Pneumocystis jirovecii Pneumonia in Adults with Brain Tumors: Treatment-Related Risk, Diagnostic Challenges, and Evidence-Informed Prophylaxis—A Narrative Review

Pneumocystis jirovecii pneumonia (PJP) is an opportunistic infection increasingly recognized in patients without human immunodeficiency virus (HIV) who receive immunosuppressive therapy. Patients with brain tumors may be vulnerable because of prolonged corticosteroid exposure, temozolomide-based chemoradiotherapy, and rituximab-based regimens. This narrative review summarizes current evidence on therapy-associated PJP in adults with brain tumors, emphasizing risk identification, diagnosis, prophylaxis, and management. A targeted PubMed search through 1 August 2026 was supplemented by reference-list screening, regulatory documents, and relevant clinical guidelines; brain-tumor-specific evidence was prioritized, with selective extrapolation from other non-HIV immunocompromised populations. High-dose or prolonged corticosteroid use, concurrent temozolomide and radiotherapy, and rituximab-based regimens, particularly in primary central nervous system lymphoma, were repeatedly identified as clinically relevant contributors to PJP risk. Contemporary studies suggest an average incidence below 1% during temozolomide chemoradiotherapy, although risk is heterogeneous and may increase with corticosteroid exposure, lymphopenia, and combined immunosuppression. PJP in patients without HIV generally has a more acute course and higher mortality than HIV-associated disease, and trimethoprim-sulfamethoxazole remains the first-line agent for prophylaxis and treatment. Early identification of high-risk patients and timely prophylaxis are important components of supportive neuro-oncology care.