T cells, regulate the activities of T-cell subsets by performing immunosuppressive functions and thus preventing the development of autoimmune responses. The majority of Treg cells are CD4(+), CD25(+), and FOXP3(+). Recently, it has been demonstrated that the tumor cells in adult T-cell leukemia lymphomas can function as Treg, raising the question of whether any variant of primary Cutaneous T-cell lymphoma may also express a regulatory phenotype. We describe an extraordinary case of primary Cutaneous T-cell lymphoma clinically characterized by protean Cutaneous manifestations and histologically showing a pattern consistent with epidermotropic pleomorphic medium/large-cell primary cutaneous T-cell lymphoma. The majority of neoplastic cells were CD4(+) CD25(+) T cells and strongly expressed FOXP3. With this background, the Current case, characterized by an aggressive Course requiring polychemotherapy, may support the existence of lymphoproliferative malignancies of Treg cells. (J Am Acad Dermatol 2009-61:348-55.)