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

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.

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.

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 <15 mm and depended on the anatomical site with the highest ROL in abdominal/pelvic and the highest ROMet in axillary/mammary lymph nodes. The ROL-to-ROMet ratio was higher if the question was lymphoma (36.7%-8.0%) or unspecified (8.3%-8.3%) compared to any other question.

The WHO system demonstrates high diagnostic accuracy, increasing with the use of ancillary techniques, particularly flow cytometry. The ROM, ROL, and ROMet depend on lymph node size, the anatomical site, and the clinical question. A lymph node size of 10 mm may be an appropriate threshold for further investigation, depending on the clinical context.