Primary cutaneous CD4+ small/medium T-cell lymphoproliferative disorder-clinical and histopathologic features, differential diagnosis, and treatment.

Primary cutaneous CD4+ small/medium T-cell lymphoproliferative disorder usually presents as a slow-growing and asymptomatic solitary lesion in the form of a nodule or tumor in the head and neck region. By definition, it is histologically characterized by small- to medium-sized CD4+ lymphocytes involving the dermis in a dense and either nodular or diffuse pattern. Epidermotropism should be absent or minimal. Tumor cells are accompanied by numerous reactive B cells, plasma cells, histiocytes, and eosinophils. This lymphoproliferative disorder is characterized by the expression of follicular helper T-cell markers, particularly B-cell lymphoma 6 (BCL-6), programmed cell death protein 1 (PD-1), and C-X-C motif chemokine ligand 13 (CXCL-13), while CD10 is usually negative. Molecular studies show a clonal rearrangement of T-cell receptor genes in more than 60% of cases. Management of disease includes surgical excision, radiation therapy, and steroids (topical or intralesional). Patients with this diagnosis have an excellent prognosis, with a clinical course that is invariably indolent.