Cytodiagnosis of pleural effusions according to the International System for Reporting Serous Fluid Cytopathology: retrospective analysis of oncological dispensary experience

BACKGROUND: The International Serous Fluid Cytopathology Reporting System (TIS RSFC) was proposed in 2020 to standardize cytological reports and include information on perceived risk of malignancy in reports. It is necessary to analyze the use of TIS RSFC to determine the principles of rational practical implementation and possible improvement of this classification.

AIM: To assess the possibility and results of the application of TIS RSFC (2020) in the cytodiagnosis of pleural effusions using the organizational technologies and resources of a regional oncological dispensary.

METHODS: This observational, retrospective, crossover study carried out a comparative analysis of reports following cytological examination of pleural effusion with clinical and anamnestic information, histological, immunohistochemical results of 1507 patients of the Altai Regional Oncological Dispensary (Barnaul) from 2019 to 2021. The microscope slides were prepared by the traditional smear method, as well as by liquid cytology methods. Papanicolaou and Pappenheim staining methods were used. In certain cases, immunocytochemical tests were performed additionally.

RESULTS: The following numbers of cytological reports corresponding to the TIS RSFC categories were formulated: non-diagnostic material, C I — 11 (0.7%); absence of malignant tumor cells, C II — 946 (62.8%); atypia of unknown significance, C III — 61 (4.0%); suspicion of a malignant process, C IV — 13 (0.9%); malignant process, C V — 476 (31.6%). Within category C V there were 37 (7.8%) cases of the primary tumor — mesothelioma; 398 (83.6%) cases of metastatic tumors, including 41 (8.6%) cases of non-epithelial tumors. Immunocytochemical tests of pleural fluid were performed in 273 (18.1%) cases. Risk of malignancy was 9.1% (1/11) for C I; 1.2% (11/946) — for C II; 59.0% (36/61) — for C III; 84.6% (11/13) — for C IV, and 100% — (476/476) for C V. Cytodiagnosis with immunocytochemistry in unclear cases was characterized by a sensitivity of 92.5%, a specificity of 100%, a positive predictive value of 100%, a negative predictive value of 88.5%, and an accuracy of 96.6%.

CONCLUSIONS: The application of TIS RSFC (2020) in cytological tests of pleural fluid does not cause difficulties for specialists in cytological laboratory. If the required diagnostic accuracy of cytological tests is available, this system makes it possible to characterize the risk of malignancy and thus guide the oncologist in the case management. The liquid-based cytology and the addition of traditional cytological techniques with immunocytochemical tests increase the cytodiagnostic sensitivity.