Definitive Diagnosis of Pleural Mesothelioma by Pleural Effusion Cytology: The MesoCyto Study

Abstract: Objective: We evaluated the possibility of diagnosing pleural mesothelioma (PM) through pleural effusion cytology in a multicentric prospective clinical trial (MesoCyto study). Methods: We included patients with pleural effusion and suspected PM scheduled for thoracentesis and pleural biopsy. Both pleural effusion cytology including cell block and pleural biopsy were independently performed and compared to assess the diagnostic reliability of pleural effusion cytology. The primary endpoint aimed to demonstrate that the specificity of PM diagnosis by pleural effusion cytology reached 100%. Secondary endpoints included the frequency of adverse events during thoracentesis and pleural biopsy and assessment of diagnostic accuracy of pleural effusion cytology for each histological type. Results: Of the 50 enrolled patients, histological examination confirmed PM in 42 patients; 29 patients met the diagnostic criteria of PM in pleural effusion cytology and received a cytological diagnosis. Of the remaining 21 patients, 13 displayed atypical cells suggestive of PM based on pleural effusion cytology but did not meet the diagnostic criteria, and in 8, atypical cells were not identified and PM diagnostic criteria were not met. Thus, pleural effusion cytology specificity was 100%. The diagnostic concordance rate by pleural effusion cytology for each histological type was 72.2% for epithelioid, 75% for biphasic, and 0% for sarcomatoid. No adverse events were associated with thoracentesis, but the incidence of adverse events during pleural biopsy was 14%. Conclusions: PM can potentially be diagnosed through only pleural effusion cytology including the cell block method using immunohistochemical staining.