Diagnostic accuracy and clinical significance of the fine needle aspiration Ki-67 labelling index in pancreatic endocrine tumours.

Although pancreatic neuroendocrine tumours (PETs) are rare, autopsy series have revealed a high incidence ranging from 0.8 to 10%, reflecting their relative lack of progression and low malignant potential (Kaltsas et al. 2004). Following the application of current sensitive imaging modalities, it is highly probable that the identification of such lesions will increase (Bruzoni et al. 2008). Although biochemical and/or imaging modalities may help differentiate them from evolving adenocarcinoma, histological confirmation remains the definitive diagnostic procedure. Fine needle aspiration and biopsy (FNAB) of pancreatic lesions can be easily performed during endoscopic ultrasonography (EUS), allowing for the preoperative cytological characterisation of such lesions and the estimation of biological behaviour through Ki-67 labelling index (LI) estimation (Kaltsas et al. 2004). To date, only one study has compared the EUS-FNAB cytological Ki-67LI estimation in 18 patients with surgically obtained histological Ki-67LI, demonstrating an overall good agreement, particularly with low Ki-67LI values (Piani et al. 2008). This relative paucity of data prompted us to review 26 patients who had cytological and histological Ki-67LI estimation. All EUS-FNABprocedureswere performed by the same operator and evaluated by the same cytologist. All histological samples were reviewed by one pathologist who also reviewed in a blindmanner the cytological specimens to delineate the level of concordance between cytologist and pathologist. Comparison was based on the WHO 2010 grading system (Bosman et al. 2010) using the k-statistic. The cytological assessment of the Ki-67LI revealed that 15 (58%) of tumours could be classified as G1, nine (34%) as G2 and two (8%) as G3. The histological assessment of the surgical samples classified 11 (42%) tumours as G1, 13 (50%) as G2 and two (8%) as G3 (Table 1). An agreement between the cytological and the histological Ki-67LI expression was found in 7/11 (64%) patients