Cytology-Histology Correlation of Lung EBUS FNA with the WHO Reporting System for Lung Cytopathology: An Institutional Experience

Summary: Introduction: The International Academy of Cytology and the International Agency for Research on Cancer developed the World Health Organization (WHO) Reporting System for Lung Cytopathology in 2022. Our aim is to evaluate this classification system by examining endobronchial ultrasound (EBUS) fine needle aspiration (FNA) specimens of intrathoracic lesions and their corresponding histologic diagnosis. Materials and Methods: This study was performed as part of the cytology-histology correlation mandated under CLIA88. Our institution requires residents to perform a site-specific review of cytologic specimens for laboratory quality assurance. A system-wide retrospective review of lung EBUS FNAs was performed within our institution from 2022 to 2023. Data was retrieved from our laboratory information system. 1162 lung EBUSs were performed on 1022 patients. The risk of malignancy (ROM) was determined using a malignant biopsy or resection diagnosis as a positive test result. Results: Our institution was an early adopter of the 2022 WHO lung cytology reporting system. The correct WHO category was utilized for 1147 (98.7%) cases. There were 15 (1.3%) cases that did not utilize the WHO categories and were categorized as ""Neoplasm"", which included solitary fibrous tumor and low-grade neuroendocrine tumor. The final cytology correlated with histology in 901 (90.5%) cases. Cytology-histology correlation was greatest in cases classified as ""Benign"" (93.5%), ""Suspicious for malignancy"" (94%) or ""Malignant"" (94%). The ROM for each WHO category is summarized in Table 1. Conclusions: Our institution's ROM calculations are congruent with the WHO reporting system. For cases called ""Neoplasm"", these could be reclassified as ""Benign"" or ""Malignant"" in retrospect. In the context of EBUS-guided FNA, the WHO system performs well, with few non-concordant follow-up surgical pathology results. Discrepancies in cytopathology and histopathology correlations may be due to various factors such as inaccurate initial classification on cytology and sampling issues.