An Usual Presentation of Pneumocystis jirovecii Pneumonia in a Woman Treated With Immune Checkpoint Inhibitor.

We describe a case of Pneumocystis jirovecii pneumonia in an 18-year-old female individual with refractory primary mediastinal B-cell lymphoma treated with the immune checkpoint inhibitor pembrolizumab. She received 11 doses of pembrolizumab without immune-related adverse events (irAEs) before the diagnosis of P. jirovecii pneumonia. However, prophylactic trimethoprim/sulfamethoxazole was discontinued 6 months of postautologous stem cell transplant per standard guidelines. This case report highlights the importance of judicious infectious disease evaluation while on immune checkpoint inhibitor therapy as symptoms can often mimic irAEs. Furthermore, the benefits of immunosuppressive therapy for the treatment of presumptive irAEs must be weighed against the possible increased risk for opportunistic infections.