EVALUATING THE RISK OF MALIGNANCY IN SEROUS EFFUSIONS USING THE INTERNATIONAL SYSTEM FOR REPORTING SEROUS FLUID CYTOPATHOLOGY (TIS)

Background: Serous effusions are a common clinical presentation encountered in cytopathology. The International System (TIS) for Reporting Serous Fluid Cytopathology provides a standardized five-tier diagnostic framework to improve consistency and uniformity in diagnosis and clinical communication. Objective: To categorize serous effusion samples according to TIS and assess the risk of malignancy (ROM) in each category. Methods: This prospective observational study analyzed 438 serous fluid samples (pleural, peritoneal, and pericardial) at a tertiary care center. Cytological smears were categorized into Non-Diagnostic (ND), Negative for Malignancy (NFM), Atypia of Undetermined Significance (AUS), Suspicious for Malignancy (SFM), and Malignant (MAL). ROM was calculated based on follow-up histopathology, immunohistochemistry (IHC), or radiology. Results: Distribution across categories was: ND (1.14%), NFM (90.86%), AUS (1.36%), SFM (2.28%), and MAL (4.33%). The corresponding ROMs were 20%, 11.55%, 66.67%, 80%, and 100%, respectively. ROM varied by fluid type, with the highest predictive value observed in SFM and MAL categories across all sample types. Conclusion: The TIS framework effectively stratifies the risk of malignancy in serous effusions, aiding in diagnostic precision and clinical decision-making. High ROM in AUS and SFM highlights the need for vigilant follow-up and additional investigations in these groups.