Evaluating the risk of malignancies of the diagnostic categories proposed by the World Health Organization System for Reporting Lung Cytopathology: a two-year single institutional experience.

Introduction The WHO System of Reporting Lung Cytopathology proposed a 5-tiered system in 2023. We report the risk of malignancies (ROMs) of bronchial washing/lavage and percutaneous fine needle aspiration (FNA) specimens. We also evaluated the change of ROMs when image correlation is required. Methods Lung cytology cases in 2021 and 2022 with histologic follow-up were included. CT reports were reviewed to identify cases with a solid nodule/tumor but benign cytological findings. These were reassigned from the "Benign" to "Non-diagnostic" category, and the ROMs were re-estimated. Results A total of 1031 bronchial washing/lavage and 206 FNAs were identified. The ROMs of bronchial washing/lavage were "Non-diagnostic" 56.5% (13/23), "Benign" 41.9% (320/764), "Atypical" 71.7% (71/99), "Suspicious for malignancy" 94.7% (72/76), and "Malignant" 100% (70/70). The ROMs of FNAs were "Non-diagnostic" 66% (33/50), "Benign" 58.2% (39/67), "Atypical" 70% (28/40), "Suspicious for malignancy" 96.2% (25/26), and "Malignant" 100% (70/70). When image finding was considered, cases initially assigned as "Benign" were re-classified to "Non-diagnostic" with decreases in ROMs for the "Benign " category. Conclusions Malignancy risks associated with the WHO System of Reporting Lung Cytopathology diagnostic groups were reported. Image correlation for the "Benign" category led to a decrease in case number and ROM.