Expression of PTEN and mTOR in pancreatic neuroendocrine tumors

Expression of mTOR in normal and pathological conditions

The mechanistic/mammalian target of rapamycin (mTOR), a protein discovered in 1991, integrates a complex pathway with a key role in maintaining cellular homeostasis. By comprising two functionally distinct complexes, mTOR complex 1 (mTORC1) and mTORC2, it is a central cellular hub that integrates intra- and extracellular signals of energy, nutrient, and hormone availability, modulating the molecular responses to acquire a homeostatic state through the regulation of anabolic and catabolic processes. Accordingly, dysregulation of mTOR pathway has been implicated in a variety of human diseases. While major advances have been made regarding the regulators and effectors of mTOR signaling pathway, insights into the regulation of mTOR gene expression are beginning to emerge. Here, we present the current available data regarding the mTOR expression regulation at the level of transcription, translation and mRNA stability and systematize the current knowledge about the fluctuations of mTOR expression observed in several diseases, both cancerous and non-cancerous. In addition, we discuss whether mTOR expression changes can be used as a biomarker for diagnosis, disease progression, prognosis and/or response to therapeutics. We believe that our study will contribute for the implementation of new disease biomarkers based on mTOR as it gives an exhaustive perspective about the regulation of mTOR gene expression in both normal and pathological conditions.

Tumour Heterogeneity and the Consequent Practical Challenges in the Management of Gastroenteropancreatic Neuroendocrine Neoplasms

Tumour heterogeneity is a common phenomenon in neuroendocrine neoplasms (NENs) and a significant cause of treatment failure and disease progression. Genetic and epigenetic instability, along with proliferation of cancer stem cells and alterations in the tumour microenvironment, manifest as intra-tumoural variability in tumour biology in primary tumours and metastases. This may change over time, especially under selective pressure during treatment. The gastroenteropancreatic (GEP) tract is the most common site for NENs, and their diagnosis and treatment depends on the specific characteristics of the disease, in particular proliferation activity, expression of somatostatin receptors and grading. Somatostatin receptor expression has a major role in the diagnosis and treatment of GEP-NENs, while Ki-67 is also a valuable prognostic marker. Intra- and inter-tumour heterogeneity in GEP-NENS, however, may lead to inaccurate assessment of the disease and affect the reliability of the available diagnostic, prognostic and predictive tests. In this review, we summarise the current available evidence of the impact of tumour heterogeneity on tumour diagnosis and treatment of GEP-NENs. Understanding and accurately measuring tumour heterogeneity could better inform clinical decision making in NENs.

The Expression of Autophagy-Associated Genes Represents a Valid Footprint for Aggressive Pancreatic Neuroendocrine Neoplasms

Pancreatic neuroendocrine neoplasms (pNEN) are rare and heterogeneous tumors. Previous investigations have shown that autophagy can be a target for cancer therapy. This study aimed to determine the association between the expression of autophagy-associated gene transcripts and clinical parameters in pNEN. In total, 54 pNEN specimens were obtained from our human biobank. The patient characteristics were retrieved from the medical record. RT-qPCR was performed to assess the expression of the autophagic transcripts BECN1, MAP1LC3B, SQSTM1, UVRAG, TFEB, PRKAA1, and PRKAA2 in the pNEN specimens. A Mann-Whitney U test was used to detect differences in the expression of autophagic gene transcripts between different tumor characteristics. This study showed that G1 sporadic pNEN have a higher expression of autophagic genes compared to G2. Lymphatic and distant metastasis occurred significantly more often in pNEN with a decreased expression of the autophagic genes. Within sporadic pNEN, the insulinomas express higher levels of autophagic transcripts than gastrinomas and non-functional pNEN. MEN1-associated pNEN show a higher expression of autophagic genes than sporadic pNEN. In summary, a decreased expression of autophagic transcripts distinguishes metastatic from non-metastatic sporadic pNEN. The significance of autophagy as a molecular marker for prognosis and therapy decisions needs to be further investigated.

Effect of adenovirus-mediated overexpression of PTEN on brain oxidative damage and neuroinflammation in a rat kindling model of epilepsy

Background:

Epilepsy is a chronic and severe neurological disorder. Phosphatase and tensin homolog deleted on chromosome ten (PTEN)-deficient mice exhibit learning and memory deficits and spontaneous epilepsy. The aim of this study was to investigate the role of PTEN in brain oxidative damage and neuroinflammation in a rat model of epilepsy.

Methods:

An adenovirus (Ad)-PTEN vector was constructed, and status epilepticus (SE) was induced in 41 model rats using lithium chloride-pilocarpine. Thirty-six SE rats were then allocated into the Ad-PTEN, Ad-LacZ, and SE groups, those were administered intracerebroventricular injections of Ad-PTEN, Ad-enhanced green fluorescent protein, and phosphate buffer saline, respectively. The normal group was comprised of healthy Sprague-Dawley rats. Nissl staining was conducted to evaluate neuronal damage, and immunohistochemistry was conducted to observe the morphology of cells in the hippocampal CA1 region and the distribution of ionized calcium-binding adaptor molecule 1 (Iba1) and ED1 (rat homologue of human CD68). Levels of apoptosis-related proteins, inflammatory-related factors, and oxidative stress-related markers (reactive oxygen species [ROS], glutathione [GSH], superoxide dismutase [SOD], and malondialdehyde [MDA]) were measured. Comparisons between multiple groups were conducted using one-way analysis of variance (ANOVA), and pairwise comparisons after ANOVA were conducted using the Tukey multiple comparisons test.

Results:

After SE induction, PTEN expression in the rat brain exhibited a four-fold decrease (P = 0.000) and the expression of both Iba1 and ED1 increased. Furthermore, significant neuronal loss, oxidative damage, and neuroinflammation were observed in the SE rat brain. After intracerebroventricular injection of Ad-PTEN, PTEN expression exhibited a three-fold increase (P = 0.003), and the expression of both Iba1 and ED1 decreased. Additionally, neurons were restored and neuronal apoptosis was inhibited. Furthermore, ROS and MDA levels decreased, GSH level and SOD activity increased, and neuroinflammation was reduced.

Conclusion:

Our study demonstrated that brain oxidative damage and neuroinflammation in SE rats were ameliorated by intracerebroventricular injection of Ad-PTEN.

Large Cell Neuroendocrine Carcinoma Shares Similarity with Small Cell Carcinoma on the Basis of Clinical and Pathological Features

BACKGROUND

Large cell neuroendocrine carcinoma (LCNEC) was categorized into pulmonary neuroendocrine tumors (NETs) according to the World Health Organization classification guideline. However, LCNEC patients often received the chemotherapy regimens similar to non-small cell lung carcinoma (NSCLC) in advanced stage and the therapeutic effect was unsatisfactory. Therefore, this study aimed to investigate the hidden clinical features, prognosis and immunoprofile of the LCNEC, compared with carcinoid and SCLC, to explore whether LCNEC shares similarity with SCLC and potential treatment approaches could be revealed.

METHODS

One hundred seventeen pulmonary NETs cases were retrospectively retrieved in this study. The Kaplan-Meier estimator was employed to draw survival curves. Immunohistochemistry was applied to detect NET-related markers expression.

RESULTS

In clinical features, compared with carcinoid, LCNEC patients were older, more commonly in male and advanced stage. The parallel phenomena were also found in the high-grade subgroup when compared with the low- to intermediate-grade one. In survival analysis, the 5-year overall survival of LCNECs was 59.1%, which was poorer than that of carcinoids, but better than that of SCLCs. Immunohistochemistry showed that p53 and PTEN functional inactivation, up-regulation of CD117 expression, down-regulation of SSR2A and SSR5 expression were commonly involved in LCNECs when compared with carcinoids, or in the high-grade subgroup when compared with the low- to intermediate-grade one. However, no significant difference was found in the comparison between LCNECs and SCLCs, or NSCLCs and SCLCs.

CONCLUSION

In clinical features, survival and immunoprofile, LCNEC showed more similarity with SCLC rather than carcinoid, which might guide novel therapy for pulmonary NETs.

Bexarotene inhibits the viability of non-small cell lung cancer cells via slc10a2/PPARγ/PTEN/mTOR signaling pathway

Background

Thirty to 40 % of non-small cell lung cancer (NSCLC) patients developed higher hypertriglyceridemia in the process of treatment with bexarotene. And bioinformatics studies discovered that the expression of slc10a2 was increased in high-grade hypertriglyceridemia patients. So, we will explore the mechanism which may involve in this process.

Methods

We constructed slc10a2 overexpressed A549 cells and H1299 cells as cell models, normal A549 cells and H1299 cells as control. Then we explored the effects of slc10a2 on A549 cells and H1299 cells behaviors, including proliferation, invasion and apoptosis. The expression of apoptotic related genes and anti-cancer genes also been detected.

Results

We found that the proliferation and migration were inhibited and the apoptosis of NSCLC cells was accelerated by bexarotene. In addition, overexpressed slc10a2 in NSCLC cells can further suppress the proliferation and migration, and promote apoptosis under the treatment of bexarotene. On the contrary, the opposite results were obtained after slc10a2 gene was silenced in NSCLC cells treated with bexarotene. Moreover, the expression of caspase 3, caspase 7, PTEN, P21, P53, LKB1, TSC2 were increased and the expression of Bcl-2, cyclin D1, c-FLIP were declined in NSCLC cells and slc10a2 overexpressed NSCLC cells with the treatment of bexarotene, and the opposite situations were seen after slc10a2 gene was silenced in NSCLC cells. The further studies revealed the increased expression of slc10a2 activated the expression of peroxisome proliferator-activated receptor γ (PPARγ), then up-regulated PTEN expression and down-regulated mTOR expression.

Conclusion

These results suggest that bexarotene inhibits the viability of lung cancer cells via slc10a2/PPARγ/PTEN/mTOR signaling pathway.

Electronic supplementary material

The online version of this article (10.1186/s12885-018-4224-x) contains supplementary material, which is available to authorized users.

Determination of Mammalian Target of Rapamycin Hyperactivation as Prognostic Factor in Well-Differentiated Neuroendocrine Tumors

Purpose

To evaluate the role of the activation of mTOR (phosphorylated mTOR, p-mTOR) and the expression SSTR2A and IGF-1R as prognostic factor in well-differentiated neuroendocrine tumors.

Methods

A retrospective study was conducted on data from patients with diagnosis of neuroendocrine tumor originated from pancreas (pNET) or gastrointestinal tract (stomach, appendix, and ileus; GI-NET) made between January 2003 and December 2004 and followed up at our institution. Archival material should be available for revision according to WHO 2010 neuroendocrine tumor classification and for p-mTOR, SSTR2A, and IGF-1R immunostaining, calculating a quantitative score (QS). We evaluated clinical, pathological, and immunohistochemistry features for association with the presence of advanced disease at diagnosis and disease relapse in patients who have undergone radical surgery.

Results

Archival material from 64 patients was analyzed (37 pNETs and 27 GI-NETs). In these patients, G2 grading, low SSTR2A QS, and high p-mTOR QS were associated with advanced disease at diagnosis at multivariate analysis. Risk of recurrence in 49 patients with R0-resected tumors was higher for G2 grading, stage IIIB-IV, low IGF-1R QS, and high p-mTOR QS at univariate analysis.

Conclusions

With the limits of retrospective data, activation of m-TOR is correlated with advanced disease at diagnosis and with shorter disease-free survival after R0 resection. Validation through prospective studies is needed.

The regulatory role of aberrant Phosphatase and Tensin Homologue and Liver Kinase B1 on AKT/mTOR/c-Myc axis in pancreatic neuroendocrine tumors

Pancreatic neuroendocrine tumor (pNET) is an uncommon type of pancreatic neoplasm. Low Phosphatase and Tensin Homologue (PTEN) expression and activation of the mechanistic target of rapamycin (mTOR) pathway have been noted in pNETs, and the former is associated with poor survival in pNET patients. Based on the results of the RADIANT-3 study, everolimus, an oral mTOR inhibitor, has been approved to treat advanced pNETs. However, the exact regulatory mechanism for the mTOR pathway in pNETs remains largely unknown. PTEN and liver kinase B1 (LKB1) are well-known for their regulatory role in the mTOR pathway. We evaluated the expression of PTEN and LKB1 in 21 pNET patients, and low PTEN and LKB1 expression levels were noted in 48% and 24% of the patients, respectively. Loss of PTEN and LKB1 synergistically promoted cell proliferation of pNET, attenuated the sensitivity of cells to mTOR inhibitors and enhanced c-Myc expression, which back-regulated PTEN, AKT, mTOR and its downstream effectors. For pNET cells with low expression levels of PTEN and LKB1, silencing the expression of c-Myc by shRNA reduced their proliferative rate, while adding either c-Myc inhibitor or AMP-activated protein kinase activator reversed their resistance to mTOR inhibitors in vitro and in vivo. Furthermore, high c-Myc expression was subsequently identified in 81% of pNETs, suggesting that up-regulation of c-Myc expression in pNETs may occur through PTEN/LKB1-dependent and PTEN/LKB1-independent regulation. The results delineated the regulation of PTEN and LKB1 on the AKT/mTOR/c-Myc axis and suggested that both c-Myc and mTOR are potential therapeutic targets for pNET.

Phosphatase and tensin homolog (PTEN) is down-regulated in human NK/T-cell lymphoma and corrects with clinical outcomes

Nasal-type natural killer/T-cell (NK/T-cell) lymphoma is a more aggressive sub-group of non-Hodgkin lymphoma, which is more common in Asia. The phosphatase and tensin homolog (PTEN) was originally discovered as a candidate tumor suppressor mutated and lost in various cancers. However, its clinical value and role in NK/T-cell lymphoma remain to be further explored. In the present study, we analyzed PTEN protein expression in 60 cases of human NK/T-cell lymphoma tissues and 40 cases of control nasal mucosa tissues specimens by immunohistochemical analysis. As a result, positive rate of PTEN protein expression in NK/T-cell lymphoma tissues (33.3%) is significantly lower than that of control nasal mucosa tissues (85.0%) (P < .01). However, no significant association was found between PTEN protein expression and sex, age, tumor location, clinical staging (Ann Arbor staging), or serum lactate dehydrogenase level (P > .05). Instead, PTEN protein was inversely corrected with Ki-67 expression, indicating a functional role in PTEN in human NK/T-cell lymphoma (P < .05). For clinical outcomes, PTEN positive rate significantly increased in objective response group (CR+PR) (43.5%) compared with SD+PD group (18.9%). Furthermore, overexpression of PTEN contributed to chemotherapy sensitivity to different doses of cisplatin (DDP) in human NK/T-cell lymphoma SNK-6 cells. These results suggest that PTEN may regulate chemotherapy sensitivity of NK/T-cell lymphoma and contribute to clinical outcomes. These findings indicate PTEN to be a potential target anti-tumor therapeutics for NK/T-cell lymphoma.

Biologics in gastrointestinal and pancreatic neuroendocrine tumors

The development of biologic agents has ushered in a new era of precision medicine, opening the door to new therapeutic options designed to intelligently target cancer cells and their promoting factors, while leaving normal cells relatively unharmed. Biologics for the treatment of neuroendocrine tumors (NETs) have followed in the footsteps of regimens targeting pathways upregulated in other cancers, including the vascular endothelial growth factor (VEGF) and the mammalian target of rapamycin (mTOR). Through a number of clinical trials, the mTOR inhibitor everolimus and the receptor tyrosine kinase (RTK) inhibitor sunitinib were recently approved for NETs. Other biologics such as the VEGF-A inhibitor bevacizumab have also demonstrated promising clinical activity in NETs. Interestingly, though trials have demonstrated the efficacy of everolimus and sunitinib in extending progression-free survival (PFS) in NETs, objective response rates (RR) are uniformly low, indicating that the primary effect of these drugs is maintenance of stable disease. Due to the relatively indolent nature of the more common, well-differentiated variety of NETs, stable disease is often a reasonable goal for NET patients. Well-differentiated NETs have been shown to be poor responders to cytotoxic chemotherapy, underlining the important role of biologics in treating and managing NETs and their hormonal symptoms. Ongoing and future trials are investigating a wide variety of biologic compounds in NETs, including other RTK inhibitors, mTOR pathway inhibitors, and immune checkpoint inhibitors. Within this review, we will discuss major trials leading up to the FDA approval of everolimus and sunitinib for NETs, as well as other promising biologics currently under investigation in NET clinical trials.

Critical focus on mechanisms of resistance and toxicity of m-TOR inhibitors in pancreatic neuroendocrine tumors

Pancreatic neuroendocrine tumors (pNETs) are rare neoplasms representing less than 2% of all pancreatic malignancies. The PI3K-AKT-mTOR pathway is often deregulated in pNETs and seems to play a key role in tumorigenesis. Everolimus, an inhibitor of the mTOR pathway, has demonstrated efficacy in the treatment of pNETs. Nevertheless de novo or acquired drug resistance is responsible for disease progression and represents a major obstacle to overcome by clinicians. Blocking the PI3K/AKT/mTOR pathway may cover the supposed main mechanisms of resistance to everolimus. Therefore, BEZ-235, a potent oral dual PI3K/mTOR inhibitor was investigated in clinical trials. Globally more than 250 patients with different types of solid tumors were treated. Two studies were conducted in pNETs with BEZ-235 as single agent. The former was a phase 2 trial conducted in pNETs resistant to everolimus while the latter a randomized trial comparing everolimus and BEZ-235. Unfortunately, both the studies disappointed the expectations and were prematurely halted mainly due to severe toxicity. On this basis we reviewed m-TOR inhibitors in pNETs, focusing on their mechanisms of resistance and toxicity.

Anti-proliferative and anti-secretory effects of everolimus on human pancreatic neuroendocrine tumors primary cultures: is there any benefit from combination with somatostatin analogs?

Therapeutic management of gastroenteropancreatic neuroendocrine tumors (GEP-NETs) is challenging. The mammalian target of rapamycin (mTOR) inhibitor everolimus recently obtained approval from the Food and Drug Administration for the treatment of patients with advanced pancreatic neuroendocrine tumors (pNETs). Despite its promising antitumor efficacy observed in cell lines, clinical benefit for patients is unsatisfactory. The limited therapeutic potential of everolimus in cancer cells has been attributed to Akt activation due to feedback loops relief following mTOR inhibition. Combined inhibition of Akt might then improve everolimus antitumoral effect. In this regard, the somatostatin analog (SSA) octreotide has been shown to repress the PI3K/Akt pathway in some tumor cell lines. Moreover, SSAs are well tolerated and routinely used to reduce symptoms caused by peptide release in patients carrying functional GEP-NETs. We have recently established and characterized primary cultures of human pNETs and demonstrated the anti-proliferative effects of both octreotide and pasireotide. In this study, we aim at determining the antitumor efficacy of everolimus alone or in combination with the SSAs octreotide and pasireotide in primary cultures of pNETs. Everolimus reduced both Chromogranin A secretion and cell viability and upregulated Akt activity in single treatment. Its anti-proliferative and anti-secretory efficacy was not improved combined with the SSAs. Both SSAs did not overcome everolimus-induced Akt upregulation. Furthermore, caspase-dependent apoptosis induced by SSAs was lost in combined treatments. These molecular events provide the first evidence supporting the lack of marked benefit in patients co-treated with everolimus and SSA.

Loss of PTEN Expression Is Associated With High MicroRNA 24 Level and Poor Prognosis in Patients With Tongue Squamous Cell Carcinoma

PURPOSE

The aim of this study was to detect the relationship between phosphatase and tensin homolog deletion on chromosome 10 (PTEN) and microRNA 24 (miR-24) and correlate PTEN expression with important clinical parameters of patients with tongue squamous cell carcinoma (TSCC).

MATERIALS AND METHODS

In this retrospective case series, all TSCC patients treated at Tianjin Medical University Cancer Institute and Hospital between March 2005 and October 2011 were retrospectively reviewed. Demographic information and clinical data (histologic type, clinical stage, tumor differentiation, and so on) were collected. The miR-24 level was detected by quantitative reverse transcription-polymerase chain reaction. The PTEN level was analyzed by immunohistochemistry and quantitative reverse transcription-polymerase chain reaction. Data analyses were performed by Spearman correlation analysis, Pearson χ² test, and paired t test. Kaplan-Meier curves, log-rank analyses, and a Cox proportional hazards model were used to evaluate the prognostic value of PTEN.

RESULTS

A total of 90 patients (aged 59.4 ± 9.5 years, 53 men and 37 women) were identified. Loss of PTEN expression was detected in 27 of 90 tumors (30%)” in both occurrences [corrected]. The PTEN messenger RNA level was negatively correlated with the miR-24 level (r = -0.569, P < .01). PTEN expression also was negatively correlated with the miR-24 level (r = -0.621, P < .01). Furthermore, PTEN expression was significantly lower in cancer tissues than in adjacent normal tissues, and its expression was negatively correlated with clinical stage (P < .01) and positively correlated with differentiation (P < .05) in TSCC patients. In addition, the Kaplan-Meier curve indicated that loss of PTEN expression resulted in poor survival of TSCC patients (P < .01). Multivariate analysis indicated that PTEN expression level and clinical stage may be independent prognostic factors for TSCC patients.

CONCLUSIONS

This study suggested that PTEN expression was negatively correlated with the miR-24 level in TSCC. The loss of PTEN expression may serve as a predictor of unfavorable prognosis for TSCC patients.

Effective PI3K modulators for improved therapy against malignant tumors and for neuroprotection of brain damage after tumor therapy (Review)

Due to the key role in various cellular processes including cell proliferation and cell survival on many cell types, dysregulation of the PI3K/AKT pathway represents a crucial step of the pathogenesis in many diseases. Furthermore, the tumor suppressor PTEN negatively regulates the PI3K/AKT pathway through its lipid phosphatase activity, which is recognized as one of the most frequently deleted and/or mutated genes in human cancer. Given the pervasive involvement of this pathway, the development of the molecules that modulate this PI3K/AKT signaling has been initiated in studies which focus on the extensive effective drug discovery. Consequently, the PI3K/AKT pathway appears to be an attractive pharmacological target both for cancer therapy and for neurological protection necessary after the therapy. A better understanding of the molecular relations could reveal new targets for treatment development. We review recent studies on the features of PI3K/AKT and PTEN, and their pleiotropic functions relevant to the signaling pathways involved in cancer progress and in neuronal damage by the therapy.

Towards a new classification of gastroenteropancreatic neuroendocrine neoplasms

Gastroenteropancreatic neuroendocrine neoplasms (GEP-NENs) constitute a heterogeneous group of tumours associated with variable clinical presentations, growth rates, and prognoses. To improve the management of GEP-NENs, the WHO developed a classification system that enables tumours to be graded based on markers of cell proliferation in biopsy specimens. Indeed, histopathology has been a mainstay in the diagnosis of GEP-NENs, and the WHO grading system facilitates therapeutic decision-making; however, considerable intratumoural heterogeneity, predominantly comprising regional variations in proliferation rates, complicates the evaluation of tumour biology. The use of molecular imaging modalities to delineate the most-aggressive cell populations is becoming more widespread. In addition, molecular profiling is increasingly undertaken in the clinical setting, and genomic studies have revealed a number of chromosomal alterations in GEP-NENs, although the 'drivers' of neoplastic development have not been identified. Thus, our molecular understanding of GEP-NENs remains insufficient to inform on patient prognosis or selection for treatments, and the WHO classification continues to form the basis for management of this disease. Nevertheless, our increasing understanding of the molecular genetics and biology of GEP-NENs has begun to expose flaws in the WHO classification. We describe the current understanding of the molecular characteristics of GEP-NENs, and discuss how advances in molecular profiling measurements, including assays of circulating mRNAs, are likely to influence the management of these tumours.

Ki-67 prognostic and therapeutic decision driven marker for pancreatic neuroendocrine neoplasms (PNENs): A systematic review

BACKGROUND

We systematically evaluate the current evidence regarding Ki-67 as a prognostic factor in pancreatic neuroendocrine neoplasms to evaluate the differences of this marker in primary tumors and in distant metastases as well as the values of Ki-67 obtained by fine needle aspiration and by histology.

METHODS

The literature search was carried out using the MEDLINE/PubMed database, and only papers published in the last 10 years were selected.

RESULTS

The pancreatic tissue suitable for Ki-67 evaluation was obtained from surgical specimens in the majority of the studies. There was a concordance of 83% between preoperative and postoperative Ki-67 evaluation. Pooling the data of the studies which compared the Ki-67 values obtained in both cytological and surgical specimens, we found that they were not related. The assessment of Ki-67 was manual in the majority of the papers considered for this review. In order to eliminate manual counting, several imaging methods have been developed but none of them are routinely used at present. Twenty-two studies also explored the role of Ki-67 utilized as a prognostic marker for pancreatic neuroendocrine neoplasms and the majority of them showed that Ki-67 is a good prognostic marker of disease progression. Three studies explored the Ki-67 value in metastatic sites and one study demonstrated that, in metachronous and synchronous liver metastases, there was no significant variation in the index of proliferation.

CONCLUSIONS

Ki-67 is a reliable prognostic marker for pancreatic neuroendocrine neoplasms.

The spectrum of neuroendocrine tumors: histologic classification, unique features and areas of overlap

Neuroendocrine neoplasms are diverse in terms of sites of origin, functional status, and degrees of aggressiveness. This review will introduce some of the common features of neuroendocrine neoplasms and will explore the differences in pathology, classification, biology, and clinical management between tumors of different anatomic sites, specifically, the lung, pancreas, and prostate. Despite sharing neuroendocrine differentiation and histologic evidence of the neuroendocrine phenotype in most organs, well-differentiated neuroendocrine tumors (WD-NETs) and poorly differentiated neuroendocrine carcinomas (PD-NECs) are two very different families of neoplasms. WD-NETs (grade 1 and 2) are relatively indolent (with a natural history that can evolve over many years or decades), closely resemble non-neoplastic neuroendocrine cells, and demonstrate production of neurosecretory proteins, such as chromogranin A. They arise in the lungs and throughout the gastrointestinal tract and pancreas, but WD-NETs of the prostate gland are uncommon. Surgical resection is the mainstay of therapy, but treatment of unresectable disease depends on the site of origin. In contrast, PD-NECs (grade 3, small cell or large cell) of all sites often demonstrate alterations in P53 and Rb, exhibit an aggressive clinical course, and are treated with platinum-based chemotherapy. Only WD-NETs arise in patients with inherited neuroendocrine neoplasia syndromes (e.g., multiple endocrine neoplasia type 1), and some common genetic alterations are site-specific (e.g., TMPRSS2-ERG gene rearrangement in PD-NECs arising in the prostate gland). Advances in our understanding of the molecular basis of NETs should lead to new diagnostic and therapeutic strategies and is an area of active investigation.

Pathologic Classification of Neuroendocrine Neoplasms

The pathologic classification of neuroendocrine neoplasms has evolved over the past decades, as new understanding of the biological behavior, histologic characteristics, and genetic features have emerged. Nonetheless, many aspects of the classification systems remain confusing or controversial. Despite these difficulties, much progress has been made in determining the features predicting behavior. Genetic findings have helped establish relationships among different types of neuroendocrine neoplasms and revealed potential therapeutic targets. This review summarizes the current approach to the diagnosis, classification, grading, and therapeutic stratification of neuroendocrine neoplasms, with a focus on those arising in the lung and thymus, pancreas, and intestines.

miR-144/451 Promote Cell Proliferation via Targeting PTEN/AKT Pathway in Insulinomas

Insulinoma is the main type of functional pancreatic neuroendocrine tumors. The functional microRNAs (miRNAs) regulating tumor growth and progression in insulinomas are still unknown. We conducted the miRNA expression profile analysis using miRNA quantitative RT-PCR array and identified 114 differentially expressed miRNAs in human insulinomas compared with normal pancreatic islets. Forty-one differentially expressed miRNAs belonged to 7 miRNA families, and 28 miRNAs in 3 of the families localized in the epigenetically regulated imprinted chromosome 14q32 region. We validated the most significant differentially expressed miRNA cluster miR-144/451 in another 8 human normal islet samples and 25 insulinomas. Our data showed that the overexpression of miR-144/451 in mouse pancreatic β-cells promoted cell proliferation by targeting the β-cell regulator phosphatase and tensin homolog deleted on chromosome ten/v-akt murine thymoma viral oncogene homolog pathway and cyclin-dependent kinase inhibitor 2D. Our findings highlight the importance of functional miRNAs in insulinomas.

Successful control of heavily pretreated metastatic gastric cancer with the mTOR inhibitor everolimus (RAD001) in a patient with PIK3CA mutation and pS6 overexpression

Background

Everolimus (RAD001) is an orally administered mTOR inhibitor that is well known for its antitumor efficacy and that has been approved for the treatment of several solid tumors, including renal cell carcinoma. In gastric cancer (GC), despite previous preclinical and phase I/II studies suggesting the promising efficacy of everolimus in previously treated AGC, more recent trials revealed that only certain subsets of patients might benefit from treatment with everolimus.

Case presentation

A 26-year-old man with metastatic gastric cancer with multiple liver lesions was treated with everolimus after failure of 1st-line and 2nd-line chemotherapy. A durable partial response was achieved for over 2 years. After progression from initial everolimus treatment, sequential cytotoxic chemotherapies were tried but failed rapidly. Everolimus was re-tried as salvage chemotherapy (re-treatment), and the patient achieved stable disease for 1 year until his death. Subsequent mutational analysis and immunohistochemical (IHC) staining with the tumor tissues just before re-treatment with everolimus revealed a PIK3CA hotspot mutation and pS6 overexpression in the primary tumor. After two cycles of everolimus re-treatment, the overexpression of pS6 became nearly absent in follow-up IHC staining.

Conclusions

Everolimus monotherapy was satisfactory in a patient with refractory metastatic GC harboring PIK3CA and pS6 aberrations. These molecular alterations might be potential biomarkers that can predict the treatment response of everolimus, particularly in the terms of durable disease control. This case suggests and emphasizes that close evaluation of biomarkers in tumor tissue may be essential for identifying highly favorable groups among various subpopulations with AGC.

Molecular pathogenesis and targeted therapy of sporadic pancreatic neuroendocrine tumors

Over the past few years, knowledge regarding the molecular pathology of sporadic pancreatic neuroendocrine tumors (PNETs) has increased substantially, and a number of targeted agents have been tested in clinical trials in this tumor type. For some of these agents there is a strong biological rationale. Among them, the mammalian target of rapamycin inhibitor Everolimus and the antiangiogenic agent Sunitinib have both been approved for the treatment of PNETs. However, there is lack of knowledge regarding biomarkers able to predict their efficacy, and mechanisms of resistance. Other angiogenesis inhibitors, such as Pazopanib, inhibitors of Src, Hedgehog or of PI3K might all be useful in association or sequence with approved agents. On the other hand, the clinical significance, and potential for treatment of the most common mutations occurring in sporadic PNETs, in the MEN-1 gene and in ATRX and DAXX, remains uncertain. The present paper reviews the main molecular changes occurring in PNETs and how they might be linked with treatment options.

Altered Expression of PTEN and Its Major Regulator MicroRNA-21 in Pulmonary Neuroendocrine Tumors

Background

Phosphatase and tensin homolog on chromosome ten (PTEN) is one of the most frequently inactivated tumor suppressors in various tumor types. MicroRNA-21 (miR-21) may affect tumor progression by post-transcriptional repression of expression of tumor suppressors, such as PTEN. This study was conducted to evaluate the significance of PTEN expression in pulmonary neuroendocrine (NE) tumors and to analyze the relationship between PTEN and miR-21 expressions.

Methods

Expressions of PTEN and miR-21 were investigated by immunohistochemistry and real time reverse transcription-polymerase chain reaction, respectively, in 75 resected pulmonary NE tumors (23 typical carcinoids [TCs], nine atypical carcinoids [ACs], 22 large cell NE carcinomas [LCNECs], and 21 small cell lung carcinomas [SCLCs]).

Results

Loss of PTEN expression was observed in four of 23 TCs (17.4%), four of nine ACs (44.4%), 16 of 22 LCNECs (72.7%) and nine of 21 SCLCs (42.9%) (p=.025). The expression level of miR-21 was significantly higher in high-grade NE carcinomas than in carcinoid tumors (p<.001). PTEN expression was inversely correlated with miR-21 expression (p<.001).

Conclusions

This study suggests that aberrant expression of PTEN in relation to miR-21 may represent an important step in the development and progression of pulmonary NE tumors.