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

In 2010, the World Health Organization released a new classification system for endocrine pancreatic tumors. The new categories replaced those in the old classification.

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.

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 <5% and tumors with a Ki index ≥5 and <20%, partially modifying the new classification. In this model, the modified classification showed a superiority with respect to the European Neuroendocrine tumor Society-Tumor-Node-Metastasis staging system in stratifying patients for recurrence, with a relative risk of 19 (P < 0.001).

The new G2 category seems too large because it includes both benign, low and high grade malignant tumors.