Evaluating the Risk of Malignancies of the Diagnostic Categories Proposed by the World Health Organization System for Reporting Lung Cytopathology: A 2-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 1,031 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.