Chromosomal alterations detected by comparative genomic hybridization in nonfunctioning endocrine pancreatic tumors

All Together Now: Standardization of Nomenclature for Neuroendocrine Neoplasms across Multiple Organs

Neuroendocrine neoplasms (NENs) span virtually all organ systems and exhibit a broad spectrum of behavior, from indolent to highly aggressive. Historically, nomenclature and grading practices have varied widely across, and even within, organ systems. However, certain core features are recapitulated across anatomic sites, including characteristic morphology and the crucial role of proliferative activity in prognostication. A recent emphasis on unifying themes has driven an increasingly standardized approach to NEN classification, as delineated in the World Health Organization's Classification of Tumours series. Here, we review recent developments in NEN classification, with a focus on NENs of the pancreas and lungs.

Centromeric cohesion failure invokes a conserved choreography of chromosomal mis-segregations in pancreatic neuroendocrine tumor

BACKGROUND

Pancreatic neuroendocrine tumors (PANETs) are rare, slow growing cancers that often present with local and distant metastasis upon detection. PANETS contain distinct karyotypes, epigenetic dysregulation, and recurrent mutations in MEN1, ATRX, and DAXX (MAD+); however, the molecular basis of disease progression remains uncharacterized.

METHODS

We evaluated associations between aneuploidy and the MAD+ mutational state of 532 PANETs from 11 published genomic studies and 19 new cases using a combination of exome, targeted panel, shallow WGS, or RNA-seq. We mapped the molecular timing of MAD+ PANET progression using cellular fractions corrected for inferred tumor content.

RESULTS

In 287 PANETs with mutational data, MAD+ tumors always exhibited a highly recurrent signature of loss of heterozygosity (LOH) and copy-number alterations affecting 11 chromosomes, typically followed by genome doubling upon metastasis. These LOH chromosomes substantially overlap with those that undergo non-random mis-segregation due to ectopic CENP-A localization to flanking centromeric regions in DAXX-depleted cell lines. Using expression data from 122 PANETs, we found decreased gene expression in the regions immediately adjacent to the centromere in MAD+ PANETs. Using 43 PANETs from AACR GENIE, we inferred this signature to be preceded by mutations in MEN1, ATRX, and DAXX. We conducted a meta-analysis on 226 PANETs from 8 CGH studies to show an association of this signature with metastatic incidence. Our study shows that MAD+ tumors are a genetically diverse and aggressive subtype of PANETs that display extensive chromosomal loss after MAD+ mutation, which is followed by genome doubling.

CONCLUSIONS

We propose an evolutionary model for a subset of aggressive PANETs that is initiated by mutation of MEN1, ATRX, and DAXX, resulting in defects in centromere cohesion from ectopic CENP-A deposition that leads to selective loss of chromosomes and the LOH phenotype seen in late-stage metastatic PANETs. These insights aid in disease risk stratification and nominate potential therapeutic vulnerabilities to treat this disease.

Ancillary Techniques in Cytologic Specimens Obtained from Solid Lesions of the Pancreas: A Review

Advanced methods of molecular characterization have elucidated the genetic, epigenetic, and proteomic alterations associated with the broad spectrum of pancreatic disease, particularly neoplasia. Next-generation sequencing, in particular, has revealed the genomic diversity among pancreatic ductal adenocarcinoma, neuroendocrine and acinar tumors, solid pseudopapillary neoplasm, and other pancreatico-biliary neoplasms. Differentiating these entities from one another by morphologic analysis alone may be challenging, especially when examining the small quantities of diagnostic material inherent to cytologic specimens. In order to enhance the sensitivity and specificity of pancreatic cytomorphology, multiple diagnostic, prognostic, and predictive ancillary tests have been and continue to be developed. Although a great number of such tests have been developed for evaluation of specimens collected from cystic lesions and strictures, ancillary techniques also play a significant role in the evaluation of cytologic specimens obtained from solid lesions of the pancreas. Furthermore, while some tests have been developed to differentiate diagnostic entities from one another, others have been developed to simply identify dysplasia and malignancy. Ancillary studies are particularly important in the subset of cases for which cytomorphologic analysis provides a result that is equivocal or insufficient to guide clinical management. Selection of appropriate ancillary testing modalities requires familiarity with both their methodology and the molecular basis of the pancreatic diseases for which testing is being performed.

Surgical and molecular pathology of pancreatic neoplasms

BACKGROUND

Histologic characteristics have proven to be very useful for classifying different types of tumors of the pancreas. As a result, the major tumor types in the pancreas have long been classified based on their microscopic appearance.

MAIN BODY

Recent advances in whole exome sequencing, gene expression profiling, and knowledge of tumorigenic pathways have deepened our understanding of the underlying biology of pancreatic neoplasia. These advances have not only confirmed the traditional histologic classification system, but also opened new doors to early diagnosis and targeted treatment.

CONCLUSION

This review discusses the histopathology, genetic and epigenetic alterations and potential treatment targets of the five major malignant pancreatic tumors - pancreatic ductal adenocarcinoma, pancreatic neuroendocrine tumor, solid-pseudopapillary neoplasm, acinar cell carcinoma and pancreatoblastoma.

Pancreatic neuroendocrine tumors: Challenges in an underestimated disease

Pancreatic neuroendocrine tumours (PanNETs) are considered a relatively unusual oncologic entity. Due to its relative good prognosis, surgery remains the goal standard therapy not only in localized disease but also in the setting of locally or metastatic disease. Most of the patients are diagnosed in metastatic scenario, where multidisciplinary approach based on surgery, chemotherapies, liver-directed and/or molecular targeted therapies are commonly used. Owing to a deeper molecular knowledge of this disease, these targeted therapies are nowadays widely implemented, being the likely discovery of predictive biomarkers that would allow its use in other settings. This review is focused on describing the different classifications, etiology, prognostic biomarkers and multidisciplinary approaches that are typically used in PanNET.

Genetics of pancreatic neuroendocrine tumors: implications for the clinic

Pancreatic neuroendocrine tumors (PanNETs) are a common and deadly neoplasm of the pancreas. Although the importance of genetic alterations in PanNETs has been known for many years, recent comprehensive sequencing studies have greatly expanded our knowledge of neuroendocrine tumorigenesis in the pancreas. These studies have identified specific cellular processes that are altered in PanNETs, highlighted alterations with prognostic implications, and pointed to pathways for targeted therapies. In this review, we will discuss the genetic alterations that play a key role in PanNET tumorigenesis, with a specific focus on those alterations with the potential to change the way patients with these neoplasms are diagnosed and treated.

Loss of 11p11 is a frequent and early event in sporadic nonfunctioning pancreatic neuroendocrine neoplasms

The pathogenesis of sporadic pancreatic neuroendocrine neoplasms (PNENs) is poorly understood. To gain insight into the genetic mechanisms underlying this tumor entity, we performed genome-wide screening of 16 surgical specimens from 15 patients with sporadic PNEN, combining G-band karyotyping and high resolution comparative genomic hybridization (HR-CGH). G-banding revealed abnormal karyotypes in 2 of 10 tumor samples analyzed. DNA copy number changes were detected in 13 samples, whereas three tumors showed a balanced genome. Gains were more frequent than losses in the nonfunctioning tumors (n=13). Common gains were scored at 5p12–13, 4q13–24, 5p15, 5q11–31, and 9q21–22. Common losses were scored at 11p11, 11p14–15, 11q23, 11p12–13, and 11q22. The average number of copy aberrations (ANCA index) was 12 for 13 nonfunctioning primary tumors, 4.8 for the nonfunctioning tumors with low Ki-67 (≥5%), 21.2 for the tumors with high Ki-67 (<5%), 2.5 for small tumors (<3.5 cm), and 17.8 for large tumors (≥3.5 cm). There was a statistically significant difference in the ANCA index between the groups defined by Ki-67 and tumor size. Nonfunctioning tumors with low Ki-67, no distant metastasis and small size had few aberrations detected by HR-CGH, but frequent loss of material from chromosomal band 11p11. The present study indicates the existence of distinct cytogenetic patterns in sporadic nonfunctioning PNEN. Loss of chromosomal band 11p11 might indicate a primary pathogenetic event in these tumors.

Gastroenteropancreatic endocrine tumors

Gastroenteropancreatic endocrine tumors (GEP-NETs) are relatively uncommon; comprising approximately 0.5% of all human cancers. Although they often exhibit relatively indolent clinical courses, GEP-NETs have the potential for lethal progression. Due to their scarcity and various technical challenges, GEP-NETs have been understudied. As a consequence, we have few diagnostic, prognostic and predictive biomarkers for these tumors. Early detection and surgical removal is currently the only reliable curative treatment for GEP-NET patients; many of whom, unfortunately, present with advanced disease. Here, we review the genetics and epigenetics of GEP-NETs. The last few years have witnessed unprecedented technological advances in these fields, and their application to GEP-NETS has already led to important new information on the molecular abnormalities underlying them. As outlined here, we expect that "omics" studies will provide us with new diagnostic and prognostic biomarkers, inform the development of improved pre-clinical models, and identify novel therapeutic targets for GEP-NET patients.

Pathology and molecular genetics of pancreatic neoplasms

Cancer is fundamentally a genetic disease caused by the accumulation of somatic mutations in oncogenes and tumor suppressor genes. In the last decade, rapid advances in sequencing and bioinformatic technology led to an explosion in sequencing studies of cancer genomes, greatly expanding our knowledge of the genetic changes underlying a variety of tumor types. Several of these studies of cancer genomes have focused on pancreatic neoplasms, and cancers from the pancreas are some of the best characterized tumors at the genetic level. Pancreatic neoplasms encompass a wide array of clinical diseases, from benign cysts to deadly cancers, and the genetic alterations underlying neoplasms of the pancreas are similarly diverse. This new knowledge of pancreatic cancer genomes has deepened our understanding of tumorigenesis in the pancreas and has opened several promising new avenues for novel diagnostics and therapeutics.

Profiling mTOR pathway in neuroendocrine tumors

The serine/threonine kinase mammalian target of rapamycin (mTOR) plays a central role in regulating critical cellular processes such as growth, proliferation, and protein synthesis. The study of cancer predisposing syndromes within which neuroendocrine tumors (NETs) may arise has furnished clues on the involvement of mTOR pathway in sporadic diseases so far. Recent comprehensive analyses have definitely shown activation of mTOR pathway in both experimental and human sporadic NETs. Upstream regulators of mTOR (PTEN and TSC2) have been found mutated in sporadic pNETs. Activation of mTOR pathways in NETs is already demonstrated by expression profiles analysis that revealed downregulation of TSC2 gene and alterations of TSC2 and PTEN protein expression in the vast majority of well-differentiated tumors. Moreover, a global microRNA expression analysis revealed the overexpression, in highly aggressive tumors, of a microRNA (miR-21) that targets PTEN reducing its expression and therefore leading to mTOR activation as well. Overall, these clues have furnished the rationale for the use of mTOR inhibitors the treatment of pNETs. With the recent approval of Everolimus (mTOR-targeted drug) for the treatment of advanced pNETs, this paradigm has been effectively translated into the clinical setting. In this review, we discuss mTOR pathway involvement in NETs, the clinical evidence supporting the use of mTOR inhibitors in cancer treatment, and the current clinical issues that remain to be elucidated to improve patient management.

Profiling mTOR pathway in neuroendocrine tumors

The serine/threonine kinase mammalian target of rapamycin (mTOR) plays a central role in regulating critical cellular processes such as growth, proliferation, and protein synthesis. The study of cancer predisposing syndromes within which neuroendocrine tumors (NETs) may arise has furnished clues on the involvement of mTOR pathway in sporadic diseases so far. Recent comprehensive analyses have definitely shown activation of mTOR pathway in both experimental and human sporadic NETs. Upstream regulators of mTOR (PTEN and TSC2) have been found mutated in sporadic pNETs. Activation of mTOR pathways in NETs is already demonstrated by expression profiles analysis that revealed downregulation of TSC2 gene and alterations of TSC2 and PTEN protein expression in the vast majority of well-differentiated tumors. Moreover, a global microRNA expression analysis revealed the overexpression, in highly aggressive tumors, of a microRNA (miR-21) that targets PTEN reducing its expression and therefore leading to mTOR activation as well. Overall, these clues have furnished the rationale for the use of mTOR inhibitors the treatment of pNETs. With the recent approval of Everolimus (mTOR-targeted drug) for the treatment of advanced pNETs, this paradigm has been effectively translated into the clinical setting. In this review, we discuss mTOR pathway involvement in NETs, the clinical evidence supporting the use of mTOR inhibitors in cancer treatment, and the current clinical issues that remain to be elucidated to improve patient management.

Molecular pathology and genetics of pancreatic endocrine tumours

Pancreatic neuroendocrine tumours (PETs) are the second most frequent pancreatic neoplasms. Their poor chemosensitivity, high rate of metastatic disease and relatively long survival make PETs an ideal field to be explored for novel therapies based on specific molecular changes. PETs are generally sporadic but can also arise within hereditary syndromes, such as multiple endocrine neoplasia type 1, von Hippel-Lindau, neurofibromatosis type 1 and tuberous sclerosis complex, which represent a model for sporadic cases too. Among allelic imbalances, main genomic changes involve gain of 17q, 7q and 20q and loss of 11q, 6q and 11p, which identify regions of putative candidate oncogenes or tumour suppressor genes (TSGs), respectively, sometime with potential prognostic significance. Overexpression of Src-like kinases and cyclin D1 (CCND1) oncogene has been described. As for TSGs, P53 (TP53), DPC4/SMAD4 and RB (RB1) are not implicated in PET tumorigenesis, while for p16INK4a (CDKN2A), TIMP3, RASSF1A and hMLH1, more data are available, suggesting a role for methylation as a silencing mechanism. In the last decade, gene expression profile studies, analysis of microRNAs and, more recently, large-scale mutational analysis have highlighted commonly altered molecular pathways in the pathology of PETs. The roles of the mammalian target of rapamycin pathway, and its connection with Src kinases, and the activity of a number of tyrosine kinase receptors seem to be pivotal, as confirmed by the results of recent clinical trials with targeted agents. Mutations of DAXX and ATRX are common and related to altered telomeres but not to prognosis.

Conundrums and Caveats in Neuroendocrine Tumors of the Pancreas

Pancreatic neuroendocrine tumors (Pan-NETs) are the second most common epithelial neoplasm of the pancreas after ductal adenocarcinoma. They can be clinically defined as functional, nonfunctional, and hereditary. This review addresses typical and atypical pathologic features of Pan-NETs, with a focus on practical issues involved in differential diagnosis, immunohistochemical work-up, intraoperative frozen section interpretation, sources of diagnostic errors, and classification. The diagnosis of a Pan-NET requires analysis of all available clinical and radiographic information and pathologic characteristics of the tumor, and it is crucial to understand the clinical impact of the pathologic interpretation.

The archaic distinction between functioning and nonfunctioning neuroendocrine neoplasms is no longer clinically relevant

BACKGROUND

Neuroendocrine neoplasms (NENs) are increasing in incidence and prevalence. This reflects greater clinical awareness, effective imaging, and increasing pathological diagnostic recognition. Although the identification and treatment of clinical neuroendocrine syndromes are established, there is confusion when a NEN has no discernible clinical symptoms.

DISCUSSION

Nonfunctional tumors are usually diagnosed incidentally and at a later stage largely because either they do not secrete a bioactive product or do so, but in a form that is either inactive or in quantities that have no discernible effect. Nevertheless, the histopathology is indistinguishable from functional NENs, and tumors exhibit somatostatin receptor expression, and positive immunohistochemistry for neuroendocrine cell markers (CgA, NSE/synaptophysin). Similarly, their rates of growth and metastatic behavior are, like other NENs, predictably based on staging and grading (mitotic rate and Ki67 expression). Both types are diagnosed biochemically (CgA) and by imaging in an identical fashion with computed tomography, magnetic resonance imaging, somatostatin receptor scintigraphy, and endoscopic ultrasound. NENs, irrespective of function or bioactive secretory profile, respond with equal efficacy to the same regimen of surgery or antitumor drugs (e.g., somatostatin analogs with or without tyrosine kinase inhibitors/antiangiogenics or cytotoxics) depending on grade. Given the efficacy of somatostatin analogs in increasing progression free survival, nonfunctional NENs should be managed identically to symptomatic NENs. The consideration of NENs as functional or nonfunctional is an archaic clinical concept that should be discarded since the tumors are indistinguishable at a cellular, biological, and morphological level. All current evidences indicate that their diagnosis and treatment should follow the same common principles.

Dysregulation of the cell cycle and chromosomal imbalances in juxtaglomerular cell tumors - a comparative study with endocrine tumors of the pancreas

Two juxtaglomerular cell tumors (JGCTs) were investigated in comparison with 14 endocrine tumors of the pancreas (ETPs), focusing on the cell cycle, apoptosis, and cytogenetic changes. JGCTs revealed nuclear accumulation of Cyclin D(1), together with the cyclin-dependent kinase inhibitors p21(Cip1/Waf1) and p27(Kip1). In contrast, no accumulation of Cyclin D(3), p53, p16(INK4a), or Mdm-2 was seen. Bcl-2 protein was intensively, but Rb only moderately, expressed. This immunoreactive profile was not found in the ETPs, which were negative for Bcl-2, p27(Kip1), p21(Cip1/Waf1), and - with one exception - for Cyclin D(1) (1/14) but expressed Cyclin D(3) in 7/14 cases. JGCTs displayed characteristic genetic alterations with combined losses of chromosomes 9, 11, 15, and 21 and gains of chromosome 18. In contrast, no characteristic pattern of genetic alterations was found in ETPs. In both, the amount of chromosomal aberrations correlated with tumor size. In small ETPs and JGCTs, genetic losses dominated over gains of chromosomes, whereas in large/malignant ETPs, gains and losses were equally affected. Thus, JGCTs represent a special type of renal endocrine neoplasm characterized by deregulation of cell cycle components and a typical profile of chromosomal aberrations. Since only two JCTs were investigated, further studies for validation of these results are, however, necessary.

DAXX/ATRX, MEN1, and mTOR pathway genes are frequently altered in pancreatic neuroendocrine tumors

Pancreatic neuroendocrine tumors (PanNETs) are a rare but clinically important form of pancreatic neoplasia. To explore the genetic basis of PanNETs, we determined the exomic sequences of 10 nonfamilial PanNETs and then screened the most commonly mutated genes in 58 additional PanNETs. The most frequently mutated genes specify proteins implicated in chromatin remodeling: 44% of the tumors had somatic inactivating mutations in MEN1, which encodes menin, a component of a histone methyltransferase complex, and 43% had mutations in genes encoding either of the two subunits of a transcription/chromatin remodeling complex consisting of DAXX (death-domain-associated protein) and ATRX (α thalassemia/mental retardation syndrome X-linked). Clinically, mutations in the MEN1 and DAXX/ATRX genes were associated with better prognosis. We also found mutations in genes in the mTOR (mammalian target of rapamycin) pathway in 14% of the tumors, a finding that could potentially be used to stratify patients for treatment with mTOR inhibitors.

Prognostic factors in gastrointestinal endocrine tumors

The gastrointestinal endocrine tumors are neoplastic lesions with often elusive malignant clinical behavior. The current WHO classification attempted to define a more effective approach by introducing the concepts of cell differentiation and site-specific malignancy, as well as specific criteria for carcinoma definition. WHO clinicopathological correlations embed the prognostic features: degree of cell differentiation, angioinvasion, proliferation fraction as assessed by mitotic index and Ki67, size, and functional activity. Other prognostic variables have been recognized, most of which related to specific biological features of neuroendocrine cancer cells. Nonetheless, the presence of liver or distant metastases are the prognostic variables ultimately determining the patients' fate in terms of survival and/or therapy response. A recent proposal of tumor grading and tumor, nodes, and metastases (TNM) staging aims at a simple and practical system for patients stratification. Application of such proposal should be implemented in routine clinical practice.