The Evolution of <i>Pneumocystis jirovecii</i> Pneumonia Prophylaxis for Pediatric Patients With Extracranial Solid Tumors: A Review of Historical Insights and Future Directions

Pneumocystis jirovecii pneumonia (PJP) remains a modern-day complication for pediatric patients receiving treatment for extracranial solid tumors (ST), highlighting the need for reconsideration of our current approach toward PJP prophylaxis. This critical review aims to evaluate both universal and risk-stratified approaches to PJP prophylaxis for pediatric patients with ST. It traces the evolution of prophylaxis strategies over the past six decades, with examination of trends in PJP incidence, fatality, risk factors (including those posed by novel therapeutics), prophylaxis efficacy and safety, international prophylaxis guidelines, and guideline implementation into clinical practice. Although compliant use of prophylaxis effectively prevents PJP, our understanding of specific risk factors and prophylaxis-related toxicity has predominantly been established for pediatric patients with hematological rather than ST. This complicates our assessment of the risks and benefits of PJP prophylaxis for those with ST, resulting in variations in prophylaxis guidance and practices, and is further compounded by increased use of novel immunomodulating agents. These knowledge gaps make it difficult to reliably inform a risk-stratified approach to PJP prophylaxis in pediatric patients with extracranial ST. Further longitudinal research and implementation strategies are required to support the development of effective, standardized PJP prophylaxis practices.