Pancreatic neuroendocrine tumors: new aspects of morphological classification (World Health Organization, 2017)

The fourth edition of the World Health Organization (WHO) classification of endocrine tumors published in 2017 contains substantial new findings in the topics of pancreatic neuroendocrine neoplasms (PanNENs). In this edition, major modifications are mainly based on new molecular knowledge as well as the clinical behaviour of these tumors accommodated since the previous 2010 classification of degestive tumors was published. According to the new classification scheme PanNENs include malignant well-differentiated neuroendocrine neoplasms (NENs), which are called pancreatic neuroendocrine tumors (PanNETs), and poorly differentiated NENs, which are called pancreatic neuroendocrine carcinomas (PanNECs). PanNENs futher divided into three Grade (G) on the base of cell proliferation: G1 (<2 mitoses on 10 HPF (high-power field) and Ki-67 Index <3 %), G2 (2–20 mitoses on 10 HPF or Ki-67 Index 3–20 %), G3 (>20 mitoses on 10 HPF or Ki-67 Index >20 %). The new category NET G3 was first introduced in this edition of the WHO classification. PanNECs is classified as G3 neoplasms (>20 mitoses on 10 HPF or Ki-67 Index >20 %) and additionally divided into small cell NEC and large cell NEC. In this review we focus on some of the new features of PanNETs and recommended changes of their terminology and classification