Multiple allelic deletions and intratumoral genetic heterogeneity in men1 pancreatic tumors

Malignant insulinoma: Can we predict the long-term outcomes?

Insulinomas are the most frequent type of functional pancreatic neuroendocrine tumors with a variety of neuroglycopenic and autonomic symptoms and well-defined diagnostic criteria; however, prediction of their clinical behavior and early differentiation between benign and malignant lesions remain a challenge. The comparative studies between benign and malignant cases are limited, suggesting that short clinical history, early hypoglycemia during fasting, high proinsulin, insulin, and C-peptide concentrations raise suspicion of malignancy. Indeed, malignant tumors are larger with higher mitotic count and Ki-67 proliferative activity, but there are no accurate histological criteria to distinguish benign from malignant forms. Several signaling pathways have been suggested to affect the pathophysiology and behavior of insulinomas; however, our knowledge is limited, urging a further understanding of molecular genetics. Therefore, there is a need for the identification of reliable markers of metastatic disease that could also serve as therapeutic targets in patients with malignant insulinoma. This opinion review reflects on current gaps in diagnostic and clinical aspects related to the malignant behavior of insulinoma.

Pancreatic Neuroendocrine Tumors: Molecular Mechanisms and Therapeutic Targets

Pancreatic neuroendocrine tumors (pNETs) are unique, slow-growing malignancies whose molecular pathogenesis is incompletely understood. With rising incidence of pNETs over the last four decades, larger and more comprehensive 'omic' analyses of patient tumors have led to a clearer picture of the pNET genomic landscape and transcriptional profiles for both primary and metastatic lesions. In pNET patients with advanced disease, those insights have guided the use of targeted therapies that inhibit activated mTOR and receptor tyrosine kinase (RTK) pathways or stimulate somatostatin receptor signaling. Such treatments have significantly benefited patients, but intrinsic or acquired drug resistance in the tumors remains a major problem that leaves few to no effective treatment options for advanced cases. This demands a better understanding of essential molecular and biological events underlying pNET growth, metastasis, and drug resistance. This review examines the known molecular alterations associated with pNET pathogenesis, identifying which changes may be drivers of the disease and, as such, relevant therapeutic targets. We also highlight areas that warrant further investigation at the biological level and discuss available model systems for pNET research. The paucity of pNET models has hampered research efforts over the years, although recently developed cell line, animal, patient-derived xenograft, and patient-derived organoid models have significantly expanded the available platforms for pNET investigations. Advancements in pNET research and understanding are expected to guide improved patient treatments.

ARMC5 Alterations in Patients With Sporadic Neuroendocrine Tumors and Multiple Endocrine Neoplasia Type 1 (MEN1)

CONTEXT

Adrenal lesions are frequent among patients with sporadic neuroendocrine tumors (spNETs) or multiple endocrine neoplasia type 1 (MEN1). Armadillo repeat-containing 5 (ARMC5)-inactivating variants cause adrenal tumors and possibly other neoplasms.

OBJECTIVE

The objective of this work is to investigate a large cohort spNETs or MEN1 patients for changes in the ARMC5 gene.

PATIENTS AND METHODS

A total of 111 patients, 94 with spNET and 17 with MEN1, were screened for ARMC5 germline alterations. Thirty-six tumors (18 spNETs and 18 MEN1 related) were collected from 20 patients. Blood and tumor DNA samples were genotyped using Sanger sequencing and microsatellite markers for chromosomes. ARMC5 and MEN1 expression were assessed by immunohistochemistry.

RESULTS

In 76 of 111 (68.4%) patients, we identified 16 different ARMC5 germline variants, 2 predicted as damaging. There were no differences in the prevalence of ARMC5 variants depending on the presence of MEN1-related adrenal lesions. Loss of heterozygosity (LOH) at chromosome 16p and ARMC5 germline variants were present together in 23 or 34 (67.6%) tumors; in 7 of 23 (30.4%) their presence led to biallelic inactivation of the ARMC5 gene. The latter was more prevalent in MEN1-related tumors than in spNETs (88.9% vs 38.9%; P = .005). LOH at the chromosome 16p (ARMC5) and 11q (MEN1) loci coexisted in 16/18 MEN1-related tumors, which also expressed lower ARMC5 (P = .02) and MEN1 (P = .01) proteins compared to peritumorous tissues.

CONCLUSION

Germline ARMC5 variants are common among spNET and MEN1 patients. ARMC5 haploinsufficiency or biallelic inactivation in spNETs and MEN1-related tumors suggests that ARMC5 may have a role in modifying the phenotype of patients with spNETs and/or MEN1 beyond its known role in macronodular adrenocortical hyperplasia.

Gene expression profiling revealed MCM3 to be a better marker than Ki67 in prognosis of invasive ductal breast carcinoma patients

Invasive ductal carcinoma (IDC) is the most common breast cancer. Our study used gene microarray data to select differentially expressed genes between normal and IDC mammary tissues. From these, we selected genes related to the proliferation of tumor cells and compared their prognostic value with known biomarker Ki67 for IDC. Analysis of publicly available Gene Expression Omnibus (GEO) data revealed 24 differentially expressed genes (DEGs) in normal and 31 DEGS in IDC tissues that were used for further analyses. Gene chip analysis software was used to identify DEGs. DEG profiles were confirmed using quantitative PCR (qPCR). DEG functions where shown to be related to cell proliferation. We confirmed MCM3 expression using immunohistochemical staining in 45 IDC patients. The relationship between MCM3 expression and survival was investigated using Kaplan-Meier survival curves and Cox proportional hazard regression models. A total of 1307 differentially expressed genes were identified between IDC and normal tissues, which were enriched in 32 Gene Ontology (GO) terms and 9 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. qPCR demonstrated that both COL1A1 and MCM3 were significantly up-regulated in IDC tissues, of which only MCM3 was related to cell proliferation. Ki67 is closely associated with the tumor grade, ER status, PR status and HER2 status, while MCM3 was shown to relate to tumor size, lymph node, and PR status. There was significant association between survival and MCM3, but not for Ki67. High MCM3 expression demonstrated statistically significant associations with poor prognosis in IDC patients. Findings from the gene microarray data analysis confirmed that MCM3 is associated with the response to cell proliferation. MCM3 represents a better proliferation marker than Ki67 making it a valuable prognostic tool that is independent of ER and HER2 status.

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.

Liver metastases of small intestine neuroendocrine tumors: Ki-67 heterogeneity and World Health Organization grade discordance with primary tumors

OBJECTIVES

We examined Ki-67 heterogeneity within single and between synchronous liver metastases of small intestine neuroendocrine tumors.

METHODS

There were 27 patients (10 men and 17 women) with two or more liver metastases. The Ki-67 index was used to classify the tumors into World Health Organization grade 1, 2, or 3. The association between Ki-67 heterogeneity and tumor size of liver metastases was analyzed. Correlation of tumor grade with patient survival was also evaluated.

RESULTS

Primary tumors from 20 patients were graded, including 17 grade 1 and three grade 2. A total of 188 liver metastases were resected, including 122 (65%) grade 1, 47 (25%) grade 2, and 19 (10%) grade 3. The highest tumor grade was grade 1 in 10 (37%), grade 2 in nine (33%), and grade 3 in eight (30%) patients. Patients with one or more grade 3 liver lesions had a shorter progression-free survival compared with those with grade 1/2 tumors (P < .001). A positive association was found between tumor size and Ki-67 index (P = .04), as well as between tumor size and intratumoral Ki-67 heterogeneity (P < .001).

CONCLUSIONS

Intratumoral and intertumoral Ki-67 heterogeneity is common and positively correlated with tumor size. The presence of one or more grade 3 liver lesions predicts a worse prognosis.

MEN1 is a melanoma tumor suppressor that preserves genomic integrity by stimulating transcription of genes that promote homologous recombination-directed DNA repair

Multiple endocrine neoplasia type 1 is a familial cancer syndrome resulting from loss-of-function mutations in the MEN1 gene. We previously identified the tumor suppressor MEN1 as a gene required for oncogene-induced senescence in melanocytes, raising the possibility that MEN1 is a melanoma tumor suppressor. Here we show that MEN1 expression is lost in a high percentage of human melanomas and melanoma cell lines. We find that melanocytes depleted of MEN1 are deficient in homologous recombination (HR)-directed DNA repair, which is accompanied by increased nonhomologous end-joining activity. Following DNA damage, MEN1 levels increase as a result of phosphorylation by the DNA damage kinase ATM/ATR. Most importantly, we show that MEN1 functions by directly stimulating the transcription of several genes, including BRCA1, RAD51, and RAD51AP1, that encode proteins involved in HR. MEN1 and its coactivator, the mixed-lineage leukemia histone methyltransferase, are recruited to the BRCA1, RAD51, and RAD51AP1 promoters by estrogen receptor 1, resulting in increased histone H3-lysine 4 trimethylation and transcription. Collectively, our results indicate that MEN1 is a melanoma tumor suppressor that functions by stimulating the transcription of genes involved in HR-directed DNA repair.

Pancreatic endocrine neoplasms: a current update on genetics and imaging

Pancreatic endocrine neoplasms are rare pancreatic tumours that may occur sporadically or as part of inherited syndromes such as multiple endocrine neoplasia-1 syndrome, von Recklinghausen disease, von Hippel-Lindau syndrome and tuberous sclerosis complex. Recent advances in the genetics and pathology of hereditary syndromes have provided valuable insights into the pathophysiology and biology of sporadic pancreatic endocrine neoplasms. Evolving molecular data on the biology of these neoplasms have the potential for diagnostic, therapeutic and prognostic use.

MEN1 and FANCD2 mediate distinct mechanisms of DNA crosslink repair

Cells mutant for multiple endocrine neoplasia type I (MEN1) or any of the Fanconi anemia (FA) genes are hypersensitive to the killing effects of crosslinking agents, but the precise roles of these genes in the response to interstrand crosslinks (ICLs) are unknown. To determine if MEN1 and the FA genes function cooperatively in the same repair process or in distinct repair processes, we exploited Drosophila genetics to compare the mutation frequency and spectra of MEN1 and FANCD2 mutants and to perform genetic interaction studies. We created a novel in vivo reporter system in Drosophila based on the supF gene and showed that MEN1 mutant flies were extremely prone to single base deletions within a homopolymeric tract. FANCD2 mutants, on the other hand, had a mutation frequency and spectrum similar to wild type using this assay. In contrast to the supF results, both MEN1 and FANCD2 mutants were hypermutable using a different assay based on the lats tumor suppressor gene. The lats assay showed that FANCD2 mutants had a high frequency of large deletions, which the supF assay was not able to detect, while large deletions were rare in MEN1 mutants. Genetic interaction studies showed that neither overexpression nor loss of MEN1 modified the ICL sensitivity of FANCD2 mutants. The strikingly different mutation spectra of MEN1 and FANCD2 mutants together with lack of evidence for genetic interaction between these genes indicate MEN1 plays an essential role in ICL repair distinct from the Fanconi anemia genes.

In search of tumor suppressing functions of menin

Human hereditary tumor syndromes serve as an ideal model for studying molecular pathways regulating tumorigenesis. Multiple endocrine neoplasia type 1 (MEN1), a human familial tumor syndrome, results from mutations in the Men1 gene. Men1 encodes a novel tumor suppressor, menin, of unknown biochemical function. Recently, significant progress has been made in identifying menin as a regulator of gene transcription, cell proliferation, apoptosis, and genome stability, leading to a new model of understanding menin's tumor-suppressing function. These findings suggest that menin's diverse functions depend on its association with chromatin and its control over gene transcription. This knowledge will likely be translated into new strategies to improve therapeutic interventions against MEN1 and other related cancers.

Surgery of resectable nonfunctioning neuroendocrine pancreatic tumors

Nonfunctioning neuroendocrine pancreatic tumors (NFNEPTs) comprise about one-third of pancreatic endocrine tumors. Based on immunohistochemistry, nonfunctioning tumors are difficult to distinguish from functioning ones; therefore the final diagnosis is basically the result of a synopsis of pathology and clinical data. Owing to their incapacity to produce hormone-dependent symptoms, NFNEPTs are detected incidentally or because of uncharacteristic symptoms resulting from local or distant growth. About two-thirds of NFNEPTs are located in the pancreatic head, so jaundice may be a late symptom of this tumor. Modern diagnostic procedures are best applied by a stepwise approach: first endoscopic ultrasonography and computed tomography/magnetic resonance imaging followed by somatostatin receptor scintigraphy or positron emission tomography (or both). Due to significant false-positive and false-negative findings, for decision-making the latter should be confirmed by a second imaging modality. Regarding indications for surgery and the surgical approach to the pancreas, three pancreatic manifestations of NFNEPTs can be distinguished: (1) solitary benign non-multiple endocrine neoplasia type 1 (non-MEN-1); (2) multiple benign MEN-1; and (3) malignant NFNEPTs. Reviewing the literature and including our experience with 18 NFNEPTs (8 benign, 10 malignant) reported here, the following conclusions can be drawn: (1) Solitary benign non-MEN-1 NFNEPTs can be removed by enucleation or by pancreas-, spleen-, and duodenum-preserving techniques in most cases. The choice of surgical technique depends on the location and site of the tumor and its anatomic relation to the pancreatic duct. (2) With multiple benign MEN-1 NFNEPTs, because of the characteristics of the underlying disease a preferred, more conservative concept (removal of only macrolesions) competes with a more radical procedure (left pancreatic resection with enucleation of head macrolesions). Further studies are necessary to clarify the best way to balance quality of life (by preserving organ function) with growth control of potentially malignant tumors in the pancreas. (3) Malignant NFNEPTs comprise more than half of all NFNEPTs. Few studies have analyzed treatment strategies for localized or metastatic tumors. Whereas radical (including multivisceral) resection of tumors without distant metastases is widely accepted, the indication for radical surgery on metastasizing tumors has been questioned, as radical removal of the primary tumor may fail to increase survival. Adjuvant regimens in these tumor stages are mandatory and should be further optimized.

Direct binding of DNA by tumor suppressor menin

Menin is a tumor suppressor that is mutated in patients with multiple endocrine neoplasia type I (MEN1), an inherited tumor-prone syndrome. Because there is no obvious conserved structural domain in menin that suggests a biochemical function, little is known as to how menin suppresses tumorigenesis. Although menin interacts with a variety of nuclear proteins including transcription factors, it is unknown whether menin itself can directly bind DNA. Here we show that menin directly binds to double-stranded DNA. It also binds a variety of DNA structures, including Y-structures, branched structures, and 4-way junction structures. The COOH terminus of menin mediates binding to DNA, but MEN1 disease-derived mutations in the COOH terminus abolish the ability of menin to bind DNA. Importantly, these MEN1 disease-related menin mutants also fail to repress cell proliferation as well as cell cycle progression at the G2/M phase. Furthermore, detailed mutagenesis studies indicate that positively charged residues in two nuclear localization signals mediate direct DNA binding as well as repression of cell proliferation. Collectively, these results demonstrate, for the first time, a novel biochemical activity of menin, binding to DNA, and link its DNA binding to the regulation of cell proliferation.