The New WHO Lung Cytopathology Reporting System in Practice: Diagnostic Performance and Risk of Malignancy in a Tertiary Care Setting

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BACKGROUND: Respiratory cytology plays a vital role in the early diagnosis of pulmonary diseases, particularly lung cancer, which remains a leading cause of cancer-related mortality worldwide. To enhance standardization and reduce inter-observer variability in lung cytology reporting, the World Health Organization (WHO), in collaboration with the IAC and IARC, introduced a new five-tiered reporting system for lung cytopathology in 2023. This study aims to retrospectively apply the WHO system to respiratory samples at a tertiary care center in India and evaluate diagnostic performance and risk of malignancy (ROM) for each category. MATERIAL AND METHODS: A retrospective observational study was conducted from June 2022 to May 2024, analyzing 736 respiratory cytology samples, including BAL, EBUS-TBNA, bronchial wash, bronchial brush, and sputum. Samples were reclassified using the WHO system, and 193 cases had histopathological correlation. ROM was calculated for each category, and diagnostic performance metrics sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and diagnostic accuracy (DA) were assessed using histopathology as the gold standard. Given that histologic correlation was available in only 26.2% of cases, diagnostic performance estimates were interpreted with caution and may have been influenced by verification bias. RESULTS: Of the total cases, 10.2% (75/736) were insufficient/inadequate, 80.1% (589/736) benign, 3.0% (22/736) atypical, 2.0% (15/736) suspicious, and 4.7% (35/736) malignant. The ROM was 43.7% for insufficient, 39.7% for benign, 50.0% for atypical, 75.0% for suspicious, and 100% for malignant. Bronchial brush demonstrated the highest DA (81.3%), while BAL had low sensitivity (10.0%) despite high specificity (98.5%). EBUS-TBNA showed moderate sensitivity (50.0%) and lower specificity (55.6%). CONCLUSION: The WHO Reporting System provides an effective framework for stratifying respiratory cytology samples. While categories such as malignant and suspicious showed high diagnostic reliability, false negatives in benign and inadequate categories highlight the need for integrated clinical and radiological assessment. Bronchial brush and wash emerged as the most diagnostically accurate specimen types. Further prospective studies are warranted to validate these findings across broader clinical settings.

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