Case Report: Diagnostic utility of pleural tissue debris retrieved during percutaneous drainage for the diagnosis of malignant pleural effusion and molecular profiling.

Background: Although pleural tissue debris is occasionally encountered in the drainage systems of patients undergoing catheter or chest tube drainage, its clinical utility has not been reported. Here, we report two cases in which pleural tissue debris retrieved during catheter drainage enabled a definitive diagnosis of malignant pleural effusion (MPE) and molecularly guided treatment decisions. Case presentation: The first case involved a 67-year-old woman with rheumatoid arthritis-associated interstitial lung disease who developed a right pleural effusion suggestive of lung cancer with pleural metastasis. Invasive procedures for tissue acquisition were required; however, biopsy was withheld because of the high risk of pneumothorax and acute exacerbation of the underlying lung disease. Tissue debris was incidentally found in the drainage system. The tissue was adequate for pathological examination and revealed lung squamous cell carcinoma without genomic alterations. Chemoimmunotherapy was initiated without further invasive procedures. The second case involved a 78-year-old woman who presented with a left pleural effusion and a brain lesion, highly suggestive of lung cancer with brain metastasis. She declined invasive diagnostic procedures; however, tissue debris was incidentally collected from the drainage bottle and diagnosed as lung adenocarcinoma. Molecular testing revealed that the tumor harbored an epidermal growth factor receptor (EGFR) L858R mutation, allowing first-line targeted therapy to be initiated without further invasive testing. Conclusion: To the best of our knowledge, this is the first case report to describe the clinical utility of pleural tissue debris for the diagnosis of MPE and its suitability for molecular profiling. Our report highlights that this previously overlooked byproduct of routine pleural drainage can provide adequate material for histopathological diagnosis, immunohistochemistry, and molecular testing in patients with MPE, particularly those for whom conventional biopsy is contraindicated or declined.