Utility of bronchoalveolar lavage in checkpoint inhibitor pneumonitis evaluation: a narrative review.

Background and Objective: Checkpoint inhibitors have revolutionised cancer treatment over the past few decades; however, their successes in clinical trials and real-world settings have been tempered by immune-related adverse events (IrAEs). Checkpoint inhibitor pneumonitis (CIP), the leading cause of IrAE-related mortality, poses a significant challenge to clinicians due to non-specific clinical features and unpredictable disease trajectory. Bronchoalveolar lavage (BAL) is a diagnostic procedure that offers insight into the immune and molecular processes underlying CIP. This review presents the current role and application of BAL in the evaluation of CIP, explores current literature, and discusses how recent advances in research and technology may shape future approaches to its diagnosis and management. Methods: A comprehensive literature search using PubMed, EMBASE, and Cochrane databases was performed to identify recent literature evaluating BAL findings in CIP. This review synthesizes findings from these studies to provide an up to date and comprehensive overview of the role of BAL in CIP management. Key Content and Findings: Current guidelines recommend BAL in symptomatic patients when the diagnosis of CIP remains uncertain, primarily to exclude infection and other disease processes. However, the unpredictable clinical course of CIP narrows the window of opportunity to safely perform BAL. Variable utilisation of BAL in clinical practice may also be attributed to the lack of clinically reliable and applicable biomarkers that could improve diagnostic clarity. Beyond lymphocytosis, a well-recognised finding in BALs of patients with CIP, the role of specific immune cell populations and molecular drivers in shaping a proinflammatory microenvironment has been highlighted in multiple emerging studies. Advances in molecular profiling, immunogenomics, and lung microbiome research hold promise for enhancing our understanding of CIP pathogenesis and guiding future approaches to its diagnosis and management. Conclusions: In current clinical practice, BAL remains an important investigation to support a diagnosis of CIP; however, its diagnostic value remains uncertain. Enhanced understanding of the CIP immune landscape is fundamental to identifying robust diagnostic and predictive biomarkers that could improve diagnosis and patient outcomes in cancer patients treated with checkpoint inhibitors.