The World Health Organization classification of pancreaticobiliary cytopathology stratifies risk of malignancy and outcome for endoscopic ultrasound-guided fine-needle aspiration of the pancreas.

Background: The World Health Organization (WHO) has recently published a classification for reporting pancreaticobiliary cytopathology with differences compared to the Papanicolaou Society of Cytopathology (PSC) classification.

Methods: Retrospective data were collected from pancreatic endoscopic ultrasound-guided fine-needle aspirations from 2014 to 2017 at a pancreatic cancer center. Absolute risk of malignancy (AROM), relative risk (to benign), performance characteristics, and overall survival were calculated for the entire cohort with comparison of cysts and solid lesions.

Results: In total, 2562 cases were included: 16% cyst (n = 411) and 84% solid (n = 2151). The histologic confirmation rate was 43% (n = 1101) and the median follow-up (for benign) was 56 months. For WHO I-VII, overall AROM (%) was 23, 22, 62, 13, 65, 97, and 100; cyst AROM was 7, 0, 19, 13, 38, 78, and 100; and solid AROM was 50, 29, 70, 15, 100, 99, and 100. For PSC I-VI, overall AROM (%) was 23, 29, 64, 0 (IVa), 60 (IVb), 97, and 100; cyst AROM was 7, 0, 19, 0, 21, 78, and 100; and solid AROM was 50, 35, 73, 0, 92, 99, and 100. The difference in relative risk for a cyst (vs. solid) overall was 0.38 for WHO and 0.26 for PSC. WHO and PSC categories showed stratification for the probability of overall survival.

Conclusions: Cystic versus solid lesion type can dramatically affect AROM, particularly for nondiagnostic (I), benign (II), atypical (III), and WHO V categories. WHO IV conveys a similarly low AROM for cystic and solid types. Both classifications stratify the probability of overall survival, including the newly introduced categories WHO IV and WHO V.