WHO 2010 classification of pancreatic endocrine tumors. is the new always better than the old?

BACKGROUND: In 2010, the World Health Organization released a new classification system for endocrine pancreatic tumors. The new categories replaced those in the old classification. METHODS: To test the safety and accuracy of the new classification in stratifying patients, we retrospectively evaluated 64 consecutive patients, surgically R0 resected for pancreatic endocrine tumors. RESULTS: In our experience, only 19/31 (61.3%) patients classified as having well-differentiated tumors were included in the new neuroendocrine tumor G1 category while the remaining 12 (38.7%) shifted into the G2 category. Moreover, 10/33 (30.3%) patients classified as affected by a malignant endocrine neoplasm in the old system were considered as G1 tumors in the new one. These differences were statistically significant (P < 0.001) and changed the risk category in 22 (33.3%) patients with well-differentiated pancreatic endocrine tumors. Multiple multivariate models were produced and the poor stratification of the new system was found to be in the G2 category which presents too wide a range of the Ki 67 index (2 to 20%). We built a model in which the G2 category was divided into two subcategories: tumors with a Ki 67 index ≥2 and