Diagnostic performance and clinical implications of the World Health Organization Reporting System for Lymph Node Cytopathology

INTRODUCTION: A World Health Organization (WHO) system has recently been introduced to standardize reporting of lymph node fine-needle aspiration biopsy (LN-FNAB) cytopathology. Herein, we analyze its diagnostic performance in a routine setting. MATERIALS AND METHODS: We reviewed 2274 consecutive lymph node fine-needle aspiration biopsies categorized according to the WHO system. Corresponding histological material, radiological images, or uneventful clinical follow-up over 12 months were used as ground truths for classifying LNs as malignant or benign. RESULTS: The diagnostic accuracy of the WHO system was 91.8% without and 95.9% with ancillary techniques. The risk of malignancy (ROM) was 21.8% for the "Insufficient/Inadequate/Non-diagnostic", 6.6% for the "Benign", 29.7% for the "Atypical", 91.2% for the "Suspicious for malignancy", and 99.6% for the "Malignant" category. ROM increased with lymph node size, with a significant rise to 33.1% in the 10-14 mm size interval. The ratio of risk of lymphoma (ROL) to risk of metastasis (ROMet) was significantly lower in lymph nodes