Pembrolizumab for refractory primary mediastinal B-cell lymphoma with central nervous system involvement.

Primary mediastinal large B-cell lymphoma (PMBCL) is a rare aggressive B-cell lymphoma characterized by the frequent presence of amplification and translocation events at 9p24.1, resulting in the expression of the programmed cell death-1 (PD-1) ligands PD-L1 and PD-L2. Pembrolizumab, a humanized anti-PD-1 monoclonal antibody, binds PD-1 and blocks this interaction, enhancing the activity of the immune system against tumor cells, and has shown activity in PMBCL and in some cases of primary and secondary central nervous system (CNS) lymphoma. We report the case of a 40-year-old woman diagnosed with relapsed PMBCL and secondary CNS involvement who responded to pembrolizumab monotherapy, allowing for a later allogeneic stem cell transplant.