Pancreatic neuroendocrine tumour grading on endoscopic ultrasound‐guided fine needle aspiration: high reproducibility and inter‐observer agreement of the K i‐67 labelling index

Objectives Assessment of proliferation by the Ki‐67 labelling index ( K i67‐ LI ) is an important parameter of pancreatic neuroendocrine tumour ( pNET ) prognosis on resection specimens. K i67‐ LI values for grading are not fully established on endoscopic ultrasound‐guided fine needle aspiration ( EUS ‐ FNA ). The aim of the study was to determine the accuracy of K i67‐ LI on EUS ‐ FNA to predict a final grade of p NET and to analyse the relationship between cytological grading and progression‐free survival ( PFS ). Methods Between 1996 and 2010, 46 pNETs (33 were resected) from 45 patients were diagnosed by EUS ‐ FNA . Ki67‐LI was evaluated on cytological and histological material for each tumour and classified according to the 2010 WHO grading system. Results A very good inter‐observer agreement for K i67‐ LI on EUS ‐ FNA and surgical specimens, respectively, were obtained. Discrepancies were observed between histology and cytology, especially in grade 2 ( G 2) tumours, where cytology underestimated grading owing to tumour heterogeneity. Still, EUS ‐ FNA was able to distinguish a poor prognostic group, as the actuarial PFS of cytological (c) G3 tumours was 10 ± 4 months versus 29 ± 7 and 68 ± 10 for c G 2 and c G 1 tumours, respectively ( P  < 0.0001). Conclusion This study attests the reproducibility of K i67‐ LI of pNET s whether counted on cytology or histology with a very good inter‐observer correlation. Determination of K i67‐ LI on EUS ‐ FNA of pNETs should be included systematically in their prognostic work‐up.