Pneumocystis jirovecii Pneumonia Secondary to Blinatumomab Therapy: A Case Report.

Introduction: With the increasing use of blinatumomab in relapsed or refractory B-cell precursor acute lymphoblastic leukemia (ALL), including minimal residual disease (MRD)-positive cases, awareness of its adverse effects has gradually improved. Pneumocystis jirovecii pneumonia (PCP) associated with blinatumomab therapy is rare.

Case Presentation: We present a case of PCP in a patient undergoing blinatumomab therapy. A 70-year-old female diagnosed with Philadelphia-like CRLF2 overexpression B-cell precursor ALL received blinatumomab as consolidation therapy after achieving complete remission with prior induction chemotherapy. On the second day of blinatumomab infusion, she developed intermittent low-grade fever, and chest computed tomography (CT) revealed subtle infiltrates and nodules. Despite empiric trimethoprim-sulfamethoxazole (TMP-SMX) prophylaxis, she progressed to significant shortness of breath and type I respiratory failure, with increased lactate dehydrogenase and β-D-glucan assays. Chest CT showed diffuse ground-glass opacities with scattered small nodules. The dry cough prompted next-generation sequencing of peripheral blood, which tested positive for pneumocystis jirovecii without evidence of other pathogens. Consequently, the patient was diagnosed with PCP. The first cycle of blinatumomab had to be discontinued, and therapeutic dosages of TMP-SMX and dexamethasone were administered, resulting in full recovery and stable condition during follow-ups.

Conclusion: PCP is rare in B-cell precursor ALL patients receiving blinatumomab therapy but manifests with early onset and rapid disease progression. Despite prophylaxis, PCP infection cannot be ignored during blinatumomab therapy. Therefore, heightened attention is warranted when using blinatumomab therapy.