Pancreatic neuroendocrine tumours: a comparison of cytological classification systems

Cytological classification systems provide a standardised interpretation framework for reporting cytological specimens. Three well-known classification systems can be applied when reporting pancreatic cytology. This study aimed to compare the accuracy of these classification systems (C1-C5 system, the Papanicolaou system and the WHO classification) for the assessment of pancreatic neuroendocrine lesions.

We analysed 73 pancreatic neuroendocrine tumour resections, 49 of which had corroborative cytology available, reported over a 12-year period, at a single UK tertiary referral centre. Each cytology case was classified using the aforementioned systems. The final tumour grade allocated at resection was used to assess and compare the accuracy of each cytological classification system.

Cytological assessment accurately reported 77.6% of neuroendocrine lesions as category IVB (neoplastic - other) on Papanicolaou grading, 77.6% as C5 (malignant) lesions and 85.7% as VII (malignant) on WHO grading. 74.3% of resected tumours were grade 1, 17.1% grade 2 and 8.6% grade 3. Complete resection was achieved in 80.8% of cases.

The results demonstrated that the WHO classification appeared to provide reduced ambiguity when compared with both 'C' and Papanicolaou classification systems; with a lower proportion of cases being classified as suspicious of malignancy as opposed to malignant. The Papanicolaou system was able to supersede the other two systems through its ability to distinguish neuroendocrine tumours from more aggressive entities such as pancreatic adenocarcinoma, thus, offering flexibility in management while still retaining a similar level of accuracy to the WHO classification system in distinguishing benign from malignant lesions.