Risk of malignancy associated with diagnostic categories of the proposed World Health Organization International System for Reporting Pancreaticobiliary Cytopathology.

ABSTRACT

BACKGROUND: The World Health Organization (WHO) has proposed an updated international classification system for reporting pancreaticobiliary cytology. Substantial changes to the prior Papanicolaou Society of Cytopathology (PSC) system have been recommended. Chiefly, the "neoplastic benign" and "neoplastic other" categories have been replaced by 2 new categories-"pancreatic neoplasia-low-grade" (PaN-Low) and "pancreatic neoplasia-high-grade" (PaN-High)-stratifying neoplastic mucinous cysts by cytological atypia. Low-grade malignancies are placed in the "malignant" category and benign serous cystadenoma in the "benign/negative" category. Risk of malignancy (ROM) associated with the diagnostic categories of the WHO system has yet to be defined. METHODS: All patients who underwent endoscopic ultrasound-guided fine-needle aspiration (EUS-FNA) for a pancreatic lesion at a single institution from January 2016 to December 2016, prospectively classified using the PSC system, were reclassified using the WHO system. Absolute ROM was determined by histologic outcome and/or clinical follow-up of at least 6 months. RESULTS: A total of 334 EUS-FNA samples from 322 patients were reviewed and reclassified. Absolute ROM for the WHO system was 7.7% for "insufficient/inadequate/nondiagnostic" category, 1.0% for "benign/negative for malignancy," 28.0% for "atypical," 4.8% for "PaN-Low," 60.0% for "PaN-High," 100% for "suspicious for malignancy," and 100% for "malignant;" the absolute ROM for the same cohort using the PSC system was 7.7% for "nondiagnostic" category, 1.0% for "negative (for malignancy)," 28.0% for "atypical," 0.0% for "neoplastic benign," 30.3% for "neoplastic other," 100% for "suspicious (for malignancy)," and 100% for "positive or malignant." CONCLUSIONS: The WHO international system achieves improved stratification by associated ROM compared to the PSC system.