Serotonin pathway in carcinoid syndrome: Clinical, diagnostic, prognostic and therapeutic implications

A case of carcinoid syndrome probably exacerbated by hemodialysis in which prochlorperazine maleate was effective

Carcinoid syndrome is caused by the release of serotonin and other substances, which commonly occurs due to liver metastasis of neuroendocrine tumors. It rarely occurs due to liver metastasis of neuroendocrine carcinoma. We report the case of a patient with liver metastasis of neuroendocrine carcinoma who suffered from acute abdominal pain and diarrhea triggered by hemodialysis. Various differential diagnoses were considered, but we concluded these symptoms to be probably caused by exacerbation of carcinoid syndrome, as the serum 5HIAA level was markedly elevated, and a drug with anti-serotonin activity was effective. Prochlorperazine maleate, which has anti-serotonin activity, was effective for these symptoms, and the patient was able to continue maintenance hemodialysis, which contributed to his quality of life and prognosis. We speculated the mechanism of carcinoid exacerbation was that substances such as serotonin had entered the systemic circulation via the increased extrahepatic shunt of the portal venous blood flow, entering the inferior vena cava and that this condition had been triggered by hemodialysis via the same mechanism as portal systemic encephalopathy.

Gender-related differences in patients with carcinoid syndrome: new insights from an Italian multicenter cohort study

BACKGROUND

The incidence of neuroendocrine neoplasm (NEN) and related carcinoid syndrome (CaS) has increased markedly in recent decades, and women appear to be more at risk than men. As per other tumors, gender may be relevant in influencing the clinical and prognostic characteristics of NEN-associated CS. However, specific data on carcinoid syndrome (CaS) are still lacking.

PURPOSE

To evaluate gender differences in clinical presentation and outcome of CaS.

METHODS

Retrospective analysis of 144 CaS patients from 20 Italian high-volume centers was conducted. Clinical presentation, tumor characteristics, therapies, and outcomes (progression-free survival, PFS, overall survival, OS) were correlated to gender.

RESULTS

Ninety (62.5%) CaS patients were male. There was no gender difference in the site of primary tumor, tumor grade and clinical stage, as well as in treatments. Men were more frequently smokers (37.2%) and alcohol drinkers (17.8%) than women (9.5%, p = 0.002, and 3.7%, p = 0.004, respectively). Concerning clinical presentation, women showed higher median number of symptoms (p = 0.0007), more frequent abdominal pain, tachycardia, and psychiatric disorders than men (53.3% vs 70.4%, p = 0.044; 6.7% vs 31.5%, p = 0.001; 50.9% vs. 26.7%, p = 0.003, respectively). Lymph node metastases at diagnosis were more frequent in men than in women (80% vs 64.8%; p = 0.04), but no differences in terms of PFS (p = 0.51) and OS (p = 0.64) were found between gender.

CONCLUSIONS

In this Italian cohort, CaS was slightly more frequent in males than females. Gender-related differences emerged in the clinical presentation of CaS, as well as gender-specific risk factors for CaS development. A gender-driven clinical management of these patients should be advisable.

Plasma tryptophan pathway metabolites quantified by liquid chromatography-tandem mass spectrometry as biomarkers in neuroendocrine tumor patients

A good and accessible biomarker is of great clinical value in neuroendocrine tumor (NET) patients, especially considering its frequently indolent nature and long-term follow-up. Plasma chromogranin A (CgA) and 5-hydroxyindoleacetic acid (5-HIAA) are currently used as biomarkers in NET, but their sensitivity and specificity are restricted. 5-HIAA is the main metabolite of serotonin, an important neurotransmitter of the tryptophan pathway. The aim of this study is to estabish a sensitive and accurate method for the quantification of tryptophan pathway metabolites in plasma. We further aimed to evaluate its utility as a clinical tool in NET disease. We obtained plasma samples from NET patients and healthy controls recruited from the University Hospital of North Norway, Tromsø. Samples were analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS), and eight metabolites of the tryptophan pathway were quantified. We included 130 NET patients (72/130 small intestinal [SI] NET, 35/130 pancreatic NET, 23/130 other origin) and 20 healthy controls. In the SI-NET group, 26/72 patients presented with symptoms of carcinoid syndrome (CS). We found that combining tryptophan metabolites into a serotonin/kynurenine pathway ratio improved diagnostic sensitivity (92.3%) and specificity (100%) in detecting CS patients from healthy controls compared with plasma 5-HIAA alone (sensitivity 84.6%/specificity 100%). Further, a clinical marker based on the combination of plasma serotonin, 5-HIAA, and 5OH-tryptophan, increased diagnostic capacity identifying NET patients with metastasized disease from healthy controls compared with singular plasma 5-HIAA, serotonin, or CgA. In addition, this marker was positive in 61% of curatively operated SI-NET patients compared with only 10% of healthy controls (p < .001). Our results indicate that simultaneous quantification of several tryptophan metabolites in plasma, using LC-MS/MS, may represent a clinically useful diagnostic tool in NET disease.

The cause-and-effect relationship between gut microbiota abundance and carcinoid syndrome: a bidirectional Mendelian randomization study

Objective

Carcinoid syndrome (CS) commonly results from neuroendocrine tumors. While active substances are recognized as the main causes of the typical symptoms such as diarrhea and skin flush, the cause-and-effect relationship between gut microbiota abundance and CS remains unclear.

Methods

The Single Nucleotide Polymorphisms (SNPs) related to gut microbiota abundance and CS were obtained from the GWAS summary data. The inverse variance weighted (IVW) method was used to assess the causal relationship between gut microbiota abundance and CS. Additionally, the MR-Egger, Weighted Median model, and Weighted model were employed as supplementary approaches. The heterogeneity function of the TwoSampleMR package was utilized to assess whether SNPs exhibit heterogeneity. The Egger intercept and Presso test were used to assess whether SNPs exhibit pleiotropy. The Leave-One-Out test was employed to evaluate the sensitivity of SNPs. The Steiger test was utilized to examine whether SNPs have a reverse causal relationship. A bidirectional mendelian randomization (MR) study was conducted to elucidate the inferred cause-and-effect relationship between gut microbiota abundance and CS.

Results

The IVW results indicated a causal relationship between 6 gut microbiota taxa and CS. Among the 6 gut microbiota taxa, the genus Anaerofilum (IVW OR: 0.3606, 95%CI: 0.1554-0.8367, p-value: 0.0175) exhibited a protective effect against CS. On the other hand, the family Coriobacteriaceae (IVW OR: 3.4572, 95%CI: 1.0571-11.3066, p-value: 0.0402), the genus Enterorhabdus (IVW OR: 4.2496, 95%CI: 1.3314-13.5640, p-value: 0.0146), the genus Ruminiclostridium6 (IVW OR: 4.0116, 95%CI: 1.2711-12.6604, p-value: 0.0178), the genus Veillonella (IVW OR: 3.7023, 95%CI: 1.0155-13.4980, p-value: 0.0473) and genus Holdemanella (IVW OR: 2.2400, 95%CI: 1.0376-4.8358, p-value: 0.0400) demonstrated a detrimental effect on CS. The CS was not found to have a reverse causal relationship with the above 6 gut microbiota taxa.

Conclusion

Six microbiota taxa were found to have a causal relationship with CS, and further randomized controlled trials are needed for verification.

Effective strategies for adequate control of hormonal secretion in functioning neuroendocrine neoplasms

Neuroendocrine neoplasms are a unique form of malignancies as they can be accompanied by specific functioning hormonal syndromes that can impair survival and quality of life in patients. Functioning syndromes are defined by the combination of specific clinical signs and symptoms in combination with inappropriately elevated circulating levels of hormones. Clinicians should remain vigilant for the presence of functioning syndromes in neuroendocrine neoplasm patients at presentation as well as during follow-up. The correct diagnostic work-up should be initiated in cases of clinical suspicion of a neuroendocrine neoplasm-associated functioning syndrome. Management of a functional syndrome includes options from supportive, surgical, hormonal and antiproliferative treatment modalities. Here, we review the patient and tumour characteristics for each functioning syndrome that should be taken into account when deciding the optimum treatment strategy in neuroendocrine neoplasm patients.

Carcinoid Syndrome: Preclinical Models and Future Therapeutic Strategies

Carcinoid syndrome represents a debilitating paraneoplastic disease, caused by the secretion of several substances, occurring in about 10-40% of patients with well-differentiated neuroendocrine tumors (NETs). The main signs and symptoms associated with carcinoid syndrome are flushing, diarrhea, hypotension, tachycardia, bronchoconstriction, venous telangiectasia, dyspnea and fibrotic complications (mesenteric and retroperitoneal fibrosis, and carcinoid heart disease). Although there are several drugs available for the treatment of carcinoid syndrome, the lack of therapeutic response, poor tolerance or resistance to drugs are often reported. Preclinical models are indispensable tools for investigating the pathogenesis, mechanisms for tumor progression and new therapeutic approaches for cancer. This paper provides a state-of-the-art overview of in vitro and in vivo models in NETs with carcinoid syndrome, highlighting the future developments and therapeutic approaches in this field.

Neuroendocrine neoplasms in the context of inherited tumor syndromes: a reappraisal focused on targeted therapies

PURPOSE

Neuroendocrine neoplasms can occur as part of inherited disorders, usually in the form of well-differentiated, slow-growing tumors (NET). The main predisposing syndromes include: multiple endocrine neoplasias type 1 (MEN1), associated with a large spectrum of gastroenteropancreatic and thoracic NETs, and type 4 (MEN4), associated with a wide tumour spectrum similar to that of MEN1; von Hippel-Lindau syndrome (VHL), tuberous sclerosis (TSC), and neurofibromatosis 1 (NF-1), associated with pancreatic NETs. In the present review, we propose a reappraisal of the genetic basis and clinical features of gastroenteropancreatic and thoracic NETs in the setting of inherited syndromes with a special focus on molecularly targeted therapies for these lesions.

METHODS

Literature search was systematically performed through online databases, including MEDLINE (via PubMed), and Scopus using multiple keywords' combinations up to June 2022.

RESULTS

Somatostatin analogues (SSAs) remain the mainstay of systemic treatment for NETs, and radiolabelled SSAs can be used for peptide-receptor radionuclide therapy for somatostatin receptor (SSTR)-positive NETs. Apart of these SSTR-targeted therapies, other targeted agents have been approved for NETs: the mTOR inhibitor everolimus for lung, gastroenteropatic and unknown origin NET, and sunitinib, an antiangiogenic tyrosine kinase inhibitor, for pancreatic NET. Novel targeted therapies with other antiangiogenic agents and immunotherapies have been also under evaluation.

CONCLUSIONS

Major advances in the understanding of genetic and epigenetic mechanisms of NET development in the context of inherited endocrine disorders have led to the recognition of molecular targetable alterations, providing a rationale for the implementation of treatments and development of novel targeted therapies.

Biochemical factors in the blood serum of neuroendocrine tumor patients with carcinoid syndrome

Introduction. Carcinoid syndrome is the most common functional syndrome in patients with neuroendocrine tumors. More than 40 biochemical factors are responsible for the manifestation of carcinoid syndrome, among which serotonin is the most important. The study of biochemical markers of carcinoid syndrome and associated carcinoid heart disease is an important aim of laboratory examination in neuroendocrine tumors patients.Aim. Analysis of levels and diagnostic efficiency evaluation of chromogranin A (CgA), serotonin, pro-brain natriuretic peptide (proBNP) and platelet-derived growth factor (PDGF-BB) in the blood serum of neuroendocrine tumors patients with various clinical manifestations, including carcinoid syndrome and carcinoid heart disease.Materials and methods. 66 patients with neuroendocrine tumors of various localizations were examined (pancreas – 24 cases, small intestine – 21, large intestine – 6, lungs – 10, unkown primary focus – 5). 38 patients had liver metastases. In 43 patients, a clinic of carcinoid syndrome was observed, 16 had signs of carcinoid heart disease. The control group consisted of 30 practically healthy people. Serum levels of CgA, serotonin, and PDGF-BB were determined by enzyme immunoassay in microplate format: Chromogranin A NEOLISA (Eurodiagnostica, Sweden), Serotonin ELISA (IBL, German), and PDGF-BB ELISA Kit (Invitrogen, USA). The proBNP analysis was performed on a Cobas e601 automated analyzer (Roche, Switzerland).Results. In carcinoid syndrome, the medians of CgA, serotonin, and proBNP were the highest, differing statistically significantly from the control group. In patients with G3 tumors, the median PDGF-BB was statistically significantly higher than in controls, in contrast to G1 and G2. The highest diagnostic sensitivity in the general neuroendocrine tumors group was in CgA – 63.6 %, with a specificity of 100 %. In patients with carcinoid syndrome, the highest diagnostic sensitivity was characteristic of serotonin and chromogranin A (79 %), while in patients with CAD clinic, proBNP had the highest sensitivity – 93.8 %.Conclusion. The study revealed the high efficiency of СgA, with the highest sensitivity in common forms and tumors with high biological activity. Serotonin can be used in the diagnosis of carcinoid syndrome, associated with cardiofibrosis development. Pro-brain natriuretic peptide is a highly sensitive and specific marker of carcinoid heart disease. The highest levels of PDGF-BB are associated with a high grade of neuroendocrine tumors malignancy.

The anti-anxiety/depression effect of a combined complex of casein hydrolysate and γ-aminobutyric acid on C57BL/6 mice

In view of a series of adverse side effects of drugs for anxiety/depression on the market at present, it is imminent to extract and develop novel anti-anxiety and depression drugs from plants and proteins (like casein hydrolysate) as adjuncts or substitutes for existing anti-anxiety and depression drugs. Consequently, this study investigated the improvement of the anxiety/depression function by the compound of casein hydrolysate and γ-aminobutyric acid (GABA) (casein hydrolysate: GABA = 4:1; CCHAA) on mice induced by chronic restraint stress-corticosterone injection. Animal experiments revealed that oral gavage administration of CCHAA significantly reversed the anxiety/depression-like behaviors. Compared to the model control group, body weights were increased after treatment with CCHAA groups [1.5, 0.75 mg/(g⋅d)]. As a diagnostic index of anxiety and depression, we assessed GABA and 5-HT levels in response to CCHAA ingestion. The GABA and 5-HT levels were increasingly enhanced by the CCHAA diet. In addition, histopathological changes in the hippocampus CA3 region of the anxious/depressed mice were also alleviated after the treatment with the CCHAA. Thus, the casein hydrolysate and GABA formula diets may induce beneficial effects on the mice with anxiety/depression.

Sex differences in carcinoid syndrome: A gap to be closed

The incidence of neuroendocrine neoplasms and related carcinoid syndrome (CS) has markedly increased over the last decades and women seem to be more at risk than men for developing CS. Nevertheless, very few studies have investigated sex differences in clinical presentation and outcomes of CS. However, as per other tumours, sex might be relevant in influencing tumour localization, delay in diagnosis, clinical outcomes, prognosis and overall survival in CS. The present review was aimed at evaluating sex differences in CS, as they emerge from an extensive search of the recent literature. It emerged that CS occurs more frequently in female than in male patients with NENs and women seem to have a better prognosis and a slight advantage in overall survival and response to therapy. Moreover, the disease likely impacts differently the quality of life of men and women, with different psychological and social consequences. Nevertheless, sex differences, even if partially known, are deeply underestimated in clinical practice and data from clinical trials are lacking. There is urgent need to increase our understanding of the sex-related differences of CS, in order to define tailored strategies of management of the disease, improving both the quality of life and the prognosis of affected patients.

What Gastroenterologists Should Know about Carcinoid Syndrome

Carcinoid syndrome (CS) is the most common functional syndrome associated with neuroendocrine neoplasia (NEN), particularly in intestinal NEN with extensive liver metastases. Owing to the heterogenous symptomatic scenario present in CS, recognition of these patients may be challenging. In this review, we explore some key clinical factors used to identify patients affected by CS, with particular focus on differential diagnoses of diarrhea, which is the main symptom of CS. Moreover, we highlight the importance of nutritional screening as a clinical indication to prevent malnutrition and to manage the most common nutrient deficiencies present in these patients.

Bronchial Carcinoids: From Molecular Background to Treatment Approach

Simple Summary

Bronchial carcinoids (BCs) are uncommon and usually slow growing neuroendocrine epithelial malignancies that represent less than 2% of all lung cancers. Differences in the extent of molecular alterations between neuroendocrine carcinomas and BCs may underline the differences in the aggressiveness of these lesions. Moreover, although atypical BCs and typical BCs have similar set of mutations, some differential molecular and genetic alterations have been described between these two entities. A better understanding of the genetic and molecular background of BCs would allow a better selection of medical treatments in these patients. Regarding treatment, most BCs can be cured by surgery; however, inoperable tumors are mostly insensitive to chemotherapy and radiotherapy. In advanced BCs, the only drug that has a positive phase III clinical trial in BCs is everolimus. Somatostatin analogues constitute the gold standard for symptomatic relief. Peptide receptor radionuclide therapy has been associated with longer progression free. The efficacy of other treatments such as antiangiogenic agents and immunotherapy is still not established.

Abstract

A better understanding of the genetic and molecular background of bronchial carcinoids (BCs) would allow a better estimation of the risk of disease progression and the personalization of treatment in cases of advanced disease. Molecular studies confirmed that lungs neuroendocrine tumors (NETs) and neuroendocrine carcinomas (NECs) are different entities; thus, no progression of NET to NEC is expected. In BCs, MEN1 gene mutations and deletions and decreased gene expression have been associated with a poor prognosis. ATRX mutation has also been linked to a shorter disease-specific survival. In terms of therapeutic targets, PI3K/AKT/mTOR pathway mutations have been described in 13% of typical carcinoids (TCs) and 39% of atypical carcinoids (ACs), representing a targetable mutation with kinase inhibitors. Regarding treatment, surgical resection is usually curative in localized BCs and adjuvant treatment is not routinely recommended. Multiple options for systemic therapy exist for patients with advanced BCs, although limited by a heterogeneity in the scientific evidence behind their use recommendation. These options include somatostatin analogues, everolimus, peptide receptor radionuclide therapy, chemotherapy, radiotherapy, antiangiogenic agents, and immunotherapy. In this article, we provide a comprehensive review about the molecular and genetic background of BCs, and about the treatment of local and metastatic disease, as well as the main paraneoplastic syndromes that have been associated with this tumor.

Recent Advances in the Diagnosis and Management of Carcinoid Syndrome

Carcinoid syndrome, a paraneoplastic condition linked with the release of multiple humoral factors, affects around 30-40% of patients with well-differentiated neuroendocrine tumours. Carcinoid syndrome has a major and unfavourable impact on patients' quality of life; it raises costs when compared to non-functioning neuroendocrine tumours; and it causes patients' lifestyles to alter, such as food, job, physical activity, and social life. Somatostatin analogues have been the first-line therapy for individuals with neuroendocrine tumours and carcinoid disease for decades. While these drugs give considerable relief from carcinoid syndrome symptoms, clinical progression is unavoidable, necessitating further research into newer treatment measures. Carcinoid tumours are sometimes difficult to diagnose because of their vague or nonspecific symptoms. There have been several advancements in all aspects of carcinoid syndrome, as well as novel therapeutics, in the previous few years. New epidemiological studies show that it is becoming more common; increasing insights into the pathogenesis of its various clinical manifestations and its natural history: definition of prognostic factors; new methods to verify its presence; the development of new drugs to treat its various manifestations, both initially and in somatostatin-refractory cases; and an increased understanding of the pathogenesis, natural history, and management of the disease. An all language literature search was conducted on MEDLINE, COCHRANE, EMBASE, and Google Scholar till November 2021. The following search strings and Medical Subject Headings (MeSH) terms were used: "Recent advances", "Carcinoid syndrome", "Neuroendocrine Neoplasms" and "Carcinoid heart disease". We comprehensively reviewed the literature on the pathogenesis, clinical features, and newer treatment modalities for Carcinoid Syndrome. Recent advancements in research and management have resulted from advances in our understanding of the aetiology of carcinoid syndrome. The development of molecular indicators of aggressiveness improved serum tumour markers, and the molecular aetiology of carcinoid heart disease are all possible because of advances in molecular biology. We conducted a comprehensive review to update knowledge regarding the pathophysiology, diagnostic protocols, and current and newer treatments for carcinoid syndrome, which presently requires a multidisciplinary approach, due to the complexity of the illness's aetiology, diagnosis, and therapy.

Update in carcinoid heart disease - the heart of the matter

Carcinoid heart disease (CHD) is a paraneoplastic cardiac manifestation occurring in patients with carcinoid syndrome (CS) and advanced neuroendocrine malignancy. In about 20-40% of patients with CS, chronic exposure to tumor-released circulating vasoactive peptides typically results in right-sided valvular fibrosis leading to valve dysfunction and right heart failure. CHD remains a significant cause of morbidity and mortality. The management of patients with CHD is complex, as both the systemic malignant disease and the heart involvement have to be addressed. Early diagnosis and timely surgical intervention in selected patients are of utmost importance and offer a survival benefit. In patients with advanced carcinoid heart disease, valve replacement surgery is the most effective option to alleviate cardiac symptoms and contribute to survival outcomes. A collaboration of a multidisciplinary team in centers with experience is required to provide optimal patient management. Here, we review the current literature regarding CHD presentation, pathophysiology, diagnostic tools, and available treatment strategies.

Carcinoid Syndrome and Hyperinsulinemic Hypoglycemia Associated with Neuroendocrine Neoplasms: A Critical Review on Clinical and Pharmacological Management

The carcinoid syndrome (CS) and hyperinsulinemic hypoglycemia (HH) represent two of the most common clinical syndromes associated with neuroendocrine neoplasms (NENs). The former is mainly related to the serotonin secretion by a small bowel NEN, whereas the latter depends on an insulin hypersecretion by a pancreatic insulinoma. Both syndromes/conditions can affect prognosis and quality of life of patients with NENs. They are often diagnosed late when patients become strongly symptomatic. Therefore, their early detection and management are a critical step in the clinical management of NEN patients. A dedicated and experienced multidisciplinary team with appropriate therapeutic strategies is needed and should be encouraged to optimize clinical outcomes. This review aims to critically analyze clinical features, evidence and treatment options of CS and HH and therefore to improve their management.

Limited Diagnostic Utility of Chromogranin A Measurements in Workup of Neuroendocrine Tumors

BACKGROUND

Plasma chromogranin A (CgA) is related to tumor burden and recommended in the follow-up of patients diagnosed with neuroendocrine tumors (NETs). The use of CgA in the workup of a suspected NET is more questionable.

OBJECTIVE

To assess the positive predictive value (PPV) of CgA plasma concentrations above the upper reference limit (URL) in patients with suspected NET.

METHOD

Patients referred to the NET Centre, Rigshospitalet, Copenhagen from 2015 to 2019 with clinically suspected NET were included if a CgA measurement was performed prior to referral. The utility of CgA was assessed by comparing pre-referral CgA concentrations to the outcome of a thorough workup. In 47 selected cases with continuously unexplained elevated CgA concentrations, a processing-independent analysis (PIA) for CgA was performed.

RESULTS

A total of 197 patients were included. NET was ultimately diagnosed in 25 patients. CgA plasma concentrations were above the URL (elevated) in 19/25 patients diagnosed with NET. In total, 167/197 had elevated CgA concentrations at referral. The positive predictive value (PPV) of elevated CgA concentration was 11% (19/167). Proton pump inhibitor (PPI) treatment was identified as the possible cause of CgA elevation in 55/148 patients with falsely elevated CgA. CgA concentration was normal in 28/47 patients when using PIA.

CONCLUSION

Our data do not support using measurement of CgA for screening when NET is suspected since the PPV was rather low. PPI treatment is a common cause of increased CgA concentrations and should always be discontinued before CgA measurement. PIA of CgA could be a way of excluding NET when suspicion is based primarily on elevated CgA.

Bone Metabolism and Vitamin D Implication in Gastroenteropancreatic Neuroendocrine Tumors

Patients affected by gastroenteropancreatic–neuroendocrine tumors (GEP–NETs) have an increased risk of developing osteopenia and osteoporosis, as several factors impact on bone metabolism in these patients. In fact, besides the direct effect of bone metastasis, bone health can be affected by hormone hypersecretion (including serotonin, cortisol, and parathyroid hormone-related protein), specific microRNAs, nutritional status (which in turn could be affected by medical and surgical treatments), and vitamin D deficiency. In patients with multiple endocrine neoplasia type 1 (MEN1), a hereditary syndrome associated with NET occurrence, bone damage may carry other consequences. Osteoporosis may negatively impact on the quality of life of these patients and can increment the cost of medical care since these patients usually live with their disease for a long time. However, recommendations suggesting screening to assess bone health in GEP–NET patients are missing. The aim of this review is to critically analyze evidence on the mechanisms that could have a potential impact on bone health in patients affected by GEP–NET, focusing on vitamin D and its role in GEP–NET, as well as on factors associated with MEN1 that could have an impact on bone homeostasis.