Programmed death-1 expression in cutaneous B-cell lymphoma.

Background Numbers of programmed death-1 (PD-1) positive T cells have prognostic significance in some types of nodal B-cell lymphomas, but data on PD-1 expression in cutaneous B-cell lymphoma (CBCL) are few. In this study we determined the expression and distribution of PD-1 on neoplastic B cells and reactive T cells in skin sections from primary CBCLs. Methods By means of immunohistochemical staining, PD-1 expression was investigated in skin biopsies from 10 patients with primary cutaneous marginal zone lymphoma (PCMZL), 18 patients with primary cutaneous follicle center lymphoma (PCFCL) and 12 patients with primary cutaneous diffuse large B-cell lymphoma–leg type (PCDLBCL–LT). Results Neoplastic B cells were negative for PD-1 in all cases, except for two cases of PCDLBCL–LT. The frequency of PD-1+ T cells was significantly higher in PCFCL than in PCMZL and PCDLBCL–LT, accounting for 20, 10 and 3% of the total number of infiltrating cells, and 60, 20 and 15% of the total number of CD3+ T cells, respectively. Conclusions PD-1 is rarely expressed by the neoplastic B cells in CBCL. High percentages of PD-1+ T cells, particularly if found outside germinal centers, support a diagnosis of PCFCL.