Historical, current and future perspectives on gastrointestinal and pancreatic endocrine tumors

[Neuroendocrine neoplasms : Two families with distinct features unified in one classification (German version)]

All neuroendocrine neoplasms (NENs) are characterized by the expression of synaptophysin and chromogranin A (or B). Yet, they are not a homogeneous group of tumors. Paradigmatic for these tumors are the NENs of the gastroenteropancreatic (GEP) system. Two NEN families can be distinguished: predominantly well differentiated and low-proliferative NENs, called neuroendocrine tumors (NET), and poorly differentiated and high-proliferative NENs, called neuroendocrine carcinomas (NECs). Based on their proliferative activity, GEP NETs are further classified into G1, G2, and G3 tumors. NECs are per definition G3 carcinomas. The morphological NEN dichotomy is supported by differences in epidemiology, genetics, clinics, and prognosis, and potentially has its cause originating from different progenitor cells. Genetically, NECs are distinguished by TP53 and RB1 alterations, which are lacking in NETs and are helpful in the distinction of NETs from NECs. Comparison of the GEP NEN WHO classification with extragastroenteropancreatic NEN classifications commonly reveal differences in terminology and categorization. In addition, they lack a grading system. However, common to all NEN classifications is the recognition of two tumor families differing in histological differentiation and prognosis. This allows the construction of a uniform classification frame for all NENs.

Neuroendocrine Neoplasms: Dichotomy, Origin and Classifications

Neuroendocrine neoplasms (NENs) are heterogeneous tumors with a common phenotype. There are two fundamentally different groups of NENs: well-differentiated, low-proliferating NENs, called neuroendocrine tumors (NETs) or carcinoids, and poorly differentiated, highly proliferating NENs, called small- or large-cell neuroendocrine carcinomas (NECs). This NEN dichotomy is probably due to an origin from different neuroendocrine progenitor cells. The current World Health Organization (WHO) classification of gastrointestinal NENs uses the Ki67 proliferation index to grade NETs as G1 or G2, and NECs as G3. In the pancreas, NETs and NECs may overlap in their proliferation index, making the distinction between them difficult and leading to therapeutic uncertainties. Therefore, the WHO classification of pancreatic NENs (PanNENs) from 2017 introduced a new NET G3 category. Helpful for the distinction of NETs G3 from NECs is the expression of p53 and rb1 that is usually negative in PanNETs. Comparison of the WHO classification of digestive system NENs with other NEN classifications reveals site-specific differences in terminology and a general lack of grading systems. However, all classifications recognize the existence of the two major NEN families and provide a general basis for their prognostic and therapeutic stratification. A development of a common NEN classification across organs is desirable.

Fluorine-18 labeled amino acids for tumor PET/CT imaging

Tumor glucose metabolism and amino acid metabolism are usually enhanced, ¹⁸F-FDG for tumor glucose metabolism PET imaging has been clinically well known, but tumor amino acid metabolism PET imaging is not clinically familiar. Radiolabeled amino acids (AAs) are an important class of PET/CT tracers that target the upregulated amino acid transporters to show elevated amino acid metabolism in tumor cells. Radiolabeled amino acids were observed to have high uptake in tumor cells but low in normal tissues and inflammatory tissues. The radionuclides used in labeling amino acids include ¹⁵O, ¹³N, ¹¹C, ¹²³I, ¹⁸F and ⁶⁸Ga, among which the most commonly used is ¹⁸F [1]. Available data support the use of certain ¹⁸F-labeled AAs for PET/CT imaging of gliomas, neuroendocrine tumors, prostate cancer and breast cancer [2, 3]. With the progress of the method of ¹⁸F labeling AAs [4-6], ¹⁸F-labeled AAs are well established for tumor PET/CT imaging. This review focuses on the current status of key clinical applications of 18F-labeled AAs in tumor PET/CT imaging.

Pancreatic Neuroendocrine Neoplasms

Pancreatic neuroendocrine neoplasms (Pan-NENs) are rare but clinically important lesions. Pan-NENs are known for and often categorized by their capacity to produce clinical syndromes mediated by the production of hormones. Despite sometimes presenting dramatically from excessive hormone production, not all Pan-NENs produce functional hormone, and they can pose diagnostic challenges to practicing pathologists. Distinguishing Pan-NENs from mimics can be crucial, because Pan-NENs carry different prognoses and have unique treatments available due to their specific biological properties. This article reviews the current categorization and features of Pan-NENs.

Different gene expression profiles in metastasizing midgut carcinoid tumors

The genetic events leading the progression of midgut carcinoid tumors are largely unknown. The disease course varies from patient to patient, and there is a lack of reliable prognostic markers. In order to identify genes involved in tumor progression, gene expression profiling was performed on tumor specimens. Samples comprised 18 primary tumors, 17 lymph node (LN) metastases, and seven liver metastases from a total of 19 patients. Patients were grouped according to clinical data and histopathology into indolent or progressive course. RNA was subjected to a spotted oligo microarray and B-statistics were performed. Differentially expressed genes were verified using quantitative real-time PCR. Self-organizing maps demonstrated three clusters: 11 primary tumors separated in one cluster, five LN metastases in another cluster, whereas all seven liver metastases, seven primary, and 12 LN metastases formed a third cluster. There was no correlation between indolent and progressive behavior. The primary tumors with Ki67 >5%, with low frequency of the carcinoid syndrome, and a tendency toward shorter survival grouped together. Primary tumors differed in expression profile from their associated LN metastases; thus, there is evidence for genetic changes from primary tumors to metastases. ACTG2, GREM2, REG3A, TUSC2, RUNX1, TPH1, TGFBR2, and CDH6 were differentially expressed between clusters and subgroups of tumors. The expression profile that assembles tumors as being genetically similar on the RNA expression level may not be concordant with the clinical disease course. This study reveals differences in gene expression profiles and novel genes that may be of importance in midgut carcinoid tumor progression.

The origin of neuroendocrine tumors and the neural crest saga

In this essay, the role of the neural crest in the development of the vertebrate embryo is briefly described. The techniques used to document the neural crest origin of various cell types and the tumors arising from them are discussed, with emphasis on Le Douarin's quail-chick chimera model. The current dogma on the origin of the cells of the diffuse endocrine system is presented, and some personal conjectures based on the microscopic appearances of various types of normal, vestigial and neoplastic human tissues are offered to the reader as 'food for thought.'

Mucin-producing gallbladder adenocarcinoma with focal small cell and large cell neuroendocrine differentiation associated with pancreaticobiliary maljunction

Herein is reported a case of mucin-producing carcinoma of the gallbladder in a 55-year-old Japanese woman. Although the patient's status and laboratory data initially suggested biliary pancreatitis due to gallstone, radiography and endoscopy confirmed the presence of pancreaticobiliary maljunction and a gallbladder tumor with excessive mucin, in which the duodenal papilla and the common bile duct were impacted. Following surgery, the gallbladder tumor was histopathologically diagnosed as a mixed endocrine-exocrine carcinoma. The carcinoma predominantly consisted of papillary, but also contained some tubular adenocarcinomatous components. Additionally, small foci of small cell and large cell neuroendocrine carcinomatous components were observed. There was no evidence of lymph node metastasis, distant metastasis, or direct invasion outside the gallbladder. Thus, the final classification of pT2N0M0 stage II was given to this lesion, according to the Union Internationale Contre le Cancer guidelines. The postoperative course was uneventful, and the carcinoma had not recurred in the absence of chemoradiotherapy for a period of 20 months. Mucin-producing gallbladder carcinoma is a rare clinical condition that can occur in patients with pancreaticobiliary maljunction. Detailed investigation of this condition is important to develop and refine effective therapeutic strategies.

Endocrine tumours of the gastrointestinal tract-selected topics

This review provides an update on the pathogenesis and histopathological diagnosis of endocrine tumours of the gastrointestinal tract, concentrating on three different varieties whose careful assessment by pathologists is of particular clinical significance. These are the four types of enterochromaffin-like cell tumour of the gastric corpus, the periampullary somatostatin-containing D-cell tumour of the duodenum, and the frequently chromogranin A-negative L-cell tumour of the appendix and large intestine. In addition, the value of pathological factors in predicting the behaviour of gastrointestinal endocrine tumours and selecting therapy is discussed, and the crucial role of the pathologist in the multidisciplinary team management of these neoplasms is emphasized.

Genes involved in neuroendocrine tumor biology

The fascinating, but often unpredictable, biology of neuroendocrine tumors (NETs) make the management of these malignancies a real challenge. The more recent development of high-throughput genomic and proteomic techniques, have opened a window to an increased knowledge of the biology of NETs. This review will discuss genes thought to play a role in the context of NE tumor biology, with particularly attention to those that may be potential new diagnostic and prognostic markers, as well as therapeutic targets. NETs constitute a heterogeneous group of neoplasm that may arise in virtually every topographic localization in the body, as a consequence of malignant transformation of various types of NE cells. Since NETs arising in the gastroenteropancreatic (GEP) or bronchopulmonary system are by far the most common, this review focuses on these entities, but lines are drawn to other NETs as well. Although large-scale gene expression analysis undoubtly have raised interesting new hypothesis concerning genes thought to play a role in tumor biology, discrepancies observed between studies and various platforms used, emphasizes the need to not only standardize the way microarray data are reported, but also to introduce standards in sample taking, processing and study design. In addition, the recognition of the complexity of the human proteome, with regard to generation of multiple isoforms from one gene, has created additional challenges. However,some goals have been reached already, as new knowledge has been translated into development of novel promising therapeutics.