The International System for Reporting Serous Fluid Cytopathology-An Updated Review

The International System (TIS) for reporting serous fluid cytopathology was published in December 2020 as a joint project by the International Academy of Cytology and the American Society of Cytopathology. The purpose was to standardize the diagnostic criteria and nomenclature used in reporting serous fluid samples, thereby improving the reproducibility of reports and improving communication between pathologists and clinicians. TIS defines a five-tier system consisting of nondiagnostic, negative for malignancy, atypia of uncertain significance, suspicious for malignancy and malignant categories. This review provides an updated summary of the reporting system, risk of malignancy, potential diagnostic pitfalls, and a practical diagnostic approach to serous fluid specimens.