Pleural Fluid Cytology-Histology Correlation in Patients With Malignant Pleural Mesothelioma: A Series of 26 Cases

Cytopathology 2026 February 20 [Link]

John Findley, Matthew Demetrious, Lucas Yan, Lei Yan

Abstract

Background: To understand the efficacy of pleural effusion cytology in the diagnosis of malignant mesothelioma, we conducted this retrospective study to review the pleural fluid cytologies of patients diagnosed on concurrent/recent pleural biopsy histology. The clinicopathologic features and common cytomorphology were analysed.

Methods: Patients who underwent pleural biopsy/stripping and had concurrent/recent pleural fluid cytology between May 2004 and December 2023 at Rush University Medical Center in Chicago were included in our study. All pleural fluid specimens initially collected and preserved in CytoLyt Solution (Hologic, Marlborough, MA) were processed into ThinPrep slides using a standardised laboratory protocol. The cytology diagnoses were made based on a combination of Papanicolaou stained ThinPrep slides, H&E stained cell block and immunohistochemistry on cell block.

Results: A total of 26 patients with malignant pleural mesothelioma diagnosed on pleural biopsy/stripping who also had concurrent/recent pleural fluid cytology were identified. About 53.8% (14/26) of pleural fluid cytologies were negative. The most common initial interpretations for the negative findings were reactive mesothelial cells (8/14), mixed inflammatory cells (12/14) and macrophages (2/14). Indeterminate pleural fluid cytologies accounted for 19.2% (5/26) of specimens in our study, with 11.5% being atypical and 7.7% suspicious for malignancy. Malignant pleural fluid cytologies accounted for 26.9% (7/26) of our cases. Surgical pathology specimens included 22 pleural biopsies and 4 pleural strippings, all of which confirmed malignant pleural mesothelioma. The subtypes of malignant pleural mesothelioma included 18 epithelioid, 4 sarcomatoid and 4 biphasic mesothelioma subtypes. The sensitivity of pleural fluid cytology alone in our study was low, at 26.9%. However, when including the ‘Atypical cells present’ and ‘Suspicious for malignancy’ categories as abnormal cytology, the sensitivity increased to 46.2%.

Conclusion: In conclusion, we report that a diagnosis of mesothelioma can be made from pleural fluid cytology samples in a subset of patients, albeit with a relatively low sensitivity (26.9%).