TIS categorization stratifies pericardial effusion malignancy risk from 10.8% to 78.6% across categories.

BACKGROUND: The International System for Reporting Serous Fluid Cytopathology (TIS) provides a standardized framework for classifying serous fluid cytology into five diagnostic categories: nondiagnostic, negative for malignancy, atypical, suspicious for malignancy, and malignant. Although TIS has been widely adopted for pleural and peritoneal fluids, its application in pericardial effusion cytology remains limited. The objective of this study was to evaluate the use of TIS in pericardial effusion samples and estimate the associated risk of malignancy for each category. METHODS: A systematic review was conducted according to PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. Studies published between 2013 and 2023 were identified through a comprehensive PubMed search. Eligible studies applied TIS to pericardial effusion cytology. The analysis excluded case reports, case reviews, abstracts, comparative studies, and non-English publications. Furthermore, the authors omitted studies that did not explicitly categorize pericardial fluid samples using the TIS categorization. Ten studies met inclusion criteria, comprising 2976 pericardial fluid samples. RESULTS: The pooled distribution across TIS categories were: nondiagnostic (2.9%), negative for malignancy (60.2%), atypical (5.4%), suspicious for malignancy (2.4%), and malignant (23.4%). Risk of malignancy estimates based on histologic confirmation were: 10.8% for nondiagnostic, 8.7% for negative for malignancy, 34.0% for atypical, 64.1% for suspicious for malignancy, and 78.6% for malignant categories. CONCLUSIONS: TIS effectively stratifies pericardial effusion cytology samples by malignancy risk. The progressive increase in the risk of malignancy across categories supports its diagnostic utility. However, substantial heterogeneity, particularly in the negative for malignancy and malignant categories, highlights the need for standardized reporting and further prospective validation of TIS.