Whole-body (11)C-5-hydroxytryptophan positron emission tomography as a universal imaging technique for neuroendocrine tumors: comparison with somatostatin receptor scintigraphy and computed tomography

Positron emission tomography ligand [11C]5-hydroxy-tryptophan can be used as a surrogate marker for the human endocrine pancreas

In humans, a well-developed serotonin system is localized to the pancreatic islets while being absent in exocrine pancreas. Assessment of pancreatic serotonin biosynthesis could therefore be used to estimate the human endocrine pancreas. Proof of concept was tested in a prospective clinical trial by comparisons of type 1 diabetic (T1D) patients, with extensive reduction of β-cells, with healthy volunteers (HVs). C-peptide-negative (i.e., insulin-deficient) T1D subjects (n = 10) and HVs (n = 9) underwent dynamic positron emission tomography with the radiolabeled serotonin precursor [(11)C]5-hydroxy-tryptophan ([(11)C]5-HTP). A significant accumulation of [(11)C]5-HTP was obtained in the pancreas of the HVs, with large interindividual variation. A substantial and highly significant reduction (66%) in the pancreatic uptake of [(11)C]5-HTP in T1D subjects was observed, and this was most evident in the corpus and caudal regions of the pancreas where β-cells normally are the major constituent of the islets. [(11)C]5-HTP retention in the pancreas was reduced in T1D compared with nondiabetic subjects. Accumulation of [(11)C]5-HTP in the pancreas of both HVs and subjects with T1D was in agreement with previously reported morphological observations on the β-cell volume, implying that [(11)C]5-HTP retention is a useful noninvasive surrogate marker for the human endocrine pancreas.

Neuroendocrine tumors of the gastrointestinal tract: Case reports and literature review

Neuroendocrine tumors (NET) previously called carcinoid tumors are neoplasms of enterochromaffin/neuroendocrine cell origin which display neurosecretory capacity that may result in the carcinoid syndrome. The annual incidence of patients with NET is 8.4 per 100000; yet many NET remain asymptomatic and clinically undetected. A majority of NET follows a benign course; however, some will display malignant characteristics. NET most commonly occur in the gastrointestinal tract (67%) and bronchopulmonary system (25%). Gastrointestinal NET occur within the stomach, small intestine, liver, and rectum. We report a retrospective study of 11 subjects: Eight with benign carcinoid tumors: duodenal bulb (n = 2), terminal ileum (n = 1), sigmoid colon (n = 2), and rectum (n = 3); three with malignant carcinoid: liver (n = 1) and intra-abdominal site (n = 2). The diagnosis, endoscopic images, outcome, treatment and review of the literature are presented.

(18)F-FDG PET/CT can be used to detect non-functioning pancreatic neuroendocrine tumors

18F-Fluorodeoxyglucose positron emission tomo-graphy and computed tomography (18F-FDG PET/CT) has limited value in well-differentiated neuroendocrine tumors. The value of 18F-FDG PET/CT in non-functioning pancreatic neuroendocrine tumors, which are often poorly differentiated, malignant, and present at an advanced stage, was also thought to be limited. This study was performed to evaluate the clinical value of 18F-FDG PET/CT in assessing non-functioning pancreatic neuroendocrine tumors. From January 2010 to February 2014, a comparable large cohort of patients (31 cases) with non-functioning pancreatic neuroendocrine tumors from Shanghai Cancer Center underwent 18F-FDG PET/CT scans. Demographics and clinical characteristics were retrospectively collected and analyzed for all the patients. Twenty-eight of 31 (90.3%) patients with non-functioning endocrine pancreatic tumors had an elevated 18F-FDG uptake (SUVmax ≥2.5). In addition, 18F-FDG PET/CT visualized 38 of 42 (90.5%) distant metastatic lesions. The 18F-FDG uptake had significant association with tumor size (P=0.012) and TNM stage (P=0.004). The application of 18F-FDG PET/CT has changed the management of 8 cases (8/31, 25.8%). In conclusion, 18F‑FDG PET/CT plays an important role in detecting and staging non-functioning pancreatic neuroendocrine tumors.

Detection of metastatic insulinoma by positron emission tomography with [(68)ga]exendin-4-a case report

CONTEXT

Insulinomas are the most common cause of endogenous hyperinsulinemic hypoglycemia in nondiabetic adult patients. They are usually benign, and curative surgery is the "gold standard" treatment if they can be localized. Malignant insulinomas are seen in less than 10% of patients, and their prognosis is poor. The glucagon like peptide-1 receptor (GLP-1R) is markedly up-regulated in insulinomas-especially benign lesions, which are difficult to localize with current imaging techniques.

OBJECTIVE

The aim of the study was to assess the possibility of the detection of primary and metastatic insulinoma by positron emission tomography (PET) using [(68)Ga]Ga-DO3A-VS-Cys(40)-Exendin-4 ([(68)Ga]Exendin-4) in a patient with severe hypoglycemia.

DESIGN AND SETTING

Dynamic and static PET/computed tomography (CT) examination of a patient was performed using [(68)Ga]Exendin-4 at Uppsala University Hospital, Uppsala, Sweden.

PATIENTS

A patient presented with hypoglycemia requiring continuous iv glucose infusions. A pancreatic insulinoma was suspected, and an exploratory laparotomy was urgently performed. At surgery, a tumor in the pancreatic tail with an adjacent metastasis was found, and a distal pancreatic resection (plus splenectomy) and removal of lymph node were performed. Histopathology showed a World Health Organization classification grade II insulinoma. Postoperatively, hypoglycemia persisted, but a PET/CT examination using the neuroendocrine marker [(11)C]-5-hydroxy-L-tryptophan was negative.

INTERVENTIONS

The patient was administered [(68)Ga]Exendin-4 and was examined by dynamic PET over the liver and pancreas.

RESULTS

The stable GLP-1 analog Exendin-4 was labeled with (68)Ga for PET imaging of GLP-1R-expressing tumors. The patient was examined by [(68)Ga]Exendin-4-PET/CT, which confirmed several small GLP-1R-positive lesions in the liver and a lymph node that could not be conclusively identified by other imaging techniques. The results obtained from the [(68)Ga]Exendin-4-PET/CT examination provided the basis for continued systemic treatment.

CONCLUSION

The results of the [(68)Ga]Exendin-4-PET/CT examination governed the treatment strategy of this particular patient and demonstrated the potential of this technique for future management of patients with this rare but potentially fatal disease.

GEP-NETS update: functional localisation and scintigraphy in neuroendocrine tumours of the gastrointestinal tract and pancreas (GEP-NETs)

For patients with neuroendocrine tumours (NETs) of the gastrointestinal tract and pancreas (GEP) (GEP-NETs), excellent care should ideally be provided by a multidisciplinary team of skilled health care professionals. In these patients, a combination of nuclear medicine imaging and conventional radiological imaging techniques is usually mandatory for primary tumour visualisation, tumour staging and evaluation of treatment. In specific cases, as in patients with occult insulinomas, sampling procedures can provide a clue as to where to localise the insulin-hypersecreting pancreatic NETs. Recent developments in these fields have led to an increase in the detection rate of primary GEP-NETs and their metastatic deposits. Radiopharmaceuticals targeted at specific tumour cell properties and processes can be used to provide sensitive and specific whole-body imaging. Functional imaging also allows for patient selection for receptor-based therapies and prediction of the efficacy of such therapies. Positron emission tomography/computed tomography (CT) and single-photon emission CT/CT are used to map functional images with anatomical localisations. As a result, tumour imaging and tumour follow-up strategies can be optimised for every individual GEP-NET patient. In some cases, functional imaging might give indications with regard to future tumour behaviour and prognosis.

Quantitative imaging of serotonergic biosynthesis and degradation in the endocrine pancreas

Serotonergic biosynthesis in the endocrine pancreas, of which the islets of Langerhans is the major constituent, has been implicated in insulin release and β cell proliferation. In this study, we investigated the feasibility of quantitative noninvasive imaging of the serotonergic metabolism in the pancreas using the PET tracer (11)C-5-hydroxy-l-tryptophan ((11)C-5-HTP).

METHODS

Uptake of (11)C-5-HTP, and its specificity for key enzymes in the serotonergic metabolic pathway, was assessed in vitro (INS-1 and PANC1 cells and human islet and exocrine preparations) and in vivo (nonhuman primates and healthy and diabetic rats).

RESULTS

In vitro tracer uptake in endocrine cells (INS-1 and human islets), but not PANC1 and exocrine cells, was mediated specifically by intracellular conversion into serotonin. Pancreatic uptake of (11)C-5-HTP in nonhuman primates was markedly decreased by inhibition of the enzyme dopa decarboxylase, which converts (11)C-5-HTP to (11)C-serotonin and increased after inhibition of monoamine oxidase-A, the main enzyme responsible for serotonin degradation. Uptake in the rat pancreas was similarly modulated by inhibition of monoamine oxidase-A and was reduced in animals with induced diabetes.

CONCLUSION

The PET tracer (11)C-5-HTP can be used for quantitative imaging of the serotonergic system in the endocrine pancreas.

Neuroendocrine tumours: the role of imaging for diagnosis and therapy

In patients with neuroendocrine tumours (NETs), a combination of morphological imaging and nuclear medicine techniques is mandatory for primary tumour visualization, staging and evaluation of somatostatin receptor status. CT and MRI are well-suited for discerning small lesions that might escape detection by single photon emission tomography (SPECT) or PET, as well as for assessing the local invasiveness of the tumour or the response to therapy. Somatostatin receptor imaging, by (111)In-pentetreotide scintigraphy or PET with (68)Ga-labelled somatostatin analogues, frequently identifies additional lesions that are not visible on CT or MRI scans. Currently, somatostatin receptor scintigraphy with (111)In-pentetreotide is the more frequently available of the two techniques to determine somatostatin receptor expression and is needed to select patients for peptide receptor radionuclide therapy. In the future, because of its higher sensitivity, PET with (68)Ga-labelled somatostatin analogues is expected to replace somatostatin receptor scintigraphy. Whereas (18)F-FDG-PET is only used in high-grade neuroendocrine cancers, PET-CT with (18)F-dihydroxy-L-phenylalanine or (11)C-5-hydroxy-L-tryptophan is a useful problem-solving tool and could be considered for the evaluation of therapy response in the future. This article reviews the role of imaging for the diagnosis and management of intestinal and pancreatic NETs. Response evaluation and controversies in NET imaging will also be discussed.

Imaging features of carcinoid tumors of the gastrointestinal tract

OBJECTIVE

Recent studies have provided a better understanding of the biologic behavior of gastrointestinal carcinoid tumors. This article focusing on imaging of gastrointestinal carcinoids will emphasize epidemiology, molecular biology, taxonomy, histopathology, and management.

CONCLUSION

Gastrointestinal carcinoids are a biologically heterogeneous group of tumors, with variable clinical presentation and biologic behavior. Imaging can play an important role in multidisciplinary identification and management of this disease.

Other PET tracers for neuroendocrine tumors

In this article the applicability of (124)I-MIBG and (11)C-5-HTP PET for the detection of abdominal gastro-enteropancreatic neuroendocrine tumors is discussed. (124)I-MIBG is a positron-emitting variant of (123)I-MIBG and therefore suited for PET imaging. Due to the better intrinsic characteristics of PET, (124)I-MIBG PET has a higher spatial resolution than (123)I-MIBG and may therefore lead to better lesion detection in patients with neuroblastoma and pheochromocytoma. Research is ongoing to develop (18)F-labeled analogues and to assess its place in staging patients with gastro-enteropancreatic neuroendocrine tumors when compared with (18)F-FDOPA and (68)Ga-somatostatin PET analogues.

Somatostatin receptor-based molecular imaging and therapy for neuroendocrine tumors

Neuroendocrine tumors (NETs) are tumors originated from neuroendocrine cells in the body. The localization and the detection of the extent of NETs are important for diagnosis and treatment, which should be individualized according to the tumor type, burden, and symptoms. Molecular imaging of NETs with high sensitivity and specificity is achieved by nuclear medicine method using single photon-emitting and positron-emitting radiopharmaceuticals. Somatostatin receptor imaging (SRI) using SPECT or PET as a whole-body imaging technique has become a crucial part of the management of NETs. The radiotherapy with somatostatin analogues labeled with therapeutic beta emitters, such as lutetium-177 or yttrium-90, has been proved to be an option of therapy for patients with unresectable and metastasized NETs. Molecular imaging can deliver an important message to improve the outcome for patients with NETs by earlier diagnosis, better choice of the therapeutic method, and evaluation of the therapeutic response.

Pancreatic neuroendocrine neoplasms: diagnosis and management

Pancreatic neuroendocrine neoplasms are uncommon but rising in incidence. There have been recent changes in the WHO nomenclature and a newly proposed American Joint Committee on Cancer TNM staging, which complement each other. These neoplasms are of great medical and radiological interest because of their diverse presenting features and imaging appearances. There is an increased role for both anatomic and functional imaging in the assessment of these neoplasms. A review of the nomenclature, staging, and imaging is presented in this paper.

Primary carcinoid tumor of the cavernous sinus

BACKGROUND

Intracranial carcinoid tumors belong to the class of neuroendocrine tumors and their incidence is extremely rare. The pathogenesis and clinical manifestations of carcinoid tumors of the skull base are outlined in this case report.

CASE DESCRIPTION

A 61-year-old multimorbid woman presented with transient memory loss. Computed tomographic and magnetic resonance imaging scan of the brain demonstrated a left cavernous sinus mass extending into the infratemporal fossa. The lesion was biopsied using the Caldwell-Luc approach, and histology showed a low-grade neuroendocrine tumor. The tumor was subtotally resected with a neurosurgery/head and neck combined preauricular infratemporal and subtemporal extradural approaches to the cavernous sinus. Further histologic evaluation revealed that the tumor was of carcinoid differentiation with no other primary or metastatic sites detectable.

CONCLUSION

Primary intracranial carcinoid tumors, though rare, should be included in the differential diagnosis of extradural and dural-based lesions.

Role of PET/CT in the functional imaging of endocrine pancreatic tumors

Endocrine pancreatic tumors (EPTs) are a heterogeneous group of neoplasms with variable clinical and biological features and prognosis, ranging from very slow-growing tumors to highly aggressive and very malignant ones. As other neuroendocrine tumors, EPTs are characterized by the presence of neuroamine uptake mechanisms and/or peptide receptors at the cell membrane and these features constitute the basis of the clinical use of specific radiolabeled ligands, both for imaging and therapy. The more widespread use of hybrid machines, i.e., positron emission tomography/computed tomography (PET/CT), allows to perform imaging with high resolution and high diagnostic accuracy especially for small lesions, and to correlate anatomic location with function. The recent WHO recommendations for classification and prognostic factors help the selection of tracers likely to show a positive image on PET; therefore, tracers exploiting specific metabolic patterns ((18)F-DOPA and (11)C-5-HTP) or specific receptor expression ((68)Ga-DOTA-peptides) are suited to well-differentiated tumors, while the use of (18)F-FDG is preferred for poorly-differentiated neoplasms with high proliferative activity and loss of neuroendocrine features. In differentiated EPTs, (11)C-5-HTP performs better than (18)F-DOPA even though its use is hampered by its complex production and limited availability and experience; (68)Ga-peptides are indicated for all type of gastroenteropancreatic (GEP) neuroendocrine tumors, regardless of their functional activity. In addition, (68)Ga-DOTA-peptides play a distinctive role in planning peptide receptor radionuclide therapy.

Atypical or typical adrenocorticotropic hormone-producing pulmonary carcinoids and the usefulness of 11C-5-hydroxytryptophan positron emission tomography: two case reports

Introduction

Pulmonary carcinoids associated with ectopic adrenocorticotropic hormone secretion have a good prognosis if histological examination shows typical pulmonary carcinoid and low proliferation, whereas a poor outcome is linked to atypical pulmonary carcinoid and high proliferation. Here we describe the diagnostic challenges to find the tumor in Cushing’s syndrome secondary to ectopic adrenocorticotropic hormone secretion in two cases with an atypical and a typical pulmonary carcinoid, respectively.

Case presentation

A 63-year-old Caucasian woman presented with aggressive clinical features related to Cushing’s syndrome, having very high levels of urinary cortisol and circulating adrenocorticotropic hormone and cortisol. Magnetic resonance imaging showed no pituitary tumor, and bilateral inferior petrosal sinus sampling revealed no central peripheral ratio of adrenocorticotropic hormone. Computed tomography and ¹¹¹Indium-pentetreoide somatostatin receptor scintigraphy could not visualize any ectopic tumor. The patient was referred for an ¹¹C-5-hydroxytryptophan positron emission tomography, and a small 8mm nodule in her left lung was found. The tumor was removed via a lateral thoracic incision and wedge excision. The histological examination showed an atypical carcinoid with Ki-67 index of 9 to 10%, and an additional lobectomy was performed.

The second patient, a 22-year-old Caucasian man, also presented with aggressive Cushing’s syndrome, with very high urinary cortisol levels and increased circulating cortisol as well as adrenocorticotropic hormone levels. A magnetic resonance imaging scan of the pituitary showed no tumor, whereas a 12×9×14mm tumor was detected in the right lung on the primary computed tomography scan and no further investigation was performed. The tumor was removed via a lateral thoracic incision and wedge excision. A typical carcinoid with Ki-67 index of 1 to 2% was found and no further surgery was performed.

After surgical removal, the biochemical disturbances resolved and significant clinical improvement were achieved in both patients after 24 months of follow up.

Conclusions

Diagnostic evaluation time is limited due to the aggressive course in ectopic adrenocorticotropic hormone-dependent Cushing’s syndrome. We suggest that ¹¹C-5-hydroxytryptophan positron emission tomography could be considered early as a secondary diagnostic tool when primary computed tomography and/or magnetic resonance imaging scans fail to show any tumor.

Thymic neuroendocrine tumour in multiple endocrine neoplasia type 1: female patients are not rare exceptions

OBJECTIVE

Thymic neuroendocrine tumour (Th-NET) occurs in 2-5% of patients with MEN1 and has high malignant potency accompanying recurrence and distant metastasis. While Th-NET is recognized to develop predominantly in men and heavy smokers, a number of female patients have been reported in the literature. The objective of this study is to clarify the clinical features of MEN1 patients with Th-NET using database analysis.

DESIGN/PATIENTS

Clinical data of patients with Th-NET were extracted and analysed from a recently constructed database of Japanese MEN1 patients.

RESULTS

Among 560 registered cases, Th-NET was seen in 28 (5·0%) patients. Of note, 36% of patients (10/28) were women; only one patient among those was a smoker and another six patients were non-smokers. Age at diagnosis of Th-NET and MEN1, tumour size, prevalence of other MEN1-related tumours did not differ between male and female patients, and 10-year survival probability was 0·271 ± 0·106.

CONCLUSIONS

Although the prevalence of Th-NET in women (3·2%) is significantly lower than that in men (7·6%), a considerable proportion of female patients develop Th-NET. Given that Th-NET is a major determinant of life expectancy of patients, our results alert clinicians who treat patients with MEN1 that surveillance of Th-NET is essential even for female patients without a smoking habit.

The value of preoperative imaging in small bowel neuroendocrine tumors

BACKGROUND

Neuroendocrine tumors of the small bowel (SBNETs) are a rare but important subgroup of malignancies. Since 30 % of SBNETs present with metastatic disease, often with an occult primary, preoperative imaging is critical for determining who will benefit most from abdominal exploration. We set out to evaluate the usefulness of the two most commonly performed imaging modalities in predicting the extent of disease found at exploration in patients with SBNETs.

METHODS

A retrospective chart review was performed on patients with SBNETs resected at 1 institution. Data from preoperative computed tomography (CT) scans were reviewed to determine whether the primary tumor, nodal, or liver metastases were seen, then compared with intraoperative findings. Results of preoperative somatostatin receptor scintigraphy (SRS) were similarly examined.

RESULTS

A total of 62 patients with SBNETs were included. Of these patients, 42 of 62 (68 %) had distant metastases and 48 of 62 (77 %) had nodal metastases at exploration. A total of 56 patients had preoperative CT scans and 47 had SRS. Using CT, a primary tumor was localized to the small bowel in 27 of 56 (48 %) and nodal metastases seen in 33 of 56 (79 %) of cases. SRS found intra-abdominal uptake in 35 of 47 cases (74 %).

CONCLUSIONS

CT and SRS are complementary in making the diagnosis of SBNET, with CT giving more precise anatomical detail, while SRS helps to confirm that lesions are NETs and is useful for identifying occult extrahepatic sites of metastatic disease. However, 10-15 % of SBNETs were not identified by either test preoperatively, and therefore surgical exploration still plays an important role in making the diagnosis in these patients.

Improving the diagnosis and management of neuroendocrine tumors: utilizing new advances in biomarker and molecular imaging science

Neuroendocrine tumors (NET) are malignant solid tumors that arise in hormone-secreting tissue of the diffuse neuroendocrine system or endocrine glands. Although traditionally understood to be a rare disease, the incidence and prevalence of NET have increased greatly in the past 3 decades. However, during this time, progress in diagnosis and outcome of NET has generally been modest. In order to achieve improved outcome in NET, a better understanding of NET biology combined with more reliable serum markers and better techniques to identify tumor localization and small lesions are needed. Although some NET biomarkers exist, sensitive and specific markers that predict tumor growth and behavior are generally lacking. In addition, the integration of new molecular imaging technologies in patient diagnosis and follow-up has the potential to enhance care. To discuss developments and issues required to improve diagnostics and management of NET patients, with specific focus on the latest advances in molecular imaging and biomarker science, 17 global leaders in the fields of NET, molecular imaging and biomarker technology gathered to participate in a 2-day meeting hosted by Prof. Kjell Öberg at the University of Uppsala in Sweden. During this time, findings were presented regarding methods with potential prognostic and treatment applications in NET or other types of cancers. This paper describes the symposium presentations and resulting discussions.

Radiological and nuclear medicine imaging of gastroenteropancreatic neuroendocrine tumours

Neuroendocrine tumours (NETs) comprise a heterogeneous group of neoplasms with very varying clinical expression. A functioning NET, for instance in the pancreas, may be very small and yet give rise to severe endocrine symptoms whereas a patient with a small bowel tumour may present with diffuse symptoms and disseminated disease with a palpable bulky liver. Imaging of NETs is therefore challenging and the imaging needs in the various patients are diverse. The basic modalities for NET imaging are computed tomography (CT) or magnetic resonance imaging (MRI) in combination with somatostatin receptor imaging (SMI) by scintigraphy with 111In-labelled octreotide (OctreoScan) or more recently by positron emission tomography (PET) with 68Ga-labelled somatostatin analogues. In this review these various morphological and functional imaging modalities and important methodological aspects are described. Imaging requirements for the various types of NETs are discussed and typical image findings are illustrated.

Gastric neuroendocrine tumours

BACKGROUND

Gastric neuroendocrine tumours (NETs) are increasingly recognised, and management decisions may be difficult due to an incomplete understanding of aetiology, natural history and optimum therapy. This article presents a current understanding based on recent advances in epidemiology, classification, molecular profiling, and treatment.

METHODS

Relevant medical literature was identified from searches of PubMed and references cited in appropriate articles identified. Selection of articles was based on peer review, journal and relevance.

RESULTS

Gastric NETs may be divided into three clinical prognostic groups: type I is associated with autoimmune atrophic gastritis and hypergastrinaemia, type II is associated with Zollinger-Ellison syndrome, and type III lesions are gastrin-independent, have the greatest metastatic potential and poorest prognosis. There has been an increased frequency of gastric NETs reported. Management approaches have evolved in parallel with advances in endoscopic staging and surgery, as well as improved understanding of the biology and natural history of NETs.

CONCLUSIONS

Gastric NETs present a spectrum of activity from indolent tumours to metastatic malignancy. Treatment decisions for patients must be individualised and are best managed by a multidisciplinary team approach. The current evidence base is limited to small series and efforts to treat patients within clinical networks of expertise are warranted.

Nuclear medicine imaging of gastro-entero-pancreatic neuroendocrine tumors. The key role of cellular differentiation and tumor grade: from theory to clinical practice

Nuclear medicine imaging is a powerful diagnostic tool for the management of patients with gastro-entero-pancreatic neuroendocrine tumors, mainly developed considering some cellular characteristics that are specific to the neuroendocrine phenotype. Hence, overexpression of specific trans membrane receptors as well as the cellular ability to take up, accumulate, and decarboxylate amine precursors have been considered for diagnostic radiotracer development. Moreover, the glycolytic metabolism, which is not a specific energetic pathway of neuroendocrine tumors, has been proposed for radionuclide imaging of neuroendocrine tumors. The results of scintigraphic examinations reflect the pathologic features and tumor metabolic properties, allowing the in vivo characterization of the disease. In this article, the influence of both cellular differentiation and tumor grade in the scintigraphic pattern is reviewed according to the literature data. The relationship between nuclear imaging results and prognosis is also discussed. Despite the existence of a relationship between the results of scintigraphic imaging and cellular differentiation, tumor grade and patient outcome, the mechanism explaining the variability of the results needs further investigation.

How Does the Patient Benefit from Clinical PET?

Clinical molecular imaging by use of PET and PET/CT is increasingly important in routine oncological practice worldwide. A vast majority of clinical PET investigations are performed with [¹⁸F]-fluorodeoxyglucose (FDG), but there is a growing interest in novel molecular probes among scientists and clinicians. Beyond FDG, a small number of different tracers have been shown to be of clinical value. With a growing commercial interest in tracer development, many more are under investigation. This review provides some examples of clinical situations where tracers other than FDG have been found useful and an outlook towards technical and regulatory development needed to allow the full impact of clinical PET to benefit the individual patient.

Development and experimental medicine applications of PET in oncology: a historical perspective

Nearly 90 years of scientific research have led to the use of PET and the ability to forge advances in the field of oncology. In this Historial Review we outline the key developments made with this imaging technique, including the evolution of cyclotrons and scanners, together with the associated advances made in image reconstruction, presentation, analysis of data, and radiochemistry. The applications of PET to experimental medicine are summarised, and we cover how these are related to the use and development of PET, especially in the assessment of tumour biology and pharmacology. The use of PET in clinical oncology and for tissue pharmacokinetic and pharmacodynamic studies as a means of supporting drug development is detailed. The current limitations of the technology are also discussed.

11C-5-hydroxytryptophan positron emission tomography after radiofrequency ablation of neuroendocrine tumor liver metastases

AIM

The aim was to assess the feasibility of (11)C-5-hydroxy-tryptophan positron emission tomography ((11)C-5-HTP-PET) in the follow-up after radiofrequency ablation (RFA) of liver metastases from neuroendocrine tumors (NETs).

BACKGROUND

Contrast-enhanced computed tomography (CECT) and contrast-enhanced ultrasound (CEUS) are commonly used to evaluate the liver after RFA of NETs. In general, (11)C-5-HTP-PET is more sensitive in the visualization of NETs, but no studies have investigated its role after RFA.

METHODS

Six consecutive patients with liver metastases from NETs were subjected to RFA treatment. All patients underwent baseline imaging before RFA and on two occasions (1-2 and 6-11 months) after RFA. The imaging consisted of (11)C-5-HTP-PET, CEUS and CECT on all three occasions.

RESULTS

Thirty RFA areas were evaluated, and residual tumors (RTs) were depicted in eight areas (22%). (11)C-5-HTP-PET depicted RTs after RFA with maximum sensitivity (100%) and specificity (100%), using radiological follow-up as the gold standard. (11)C-5-HTP-PET detected five out of eight RTs earlier than CECT or CEUS. In general, the sensitivity of (11)C-5-HTP-PET exceeded that of CECT and CEUS for early visualization of NET liver metastases.

CONCLUSION

(11)C-5-HTP-PET can be used in the follow-up after RFA for the purpose of detecting RT, and it provides additional information to CEUS and CECT by detecting new lesions.

New strategies for advanced neuroendocrine tumors in the era of targeted therapy

Low- to intermediate-grade neuroendocrine tumor (NET) constitutes a group of indolent malignancies that share the capacity for secreting hormones and neuroamines. Until recently, there were few therapeutic options for oncologic control. The PROMID study showed that octreotide long-acting repeatable formulation can delay tumor growth in midgut NETs. And, recent phase III studies showed both everolimus and sunitinib improved progression-free survival in pancreatic NETs, validating the phosphoinositide 3-kinase/Akt/mTOR pathway and angiogenesis as important targets for further advances. Ongoing and planned pivotal studies targeting these pathways in other NET subtypes may widen their therapeutic application. Development of rational combinations may further improve therapeutic outcome. These successes and our improved understanding of the underlying molecular biology are likely to lead to further important advances on the horizon.

PET-Guided Surgery - High Correlation between Positron Emission Tomography with 11C-5-Hydroxytryptophane (5-HTP) and Surgical Findings in Abdominal Neuroendocrine Tumours

Positron emission tomography (PET) with 11C-labeled 5-hydroxytryptophane (5-HTP) is a sensitive technique to visualize neuroendocrine tumours (NETs), due to high intracellular uptake of amine-precursors like L-dihydroxyphenylalanine (L-DOPA) and 5-HTP. NETs are often small and difficult to localize in spite of overt clinical symptoms due to hormonal excess. In our study, 38 consecutive NET patients underwent 11C-5-HTP-PET and morphological imaging by CT within 12 weeks prior to surgery. Surgical, histopathological and 5-HTP PET findings were correlated. 11C-5-HTP-PET corresponded to the surgical findings in 31 cases, was false negative in six, and true negative in one case resulting in 83.8% sensitivity and 100% specificity. Positive predicted value was 100%. In 11 patients 11C-5-HTP-PET was the only imaging method applied to localize the tumour. Thus, we could demonstrate that functional imaging by 11C-5-HTP-PET in many cases adds vital preoperative diagnostic information and in more than every fourth patient was the only imaging method that will guide the surgeon in finding the NET-lesion. Although the present results demonstrates that 11C-5-HTP may be used as an universal NET tracer, the sensitivity to visualize benign insulinomas and non functioning pancreatic NETs was lower.

Diagnostic work-up of gastroenteropancreatic neuroendocrine tumors

Neuroendocrine tumors are a heterogeneous group of malignancies that present a diagnostic challenge. The majority of patients (more than 60%) present with metastatic disease at diagnosis. The diagnosis is based on histopathology, imaging, and circulating biomarkers. The histopathology should contain specific neuroendocrine markers such as chromogranin A, synaptophysin, and neuron-specific enolase and also an estimate of the proliferation by Ki-67 (MIB1). Standard imaging procedures consist of computed tomography or magnetic resonance imaging together with somatostatin receptor scintigraphy. 68Ga-DOTA-octreotate scans will in the future replace somatostatin receptor scintigraphy because they have higher specificity and sensitivity. Other positron imaging tomographic scanning tracers that will come into clinical use are 18F-DOPA and 11C-5HTP. Neuroendocrine tumors secrete many different peptides and amines that can be used as circulating biomarkers. The most useful general marker is chromogranin A, which is both a diagnostic and prognostic marker in most neuroendocrine tumors. However, there is still a need for improved biomarkers for early detection and follow-up of patients during treatment. In addition, molecular imaging can be further developed for both detection and evaluation of treatment.

Surgical management of pancreatico-duodenal tumors in multiple endocrine neoplasia syndrome type 1

Pancreatico-duodenal tumors are the second most common endocrinopathy in multiple endocrine neoplasia syndrome type 1, and have a pronounced effect on life expectancy as the principal cause of disease-related death. Previous discussions about surgical management have focused mainly on syndromes of hormone excess and, in particular, the management of multiple endocrine neoplasia syndrome type 1-related Zollinger-Ellison syndrome. Since hormonal syndromes tend to occur late and indicate the presence of metastases, screening with biochemical markers and endoscopic ultrasound is recommended for early detection of pancreatico-duodenal tumors, and with early surgery before metastases have developed. Surgery is recommended in patients with or without hormonal syndromes in the absence of disseminated liver metastases. The suggested operation includes distal 80% subtotal pancreatic resection together with enucleation of tumors in the head of the pancreas, and in cases with Zollinger-Ellison syndrome, excision of duodenal gastrinomas together with clearance of regional lymph node metastases. This strategy, with early and aggressive surgery before metastases have developed, is believed to reduce the risks for tumor recurrence and malignant progression.

Primary Hepatic Neuroendocrine Tumor: What Do We Know Now?

Primary hepatic neuroendocrine tumors (PHNETs) are rear neoplasm. Diagnosis is an evolution, and requires a systematic clinical exclusion with histological confirmation. Treatment is surgical with excellent prognosis, and a long-term follow-up is required due to high tumor recurring rate. Knowledge from this species of tumor remains limited due to paucity of cases. This article elaborates the key features, diagnosis algorithm, current management, other treatment options and extensive review of literature on this rear tumor.

Nuclear medicine techniques for the imaging and treatment of neuroendocrine tumours

Nuclear medicine plays a pivotal role in the imaging and treatment of neuroendocrine tumours (NETs). Somatostatin receptor scintigraphy (SRS) with [(111)In-DTPA(0)]octreotide has proven its role in the diagnosis and staging of gastroenteropancreatic NETs (GEP-NETs). New techniques in somatostatin receptor imaging include the use of different radiolabelled somatostatin analogues with higher affinity and different affinity profiles to the somatostatin receptor subtypes. Most of these analogues can also be labelled with positron-emitting radionuclides that are being used in positron emission tomography imaging. The latter imaging modality, especially in the combination with computed tomography, is of interest because of encouraging results in terms of improved imaging quality and detection capabilities. Considerable advances have been made in the imaging of NETs, but to find the ideal imaging method with increased sensitivity and better topographic localisation of the primary and metastatic disease remains the ultimate goal of research. This review provides an overview of the currently used imaging modalities and ongoing developments in the imaging of NETs, with the emphasis on nuclear medicine and puts them in perspective of clinical practice. The advantage of SRS over other imaging modalities in GEP-NETs is that it can be used to select patients with sufficient uptake for treatment with radiolabelled somatostatin analogues. Peptide receptor radionuclide therapy (PRRT) is a promising new tool in the management of patients with inoperable or metastasised NETs as it can induce symptomatic improvement with all Indium-111, Yttrium-90 or Lutetium-177-labelled somatostatin analogues. The results that were obtained with [(90)Y-DOTA(0),Tyr(3)]octreotide and [(177)Lu-DOTA(0),Tyr(3)]octreotate are even more encouraging in terms of objective tumour responses with tumour regression and documented prolonged time to progression. In the largest group of patients receiving PRRT, treated with [(177)Lu-DOTA(0),Tyr(3)]octreotate, a survival benefit of several years compared with historical controls has been reported.

[Diagnosis and therapy of bronchopulmonary carcinoid tumors]

支气管肺类癌是罕见的肺部肿瘤，总体生长缓慢、预后尚可。根据其临床特征往往可以推测支气管肺类癌的诊断和亚型并指导治疗。其中年轻、CT表现为中心型肿瘤且无肺门或纵隔淋巴结肿大的病例，典型类癌的可能性较大。此亚型远处转移几率小，在手术治疗前除胸增强CT外可以不进行其它的常规术前分期检查。中心型肿瘤临床怀疑纵隔淋巴结累及或周围型肿瘤临床怀疑肺门纵隔淋巴结累及的病例，可能为不典型类癌。此亚型应做全面术前评估和分期。累及纵隔淋巴结的不典型类癌预后相对较差，应行多学科积极治疗。支气管肺类癌虽然其生物学特性不活跃，但均为恶性肿瘤，放化疗效果差，手术切除是最主要的治疗手段。彻底切除肿瘤、最大限度保留正常的肺组织是此类肺肿瘤外科治疗的基本目标。

Tailored imaging of islet cell tumors of the pancreas amidst increasing options

Pancreatic islet cell tumors are neuroendocrine tumors, which can produce hormones and can arise as part of multiple endocrine neoplasia type 1 or von-Hippel-Lindau-disease, two genetically well-defined hereditary cancer syndromes. Currently, technical innovation improves conventional and specific molecular imaging techniques. To organize the heterogeneous results described for the imaging of these tumors, we distinguished three indications (1) imaging of a patient with hormone hypersecretion, (2) search for a pancreatic primary in case of proven neuroendocrine cancer of unknown primary, and (3) screening of asymptomatic mutation carriers. We searched for publications on imaging of islet cell tumors between 1995 and January 2010 and defined a Level of Evidence (LOE) for the applicability of each technique. For each technique, data were analyzed in a Forest plot and arranged per imaging indication and tumor subtype. LOEs are weak for all imaging techniques. Analyses indicate a prominent role for endoscopic ultrasound for all three indications.

Current knowledge on diagnosis and staging of neuroendocrine tumors

Neuroendocrine tumors (NETs) consist of a heterogeneous group of malignancies with various clinical presentations and growth rates. The incidence has been estimated to 2.5-5 per 100,000 people per year and prevalence of 35 per 100,000. The largest group is the gastroenteropancreatic NETs. Small intestinal NETs are the most common followed by pancreatic NETs in the gastrointestinal tract. A classification system (World Health Organization) was established in year 2000 and recently updated in 2010, taking into consideration the histopathology and tumor biology of the tumors. To further refine the classification a "tumor node metastasis" staging has been suggested by the European Neuroendocrine Tumor Society. The same organization has also proposed a grading system (G1, G2, and G3). The diagnosis of a NET is based on histopathology on tumor specimens, circulating biomarkers as well as imaging. Traditional radiology, such as computerized tomography and magnetic resonance imaging, is still the basis but is complemented with somatostatin receptor scintigraphy and positron emission tomography with specific isotopes such (68)Ga-DOTA-octreotate, F18-dopamine, or C11-5 hydroxytryptamine. Molecular imaging will increase in importance in the near future. There is still an unmet need for more sensitive biomarkers for diagnosis and follow-up.

Future perspectives on neuroendocrine tumors

In the last 30 years the incidence and prevalence of gastroenteropancreatic neuroendocrine tumors (GEP-NETs) has increased substantially. This could be partly due to improvements in diagnostic imaging, which lead to the incidental diagnosis of asymptomatic cases. However, despite these improvements, patients typically experience long delays before they are diagnosed. In this review, we discuss both the limitations and advances in our understanding of the pathogenesis, molecular and cellular biology, diagnosis, classification, staging, and treatment of GEP-NETs in order to identify which factors could be contributing to the delay in diagnosis and timely treatment of these patients. Within this context, the results from the most relevant clinical trials the available targeted therapies for the treatment of GEP-NETs, such as the "RAD001 in Advanced Neuroendocrine Tumors," will be discussed.

[Somatostatin receptor-based imaging and therapy of digestive endocrine tumors]

The management of gastroenteropancreatic endocrine tumors is greatly linked to the localization of primary tumor. Morphological imaging methods are thus necessary. However, the expression of somatostatin receptors in endocrine tumors makes their detection possible thanks to radiolabeled somastotatin analogs. [(111)In-DTPA] octreotide is the main radiolabeled analog for somatostatin receptor scintigraphy. Positron emission tomography uses other tracers and currently allows improvement of the diagnosis and the tumoral staging. It also allows to affect the therapeutic management. A further step is about to be taken as far as the therapy of endocrine tumors is concerned with the peptide receptor radionuclide therapy. Those therapies are now being offered in some European and American centers for progressive metastatic tumors. Their place in the therapeutic strategy has to be defined, especially in comparison to targeted therapy. The sudden and delayed adverse events as well as the current legislation on the use of radioactive therapy-aimed products have limited their development in France so far.

New and emerging syndromes due to neuroendocrine tumors

Neuroendocrine tumors (NETs) are rare, slow-growing neoplasms characterized by their ability to store and secrete different peptides and neuroamines. Some of these substances cause specific clinical syndromes whereas others are not associated with specific syndromes or symptom complexes. NETs usually have episodic expression that makes diagnosis difficult, erroneous, and often late. For these reasons a high index of suspicion is needed, and it is important to understand the pathophysiology of each tumor to decide which biochemical markers are more useful and when they should be used.