The lung transplant endobronchial biopsy: a forgotten specimen comes of age.

Mucosal or endobronchial biopsies (EBB) are typically used in the diagnosis of directly visualized bronchial lesions, infection, and sarcoidosis, but their utility in the evaluation of lung transplant recipients is controversial. EBB represents an attractive alternative to transbronchial biopsy (TBB): EBB provides straightforward sampling of airway pathology with decreased complication rates due to minimal and visualizable bleeding and the elimination of pneumothorax risk. In lung transplant recipients, EBB may be obtained when TBB is too high-risk, including in the setting of acute lung allograft dysfunction (ALAD) requiring mechanical ventilation or in advanced chronic lung allograft dysfunction (CLAD). Most centers do not include EBB in post-transplant surveillance or for-cause bronchoscopy protocols, possibly due to a lack of a common histologic interpretation system. Previous work has demonstrated that lymphocytic inflammation in lung transplant EBB is associated with acute cellular rejection and future risk for CLAD, but these have not translated into subsequent studies on clinical utility or into clinical practice. Recent multicenter studies suggest that gene expression-based diagnostics leveraging EBB may outperform histologic grading and provide important prognostic utility in predicting graft loss. Herein, we will review what is known about the lung transplant mucosa including recent diagnostic advances and propose how EBB analyses could be incorporated into research studies and clinical workflows. We propose that mucosal sampling could provide safe, consistent, and informative data to improve patient outcomes after lung transplant.