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Günter Klöppel

Gastroenteropancreatic neuroendocrine neoplasms (GEP-NENs) are composed of cells with a neuroendocrine phenotype. The old and the new WHO classifications distinguish between well-differentiated and poorly differentiated neoplasms. All well-differentiated neoplasms, regardless of whether they behave benignly or develop metastases, will be called neuroendocrine tumours (NETs), and graded G1 (Ki67 <2%) or G2 (Ki67 2–20%). All poorly differentiated neoplasms will be termed neuroendocrine carcinomas (NECs) and graded G3 (Ki67 >20%). To stratify the GEP-NETs and GEP-NECs regarding their prognosis, they are now further classified according to TNM-stage systems that were recently proposed by the European Neuroendocrine Tumour Society (ENETS) and the AJCC/UICC. In the light of these criteria the pathology and biology of the various NETs and NECs of the gastrointestinal tract (including the oesophagus) and the pancreas are reviewed.

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Atsuko Kasajima and Günter Klöppel

The bronchopulmonary (BP) and gastroenteropancreatic (GEP) organ systems harbor the majority of the neuroendocrine neoplasms (NENs) of the body, comprising 20 and 70% of all NENs, respectively. Common to both NEN groups is a classification distinguishing between well- and poorly differentiated NENs associated with distinct genetic profiles. Differences between the two groups concern the reciprocal prevalence of well and poorly differentiated neoplasms, the application of a Ki67-based grading, the variety of histological patterns, the diversity of hormone expression and associated syndromes, the variable involvement in hereditary tumor syndromes, and the peculiarities of genetic changes. This review focuses on a detailed comparison of BP-NENs with GEP-NENs with the aim of highlighting and discussing the most obvious differences. Despite obvious differences, the principle therapeutical options are still the same for both NEN groups, but with further progress in genetics, more targeted therapy strategies can be expected in future.

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Zhengping Zhuang, Chunzhang Yang, Ales Ryska, Yuan Ji, Yingyong Hou, Sky D Graybill, Petra Bullova, Irina A Lubensky, Günter Klöppel, and Karel Pacak

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Atsuko Kasajima, Yuichi Ishikawa, Ayaka Iwata, Katja Steiger, Naomi Oka, Hirotaka Ishida, Akira Sakurada, Hiroyoshi Suzuki, Toru Kameya, Björn Konukiewitz, Günter Klöppel, Yoshinori Okada, Hironobu Sasano, and Wilko Weichert

In the light of novel cancer immune therapies, the status of antitumor inflammatory response and its regulation has gained much attention in patients with lung cancer. Ample datasets exist for non-small-cell lung cancer, but those for pulmonary neuroendocrine tumors are scarce and controversial. Here, tumor-associated inflammation, CD8+ cell infiltration and PD-L1 status were evaluated in a cohort of 57 resected carcinoids and 185 resected neuroendocrine carcinomas of the lung (58 large cell carcinomas and 127 small cell carcinomas). Data were correlated with clinicopathological factors and survival. Moderate or high tumor-associated inflammation was detected in 4 carcinoids (7%) and in 37 neuroendocrine carcinomas (20%). PD-L1 immunoreactivity was seen in immune cells of 73 (39%) neuroendocrine carcinomas, while tumor cells were labeled in 21 (11%) cases. Inflammatory cells and tumor cells in carcinoids lacked any PD-L1 expression. In neuroendocrine carcinomas, PD-L1 positivity in immune cells, but not in tumor cells, was associated with intratumoral CD8+ cell infiltration (P < 0.001), as well as with the severity of tumor-associated inflammation (P < 0.001). In neuroendocrine carcinomas, tumor-associated inflammation and PD-L1 positivity in immune cells correlated with prolonged survival and the latter factor was also an independent prognosticator (P < 0.01, hazard ratio 0.4 for overall survival, P < 0.001 hazard ratio 0.4 for disease-free survival). Taken together, in neuroendocrine tumors, antitumor inflammatory response and PD-L1 expression are largely restricted to neuroendocrine carcinomas, and in this tumor entity, PD-L1 expression in inflammatory cells is positively correlated to patient survival.

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Nele Garbrecht, Martin Anlauf, Anja Schmitt, Tobias Henopp, Bence Sipos, Andreas Raffel, Claus F Eisenberger, Wolfram T Knoefel, Marianne Pavel, Christian Fottner, Thomas J Musholt, Anja Rinke, Rudolf Arnold, Uta Berndt, Ursula Plöckinger, Bertram Wiedenmann, Holger Moch, Philipp U Heitz, Paul Komminoth, Aurel Perren, and Günter Klöppel

Somatostatin-producing neuroendocrine tumors (SOM-NETs) of the duodenum and pancreas appear to be heterogeneous. To determine their clinicopathological profiles, respective data were analyzed on a series of 82 duodenal and 541 pancreatic NETs. In addition, the clinical records of 821 patients with duodenal or pancreatic NETs were reviewed for evidence of a somatostatinoma syndrome. Predominant or exclusive expression of somatostatin was found in 21 (26%) duodenal and 21 (4%) pancreatic NETs. They were classified as sporadic (n=31) or neurofibromatosis type 1 (NF1)-associated duodenal NETs (n=3), gangliocytic paragangliomas (GCPGs; n=6), or poorly differentiated neuroendocrine carcinomas (pdNECs; n=2). In addition, five duodenal and four pancreatic SOM-NETs were found in five patients with multiple endocrine neoplasia type 1 (MEN1). Metastases occurred in 13 (43%) patients with sporadic or NF1-associated SOM-NETs, but in none of the duodenal or pancreatic MEN1-associated SOM-NETs or GCPGs. Sporadic advanced (stage IV) SOM-NETs were more commonly detected in the pancreas than in the duodenum. None of the patients (including the 821 patients for whom only the clinical records were reviewed) fulfilled the criteria of a somatostatinoma syndrome. Our data show that somatostatin expression is not only seen in sporadic NETs but may also occur in GCPGs, pdNECs, and hereditary NETs. Surgical treatment is effective in most duodenal and many pancreatic SOM-NETs. MEN1-associated SOM-NETs and GCPGs follow a benign course, while somatostatin-producing pdNECs are aggressive neoplasms. The occurrence of the so-called somatostatinoma syndrome appears to be extremely uncommon.