Impact of fluorodihydroxyphenylalanine-18F positron emission tomography on management of adult patients with documented or occult digestive endocrine tumors

High Tumor Uptake on 18F-FDOPA PET/CT Indicates Poor Prognosis in Patients with Metastatic Midgut Neuroendocrine Tumors: A Study from the Groupe d'étude des Tumeurs Endocrines and ENDOCAN-RENATEN Network

PET/CT with 6-18F-fluoro-l-dopa (18F-FDOPA) has high diagnostic performance for midgut neuroendocrine tumors (NETs). We explored the prognostic role of 18F-FDOPA PET/CT uptake in metastatic midgut NETs. Methods: We included, in a test cohort (n = 166) and a full external validation cohort (n = 86), all consecutive patients with metastatic midgut NETs who underwent 18F-FDOPA PET/CT in 5 expert centers from 2010 to 2021. We measured the maximal uptake (SUVmax and SUVpeak) of the tumor and nontumor liver on each 18F-FDOPA PET/CT scan. We measured overall survival (OS) from the time of PET/CT and assessed prognostic factors using Kaplan-Meier and multivariable Cox proportional-hazards analyses in the test cohort, with replication in the validation cohort. Results: Patients had similar characteristics in both cohorts. In the test cohort, median follow-up was 60.3 mo. Patients with an SUVpeak tumor-to-liver (T/L) ratio of more than 4.2 had significantly shorter survival than those with a ratio of 4.2 or less (P = 0.01), with a 5-y OS rate of 74.1% ± 4.5% versus 95% ± 3.4%, respectively. On multivariable analysis, an SUVpeak T/L ratio of more than 4.2 remained associated with shorter OS (hazard ratio, 2.30; 95% CI, 1.02-5.22; P = 0.046) after adjustment for age, grade, number of previous lines, number of metastatic sites, and presence of carcinoid syndrome. In the validation cohort, the 5-y OS rate was 100% versus 57.8% ± 12.5% in patients with an SUVpeak T/L ratio ≤ 4.2 or > 4.2, respectively (P = 0.075). An increasing SUVpeak T/L ratio over time tended to have a pejorative prognostic impact. Conclusion: Tumor uptake on 18F-FDOPA PET/CT is an independent prognostic factor in patients with metastatic midgut NETs.

PET/CT and PET/MRI in neuroendocrine neoplasms

Advanced molecular imaging has come to play an integral role in the management of gastro-entero-pancreatic neuroendocrine neoplasms (GEP-NENs). Somatostatin receptor (SSTR) PET has now emerged as the reference standard for the evaluation of NENs and is particularly critical in the context of peptide receptor radionuclide therapy (PRRT) eligibility. SSTR PET/MRI with liver-specific contrast agent has a strong potential for one-stop-shop multiparametric evaluation of GEP-NENs. 18F-FDG is a complementary radiotracer to SSTR, especially in the context of high-grade neuroendocrine neoplasms. Knowledge gaps in quantitative evaluation of molecular imaging studies and their role in assessment of response to PRRT and combination therapies are active research areas. Novel radiotracers have the potential to overcome existing limitations in the molecular imaging of GEP-NENs. The purpose of this article is to provide an overview of the current trends, pitfalls, and recent advancements of molecular imaging for GEP-NENs.

Bone metastases in midgut neuroendocrine tumors: imaging characteristics, distribution, and risk factors

PURPOSE

Bone metastases (BM) affect 10-30% of patients with small intestine neuroendocrine tumors (siNET), but little descriptive data are available regarding their distribution throughout the skeleton or potential risk factors. Aim of the study is to better describe the imaging characteristics, distribution, and risk factors of siNET bone metastases using 18F-FDOPA PET/CT.

METHODS

All patients with well-differentiated siNET who underwent an 18F-DOPA PET/CT examination in our institution were retrospectively screened between October 2017 and February 2020. Location, SUVmax and CT density of each BM were collected. Sex, metabolic tumor volume (MTV) excluding bone, and metastatic sites other than bone were studied to determine risk factors of BM.

RESULTS

Among the 69 patients included, 11 patients (15.9%) presented BM on 18F-FDOPA (65 metastases). The most frequently involved sites were: thoracic spine, pelvic bones and ribs. About 64% of patients presented multiple BM. On coupled CT scan, 63% of BM were not visible. Using an optimal threshold of 19.2 ml, MTV was an independent predictor of BM (p = 0.004) with a derived sensitivity of 100% [65.0-100.0] and a specificity of 70.9% [57.7-81.2]. Hepatic metastatic involvement was also a significant predictor of BM (p = 0.044).

CONCLUSION

The development of BM in siNETs appears to be a late event, occurring in patients with a high tumor burden and hepatic involvement. They are often multiple and predominate in the axial skeleton.

Molecular Imaging of Neuroendocrine Neoplasms

The key for molecular imaging is the use of a radiotracer with a radioactive and a functional component. While the functional component targets a specific feature of the tumor, the radioactive component makes the target visible. Neuroendocrine neoplasms (NEN) are a diverse group of rare tumors that arise from neuroendocrine cells found mainly in the gastroenteropancreatic system, lung, thyroid, and adrenal glands. They are characterized by the expression of specific hormone receptors on the tumor cell surface, which makes them ideal targets for radiolabeled peptides. The most commonly expressed hormone receptors on NEN cells are the somatostatin receptors. They can be targeted for molecular imaging with various radiolabeled somatostatin analogs, but also with somatostatin antagonists, which have shown improved imaging quality. 18F-DOPA imaging has become a second-line imaging modality in NENs, with the exception of the evaluation of advanced medullary thyroid carcinoma. Alternatives for NENs with insufficient somatostatin receptor expression due to poor differentiation involve targeting glucose metabolism, which can also be used for prognosis. For the localization of the often-small insulinoma, glucagon-like peptide-1 (GLP-1) receptor imaging has become the new standard. Other alternatives involve metaiodobenzylguanidine and the molecular target C-X-C motif chemokine receptor-4. In addition, new radiopeptides targeting the fibroblast activation protein, the glucose-dependent insulinotropic polypeptide receptor and cholecystokinin-2 receptors have been identified in NENs and await further evaluation. This mini-review aims to provide an overview of the major molecular imaging modalities currently used in the field of NENs, and also to provide an outlook on future developments.

Current updates and future directions in diagnosis and management of gastroenteropancreatic neuroendocrine neoplasms

Gastroenteropancreatic neuroendocrine neoplasms are a heterogenous group of rare neoplasms that are increasingly being discovered, often incidentally, throughout the gastrointestinal tract with varying degrees of activity and malignant potential. Confusing nomenclature has added to the complexity of managing these lesions. The term carcinoid tumor and embryonic classification have been replaced with gastroenteropancreatic neuroendocrine neoplasm, which includes gastrointestinal neuroendocrine and pancreatic neuroendocrine neoplasms. A comprehensive multidisciplinary approach is important for clinicians to diagnose, stage and manage these lesions. While histological diagnosis is the gold standard, recent advancements in endoscopy, conventional imaging, functional imaging, and serum biomarkers complement histology for tailoring specific treatment options. In light of developing technology, our review sets out to characterize diagnostic and therapeutic advancements for managing gastroenteropancreatic neuroendocrine tumors, including innovations in radiolabeled peptide imaging, circulating biomarkers, and endoscopic treatment approaches adapted to different locations throughout the gastrointestinal system.

Current status and future prospects of PET-imaging applications in patients with gastro-entero-pancreatic neuroendocrine tumors (GEP-NETs)

Gastro-entero-pancreatic neuroendocrine tumors (GEP-NETs) represent a heterogeneous group of rare neoplasms with increasing incidence over the last decades. Localization of GEP-NETs and their metastases is a vital component for the implementation of accurate and patient-tailored treatment strategies. Addressing this challenge requires the employment of multidisciplinary imaging approaches, with hybrid positron emission tomography/computed tomography (PET/CT) imaging techniques standing at the forefront of this effort. GEP-NETs exhibit several pathophysiologic characteristics, which can serve as highly specific molecular targets that can be effectively visualized and quantified by means of PET-radiopharmaceuticals, facilitating diagnosis, accurate staging and efficient monitoring of treatment response. Furthermore, the capability for whole-body, in-vivo, non-invasive characterization of the molecular heterogeneity of the disease, provides strong prognostic information, while enabling the selection of patients suitable for precision-based theranostic approaches. The dual tracer (¹⁸F-FDG & ⁶⁸Ga-DOTA-peptides) PET/CT imaging approach is the current optimal diagnostic imaging strategy, since it enables tumor localization, accurate staging, non-invasive whole-body total tumor burden characterization of disease heterogeneity, while providing strong prognostic information and guidance towards treatment strategy. Moreover, ⁶⁴Cu-DOTATATE has been recently approved by FDA for SSTRs positive NETs, promising substantial diagnostic and logistical benefits. Furthermore, ¹⁸F-DOPA offers diagnostic capabilities for serotonin-secreting GEP-NETs which are not characterized by cell-surface over-expression of somatostatin receptors (SSTRs) and cannot be seen on morphological imaging. In addition, PET/CT with agents targeting the expression of glucagon-like peptide-1 receptor (GLP-R1) should be considered in cases of clinical suspicion for insulinomas that cannot be detected by morphological imaging or STTRs PET/CT imaging.

Comparison of 18F-DOPA Versus 68Ga-DOTATOC as Preferred PET Imaging Tracer in Well-Differentiated Neuroendocrine Neoplasms

PURPOSE

The aim of this study was to retrospectively compare 18F-FDOPA versus 68Ga-DOTATOC PET in lesion detection rates and laboratory tumor markers in patients with neuroendocrine neoplasms (NENs).

PATIENTS AND METHODS

All patients with histologically proven NEN between May 2015 and February 2019 were included who underwent both 18F-DOPA and 68Ga-DOTATOC PET scans within 6 months from each other (mean, 75; median, 38; range, 2-168 days). All patients, except those with pancreatic NEN, received carbidopa before 18F-DOPA PET. Based on the number of lesions on both modalities, patients were divided into 3 categories: more lesions on 18F-DOPA (DOPA > DOTA), more lesions on 68Ga-DOTATOC (DOTA > DOPA), and equal number of lesions (DOPA = DOTA). Tumor markers chromogranin A, serotonin, and 5-hydroxyindoleacetic acid (5-HIAA) within a maximum of 3 months around either scan were retrieved from the patients' charts.

RESULTS

18F-DOPA revealed significantly more lesions compared with 68Ga-DOTATOC (611 vs 385, P < 0.05). Twenty-four patients were included in the DOPA > DOTA group with 16 small intestinal (SI) NENs, 3 large intestinal, 4 pancreatic, and 1 tumor of unknown origin (TUO). For the 9 patients in the DOTA > DOPA group, 4 were SI, 2 pancreatic, 1 lung, and 2 TUOs. Twelve patients in the DOPA = DOTA group had 6 pancreatic tumors, 3 SI, 1 ovarian, and 2 TUOs. Only serotonin and 5-HIAA showed significant higher values for DOPA > DOTA compared with DOTA > DOPA (mean 24 vs 4, P < 0.05, and 320 vs 81, P < 0.05, respectively). Cutoff values of 20 nmol/109 for serotonin, 185 μg/L for chromogranin A, and 200 nmol/L for 5-HIAA were found to include almost exclusively DOPA > DOTA patients.

CONCLUSIONS

There is an advantage of carbidopa pretreated 18F-DOPA over 68Ga-DOTATOC PET, especially for large intestinal NENs with high levels of biomarkers. There seems to be a relationship between increased biomarker value and improved lesion detection rates with the 18F-DOPA PET scan, which requires further prospective analysis.

Head-to-Head Comparison of 18F-DOPA PET/CT and 68Ga-DOTANOC PET/CT in Patients With Midgut Neuroendocrine Tumors

PURPOSE

The aim of this study was to compare retrospectively 18F-DOPA PET/CT versus 68Ga-DOTANOC PET/CT in a group of patients affected by midgut NET.

PATIENTS AND METHODS

Patients with histologically proven grade 1 or grade 2 midgut NET were explored after injection of 150 MBq of 68Ga-DOTANOC and 210 MBq of 18F-DOPA. The PET/CTs were analyzed visually and semiquantitatively at the patient level, regional level (7 defined regions), and lesion level (maximum of 5 lesions/organ). The criterion standard was determined on the basis of histology and imaging follow-up.

RESULTS

Thirty patients (17 males and 13 females; median age, 63.5 years [37-82 years]) were included. Both PET/CTs were negative in 3 patients and positive in 25 patients. PET/CTs were discordant in 2 patients, with 18F-DOPA positive and 68Ga-DOTANOC negative. 18F-DOPA PET/CT detected more involved regions and more metastatic lesions than 68Ga-DOTANOC PET/CT in 6 (20%) and 10 (33.3%) patients, respectively. Of the 81 confirmed affected regions, 77 (95%) were detected by 18F-DOPA PET/CT and 71 (87.7%) by 68Ga-DOTANOC PET/CT (P < 0.0001). 18F-DOPA PET/CT detected significantly more lesions (211/221) than 68Ga-DOTANOC PET/CT (195/221), corresponding to a sensitivity of 95.5% and 88.2%, respectively (P < 0.0001). Tumor-to-background ratios were more favorable in liver for 18F-DOPA than for 68Ga-DOTANOC. Interestingly, a correlation was found between 18F-DOPA SUVmax and tumor burden and especially with the number of regions involved by the disease (P = 0.019).

CONCLUSIONS

18F-DOPA PET/CT is superior to 68Ga-DOTANOC PET/CT for the detection of lesions, and when available, this tracer may be recommended as the first-line examination for an accurate staging of midgut NET.

Prognostic impact of bone metastases detected by 18F-DOPA PET in patients with metastatic midgut neuroendocrine tumors

OBJECTIVES

Bone metastases (BM) may influence negatively the prognosis of midgut neuroendocrine tumors (NET). The diagnostic sensitivity of ¹⁸F-DOPA PET for midgut NET and associated metastases is high. This study aimed to assess the prognostic impact of BM detected by ¹⁸F-DOPA PET in metastatic midgut NET.

METHODS

All patients with a metastatic midgut NET, who underwent a ¹⁸F-DOPA PET between June 2011 and June 2018, were included. BM were defined following imaging criteria and were classified as poly-BM or oligo-BM, according to their number (< 5 or ≥ 5, respectively). The variables associated with the presence of BM were evaluated by logistic regression. The factors associated with overall survival were explored by Cox regression models.

RESULTS

Among 155 patients included, 46 had BM (29.7%). A carcinoid syndrome (OR 2.96, p = 0.009) and ≥ 3 extra-skeletal metastatic organs (OR 4.99, p = 0.002) were independently associated with the presence of BM. BM were mainly osteoblastic (78%), rarely symptomatic (8.9%), and had a short-term therapeutic impact for 3 patients (6.5%). The presence of BM (HR 2.67, p = 0.034), older age (HR 1.07, p = 0.016), and higher Ki67 (HR 1.09, p = 0.025) were independent prognostic factors. Unlike poly-BM (HR 1.92, p = 0.007), oligo-BM was not a poor prognosis factor (HR 0.77, p = 0.699) compared to the group without BM.

CONCLUSION

¹⁸F-DOPA PET frequently detects BM in patients with metastatic midgut NET. BM have a negative prognostic impact, especially poly-BM. Conversely, oligo-BM do not influence the prognosis and may not impact therapeutic decisions.

KEY POINTS

• ¹⁸F-DOPA PET detected bone metastases in 46 (29.7%) of 155 patients with metastatic midgut neuroendocrine tumors. • Bone metastases have a negative prognostic impact in metastatic midgut neuroendocrine tumors. • Bone oligo-metastases (< 5) do not influence the prognosis and may not impact therapeutic decisions.

Surgery and Perioperative Management in Small Intestinal Neuroendocrine Tumors

Small-intestinal neuroendocrine tumors (SI-NETs) are the most prevalent small bowel neoplasms with an increasing frequency. In the multimodal management of SI-NETs, surgery plays a key role, either in curative intent, even if R0 resection is feasible in only 20% of patients due to advanced stage at diagnosis, or palliative intent. Surgeons must be informed about the specific surgical management of SI-NETs according to their hormonal secretion, their usual dissemination at the time of diagnosis and the need for bowel-preserving surgery to avoid short bowel syndrome. The aim of this paper is to review the surgical indications and techniques, and perioperative and postoperative management of SI-NETs.

Digestive Neuroendocrine Neoplasms (NEN): French Intergroup clinical practice guidelines for diagnosis, treatment and follow-up (SNFGE, GTE, RENATEN, TENPATH, FFCD, GERCOR, UNICANCER, SFCD, SFED, SFRO, SFR)

INTRODUCTION

This document is a summary of the French Intergroup guidelines regarding the management of digestive neuroendocrine neoplasms (NEN) published in February 2020 (www.tncd.org).

METHODS

All French medical societies involved in the management of NEN took part in this work. Recommendations were graded into four categories (A, B, C or D), according to the level of evidence found in the literature until May 2019.

RESULTS

The management of NEN is challenging because of their heterogeneity and the increasing complexity of diagnostic and therapeutic procedures. Pathological analysis is required for their diagnostic and prognostic characterization, which mainly relies on differentiation, grade and stage. The two main emergency situations are functioning syndromes and poorly-differentiated carcinoma. Chromogranin A is the main biochemical marker of NET, although of limited clinical interest. Initial characterization relies on morphological and isotopic imaging. The treatment of localized NET relies on watchful follow-up and local or surgical resection depending on its supposed aggressiveness. Treatment options for metastatic disease include surgery, somatostatin analogues, chemotherapy, targeted therapies, organ-driven locoregional therapies and peptide-receptor radionuclide therapy. As specific predictive factors of treatment efficacy are yet to be identified and head-to-head comparisons have not or only rarely been performed, the therapeutic strategy currently depends on prognostic factors. Cumulative toxicity and the impact of treatment on quality of life must be considered since survival is relatively long in most patients with NET.

CONCLUSION

These guidelines are proposed to achieve the most beneficial therapeutic strategy in clinical practice as the therapeutic landscape of NEN is becoming ever more complex. These recommendations are permanently being reviewed.

Novel PET tracers: added value for endocrine disorders

Nuclear medicine has been implicated in the diagnosis and treatment of endocrine disorders for several decades. With recent development of PET tracers, functional imaging now plays a major role in endocrine tumors enabling with high performance to their localization, characterization, and staging. Besides ¹⁸F-FDG, which may be used in the management and follow-up of endocrine tumors, new tracers have emerged, such as ¹⁸F-DOPA for neuroendocrine tumors (NETs) (medullary thyroid carcinoma, pheochromocytomas and paragangliomas and well-differentiated NETs originating from the midgut) and ¹⁸F-Choline in the field of primary hyperparathyroidism. Moreover, some peptides such as somatostatin analogs can also be used for peptide receptor radionuclide therapy. In this context, Gallium-68 labeled somatostatin analogs (⁶⁸Ga-SSA) can help to tailor therapeutic choices and follow the response to treatment in the so-called "theranostic" approach. This review emphasizes the usefulness of these three novel PET tracers (¹⁸F-Choline, ¹⁸F-FDOPA, and ⁶⁸Ga-SSA) for primary hyperparathyroidism and neuroendocrine tumors.

Gastroenteropancreatic neuroendocrine tumors: recommendations of Turkish multidisciplinary neuroendocrine tumor study group on diagnosis, treatment and follow-up

Gastroenteropancreatic neuroendocrine tumors (GEPNETs) are a relatively rare, heterogeneous group of diseases in which important advances have been observed in the diagnosis and treatment as well as in our understanding of the biology and genetics of the disease in recent years. Given the insufficient scientific data available on evidence-based management of GEPNETs and the differences in circumstances in individual countries, a multidisciplinary study group was established to provide guidelines for the management of GEPNETS. This study group consisted of a medical oncologist, endocrinologist, surgeon, pathologist, gastroenterologist, and a nuclear medicine specialist, who aimed to prepare a practical guide in the light of existing scientific data and international guidelines, to be used in common clinical practice.

Molecular Imaging of Gastroenteropancreatic Neuroendocrine Tumors: Current Status and Future Directions

Through diagnostic imaging and peptide receptor radionuclide therapy, nuclear medicine has earned a major role in gastroenteropancreatic neuroendocrine tumors (GEP NETs). GEP NETs are diagnosed fortuitously or on the basis of symptoms or hormonal syndrome. The functional tumor characteristics shown by radionuclide imaging allow for more accurate staging and treatment selection. Tumor grade helps determine which tracer should be selected. In the past, ¹¹¹In-pentetreotide has been successful in well-differentiated (G1 and G2) tumors. However, PET/CT imaging with novel somatostatin analogs (e.g., ⁶⁸Ga-DOTATOC, ⁶⁸Ga-DOTATATE, ⁶⁸Ga-DOTANOC, and ⁶⁴Cu-DOTATATE) now offers improved sensitivity. ¹⁸F-fluorodihydroxyphenylalanine (¹⁸F-FDOPA) is another interesting radiopharmaceutical. ¹⁸F-FDOPA sensitivity is influenced by a tumor's capacity to take up, decarboxylate, and store amine precursors. ¹⁸F-FDOPA sensitivities are highest in ileal NETs and may also be helpful in insulinomas. A high uptake of ¹⁸F-FDG with a low uptake of somatostatin analog usually indicates poorly differentiated tumors (G3). Starting from these principles, this article discusses theranostic approaches to GEP NETs, taking into account both primary and metastatic lesions.

Carbidopa-assisted 18F-fluorodihydroxyphenylalanine PET/CT for the localization and staging of non-functioning neuroendocrine pancreatic tumors

OBJECTIVE

CD premedication was found to increase the value of ¹⁸F-fluorodihydroxyphenylalanine (¹⁸F-FDOPA) PET/CT imaging in the detection of adult insulinoma. The aim of this study was to evaluate the performance of CD-assisted ¹⁸F-FDOPA PET/CT in the diagnosis and staging of non-functioning pNETs.

METHODS

Twenty consecutive patients with low-grade pNETs who underwent CD-assisted ¹⁸F-FDOPA PET/CT imaging and ¹¹¹In-somatostatin receptor scintigraphy (SRS) were evaluated. Histology was considered as the gold standard. In case where no surgical resection was performed, the diagnosis of pNET was made by the confrontation of the different available imaging modalities.

RESULTS

CD-assisted ¹⁸F-FDOPA PET/CT was positive in 18/20 cases (90 %), whereas SRS was positive in 13/19 cases (68 %). When considered the 19 patients underwent both nuclear medicine examinations, ¹⁸F-FDOPA PET/CT was significantly more sensitive then SRS for primary tumor detection (p = 0.049). False-negative results of both ¹⁸F-FDOPA PET/CT and SRS were observed in 2 cystic pNETs. SRS failed to detect one additional cystic tumor and 3 pNETs of 10, 12 and 17 mm, respectively. ¹⁸F-FDOPA PET/CT correctly identified all patients with lymphatic, visceral and bone metastases. SRS failed to detect lymphatic spread and was falsely negative in one patient with splenic metastasis.

CONCLUSIONS

Contrary to widely held assumptions, our study further expands the application of CD-assisted ¹⁸F-FDOPA PET/CT for non-functioning pNETs when ⁶⁸Ga-radiolabeled somatostatin analogs are not available.

Transcriptomic and Immunohistochemical Profiling of SLC6A14 in Pancreatic Ductal Adenocarcinoma

We used a target-centric strategy to identify transporter proteins upregulated in pancreatic ductal adenocarcinoma (PDAC) as potential targets for a functional imaging probe to complement existing anatomical imaging approaches. We performed transcriptomic profiling (microarray and RNASeq) on histologically confirmed primary PDAC tumors and normal pancreas tissue from 33 patients, including five patients whose tumors were not visible on computed tomography. Target expression was confirmed with immunohistochemistry on tissue microarrays from 94 PDAC patients. The best imaging target identified was SLC6A14 (a neutral and basic amino acid transporter). SLC6A14 was overexpressed at the transcriptional level in all patients and expressed at the protein level in 95% of PDAC tumors. Very little is known about the role of SLC6A14 in PDAC and our results demonstrate that this target merits further investigation as a candidate transporter for functional imaging of PDAC.

Role of (18) F-FDOPA PET/CT imaging in endocrinology

(18) F-FDOPA (6-[18F]-L-fluoro-L-3, 4-dihydroxyphenylalanine)-based PET/CT imaging can be a useful tool for the detection of different neuroendocrine tumours (NETs). (18) F-FDOPA is taken up into the cells via the neutral amino acid transporter (LAT1/4F2hc). This transporter is also coupled to the mammalian target of rapamycin (mTOR) signalling pathway. (18) F-FDOPA PET/CT may be performed for confirmation of diagnosis of pheochromocytoma/paraganglioma, staging at initial presentation, restaging and follow-up of patients. In SDHx-related syndromes, (18) F-FDG PET/CT should be performed in addition to (18) F-FDOPA PET/CT. (18) F-FDOPA PET/CT is also invaluable in the detection staging/restaging of carcinoid tumours and has greater sensitivity as compared to somatostatin receptor scintigraphy. (18) F-FDOPA PET/CT can also distinguish between focal vs diffuse CHI. It is not as useful in adult hyperinsulinism due to increased background uptake, but the problem may be overcome with the help of premedication with carbidopa. It has limited use in pancreatic NETs. (18) F-FDOPA PET/CT is a good modality for detection of persistent and residual medullary thyroid cancer (MTC), but (18) F-FDG PET/CT may be needed in aggressive tumours. In summary, F-DOPA PET/CT has widespread utility in the diagnosis of different neuroendocrine tumours.

Evaluating digestive neuroendocrine tumor progression and therapeutic responses in the era of targeted therapies: state of the art

Well-differentiated neuroendocrine tumors (NETs) are a group of heterogeneous rare tumors. They are often slow-growing and patients can have very long survival, even at the metastatic stage. The evaluation of tumor progression and therapeutic responses is currently based on Response Evaluation Criteria In Solid Tumors v1.1 (RECIST) criteria. As for other malignancies, RECIST criteria are being reexamined for NETs in the era of targeted therapies because tumor response to targeted therapies is rarely associated with shrinkage, as opposed to prolonged progression-free survival. Therefore, size-based criteria no longer seem to be suitable to the assessment of NET progression and therapeutic responses, especially considering targeted therapies. New imaging criteria, combining morphological and functional techniques, have proven relevant for other malignancies treated with targeted therapies. To date, such studies have rarely been conducted on NETs. Moreover, optimizing the management of NET patients also requires considering clinical, biological, and pathological aspects of tumor evolution. Our objectives herein were to comprehensively review current knowledge on the assessment of tumor progression and early prediction of therapeutic responses and to broaden the outlook on well-differentiated NETs, in the era of targeted therapies.

18F-fluorodihydroxyphenylalanine PET/CT in patients with neuroendocrine tumors of unknown origin: relation to tumor origin and differentiation

This work was performed to evaluate the performance of (18)F-fluorodihydroxyphenylalanine ((18)F-FDOPA) PET/CT in detecting primary neuroendocrine tumors (NETs) occult on morphologic and functional imaging, in relation to tumor origin and differentiation.

METHODS

A retrospective study of NET patients who were investigated with (18)F-FDOPA PET/CT imaging in 2 academic endocrine tumor centers was conducted. Only patients with negative conventional and somatostatin receptor scintigraphy (SRS) results were studied.

RESULTS

Twenty-seven patients were evaluated with (18)F-FDOPA PET/CT, 23 at their initial staging and 4 during their follow-up. The primary occult NET was localized by (18)F-FDOPA PET/CT in 12 patients (overall sensitivity, 44%; 52% in patients evaluated at initial diagnosis), leading to tumor resection in all cases. The primary tumors were distributed and graded as follows: 1 duodenum G2 lesion, 7 ileum G2 lesions, 2 terminal ileum G1 lesions, 1 pancreas G2 lesion, and 1 gallbladder G3 lesion. Patients with positive (18)F-FDOPA PET/CT results had higher values of serum chromogranin A (100% vs. 20%, P = 0.0003), serotonin, or urinary 5-hydroxyindolacetic acid (83% vs. 20%, P = 0.003). Two false-negative results were related to poorly differentiated duodenal and prostatic NETs (G3). (18)F-FDOPA PET/CT showed more metastatic anatomic regions than SRS in 17 patients.

CONCLUSION

(18)F-FDOPA PET appears to be a sensitive functional imaging tool for the detection of primary NETs occult on SRS, especially tumors with a well-differentiated pattern and serotonin secretion.

Enzyme inhibition of dopamine metabolism alters 6-[18F]FDOPA uptake in orthotopic pancreatic adenocarcinoma

Background

An unknown location hampers removal of pancreatic tumours. We studied the effects of enzyme inhibitors on the uptake of 6-[¹⁸F]fluoro-l-3,4-dihydroxyphenylalanine ([¹⁸F]FDOPA) in the pancreas, aiming at improved imaging of pancreatic adenocarcinoma.

Methods

Mice bearing orthotopic BxPC3 pancreatic adenocarcinoma were injected with 2-deoxy-2-[¹⁸F]fluoro-d-glucose ([¹⁸F]FDG) and scanned with positron emission tomography/computed tomography (PET/CT). For [¹⁸F]FDOPA studies, tumour-bearing mice and sham-operated controls were pretreated with enzyme inhibitors of aromatic amino acid decarboxylase (AADC), catechol-O-methyl transferase (COMT), monoamine oxidase A (MAO-A) or a combination of COMT and MAO-A. Mice were injected with [¹⁸F]FDOPA and scanned with PET/CT. The absolute [¹⁸F]FDOPA uptake was determined from selected tissues using a gamma counter. The intratumoural biodistribution of [¹⁸F]FDOPA was recorded by autoradiography. The main [¹⁸F]FDOPA metabolites present in the pancreata were determined with radio-high-performance liquid chromatography.

Results

[¹⁸F]FDG uptake was high in pancreatic tumours, while [¹⁸F]FDOPA uptake was highest in the healthy pancreas and significantly lower in tumours. [¹⁸F]FDOPA uptake in the pancreas was lowest with vehicle pretreatment and highest with pretreatment with the inhibitor of AADC. When mice received COMT + MAO-A inhibitors, the uptake was high in the healthy pancreas but low in the tumour-bearing pancreas.

Conclusions

Combined use of [¹⁸F]FDG and [¹⁸F]FDOPA is suitable for imaging pancreatic tumours. Unequal pancreatic uptake after the employed enzyme inhibitors is due to the blockade of metabolism and therefore increased availability of [¹⁸F]FDOPA metabolites, in which uptake differs from that of [¹⁸F]FDOPA. Pretreatment with COMT + MAO-A inhibitors improved the differentiation of pancreas from the surrounding tissue and healthy pancreas from tumour. Similar advantage was not achieved using AADC enzyme inhibitor, carbidopa.

18F-fluorodihydroxyphenylalanine vs other radiopharmaceuticals for imaging neuroendocrine tumours according to their type

6-Fluoro-(¹⁸F)-L-3,4-dihydroxyphenylalanine (FDOPA) is an amino acid analogue for positron emission tomography (PET) imaging which has been registered since 2006 in several European Union (EU) countries and by several pharmaceutical firms. Neuroendocrine tumour (NET) imaging is part of its registered indications. NET functional imaging is a very competitive niche, competitors of FDOPA being two well-established radiopharmaceuticals for scintigraphy, ¹²³I-metaiodobenzylguanidine (MIBG) and ¹¹¹In-pentetreotide, and even more radiopharmaceuticals for PET, including fluorodeoxyglucose (FDG) and somatostatin analogues. Nevertheless, there is no universal single photon emission computed tomography (SPECT) or PET tracer for NET imaging, at least for the moment. FDOPA, as the other PET tracers, is superior in diagnostic performance in a limited number of precise NET types which are currently medullary thyroid cancer, catecholamine-producing tumours with a low aggressiveness and well-differentiated carcinoid tumours of the midgut, and in cases of congenital hyperinsulinism. This article reports on diagnostic performance and impact on management of FDOPA according to the NET type, emphasising the results of comparative studies with other radiopharmaceuticals. By pooling the results of the published studies with a defined standard of truth, patient-based sensitivity to detect recurrent medullary thyroid cancer was 70 % [95 % confidence interval (CI) 62.1–77.6] for FDOPA vs 44 % (95 % CI 35–53.4) for FDG; patient-based sensitivity to detect phaeochromocytoma/paraganglioma was 94 % (95 % CI 91.4–97.1) for FDOPA vs 69 % (95 % CI 60.2–77.1) for ¹²³I-MIBG; and patient-based sensitivity to detect midgut NET was 89 % (95 % CI 80.3–95.3) for FDOPA vs 80 % (95 % CI 69.2–88.4) for somatostatin receptor scintigraphy with a larger gap in lesion-based sensitivity (97 vs 49 %). Previously unpublished FDOPA results from our team are reported in some rare NET, such as small cell prostate cancer, or in emerging indications, such as metastatic NET of unknown primary (CUP-NET) or adrenocorticotropic hormone (ACTH) ectopic production. An evidence-based strategy in NET functional imaging is as yet affected by a low number of comparative studies. Then the suggested diagnostic trees, being a consequence of the analysis of present data, could be modified, for some indications, by a wider experience mainly involving face-to-face studies comparing FDOPA and ⁶⁸Ga-labelled peptides.

Hepatocellular carcinoma and gastroenteropancreatic neuroendocrine tumors: potential role of other positron emission tomography radiotracers

18F-Fluorodeoxyglucose avidity for gastroenteropancreatic neuroendocrine tumors and hepatocellular carcinoma is variable, depending on the underlying tumor biology. Experience with non-fluorodeoxyglucose (FDG) tracers (eg, 18F-labeled amine precursors l-dihydroxyphenylalanine and 68Ga-DOTA-peptides for gastroenteropancreatic neuroendocrine tumors and radiolabeled acetate or choline for hepatocellular carcinoma) is evolving and expanding rapidly. This article reviews the role of FDG and non-FDG radiotracers in the imaging evaluation of patients with gastroenteropancreatic neuroendocrine tumors or hepatocellular carcinoma.

PET/CT using ¹⁸F-FDOPA provides improved staging of carcinoid tumor patients in a Canadian setting

AIM

In Canada, staging of carcinoid tumors is largely based on computed tomography (CT) imaging sometimes complemented with somatostatin receptor scintigraphy (SRS). This study assessed the diagnostic accuracy of 6-[¹⁸F]fluoro-3,4-dihydroxyphenylalanine (¹⁸F-FDOPA) PET/CT in neuroendocrine tumors.

METHODS

We prospectively included 27 patients with either suspected carcinoid (n=6, with all prior tests negative) or with an established diagnosis of intestinal carcinoid tumor (n=21) from two Canadian treatment centers. Findings of ¹⁸F-FDOPA PET/CT were compared with SRS, CT, and combined SRS/CT using a composite reference standard comprising all available imaging, biochemistry, surgery, and follow-up data. Sensitivity was calculated per patient, per body region, and per lesion. The contribution to patient management was estimated from the feedback of attending physicians.

RESULTS

In documented carcinoid patients, ¹⁸F-FDOPA PET/CT identified disease in 20 of 21 patients (patient-based sensitivity 95%). In 56 positive regions, ¹⁸F-FDOPA PET/CT detected 53, CT detected 34, SRS detected 34, and CT+SRS detected 39 regions, leading to region-based sensitivities of 95, 61, 62, and 71%, respectively. Lesion-based sensitivities were 96, 69, 50, and 72%, respectively. In the six patients with suspected disease only, one CT scan was positive, but ¹⁸F-FDOPA PET/CT was negative for all. ¹⁸F-FDOPA PET contributed to patient management in 12/21 patients (57%).

CONCLUSION

¹⁸F-FDOPA PET/CT proved to be an excellent modality for staging of carcinoid tumor patients, with superior performance compared with currently applied methods in Canada. In patients with suspected disease with negative prior imaging investigations, ¹⁸F-FDOPA was not helpful.

Standard imaging techniques for neuroendocrine tumors

Several diagnostic imaging techniques have been used successfully for evaluating patients with neuroendocrine tumors (NETs). These techniques include computed tomography (CT), magnetic resonance imaging, positron emission tomography/CT, single-photon emission CT (SPECT), and SPECT/CT. This article reviews the various imaging methods and their respective advantages and limitations for use in different types of NETs, in particular carcinoid tumors.

Molecular imaging of neuroendocrine tumors

Neuroendocrine tumors (NET) are a heterogeneous group of tumors that arise from neuroendocrine cells. These tumors may arise from various organs, including lung, thymus, thyroid, stomach, duodenum, small bowel, large bowel, appendix, pancreas, adrenal, and skin. Most are well differentiated and have the ability to produce biogenic amines and various hormones. NET usually occur sporadically but they also be associated with various familial syndromes. For the vast majority of NET, surgical resection is the treatment of choice whenever feasible. Localization of NET prior to surgery and for staging and follow-up relies on both anatomic and functional imaging modalities. In fact, the unique secretory characteristics of these tumors lend themselves to imaging by molecular imaging modalities, which can target specific metabolic pathways or receptors. Neuroendocrine cells have a variety of such target receptors and pathways for which radiopharmaceuticals have been developed, including [(123)I/(131)I]-metaiodobenzylguanidine (MIBG), [(111)In]pentetreotide, [(68)Ga] somatostatin analogs, [(18)F] fluorodeoxyglucose (FDG), [(11)C/(18)F] dihydroxyphenylalanine (DOPA), [(11)C] 5-hydroxytryptophan (5-HTP) (99m)Tc pentavalent dimercaptosuccinic acid ([(99m)Tc] (V) DMSA, and [(18)F] fluorodopamine (FDA). Here, we review the molecular imaging approaches for NET using various radiopharmaceuticals.

PET and PET/CT in endocrine tumours

Functional information provided by PET tracers together with the superior image quality and the better data quantification by PET technology had a changing effect on the significance of nuclear medicine in medical issues. Recently introduced hybrid PET/CT systems together with the introduction of novel PET radiopharmaceuticals have contributed to the fact that nuclear medicine has become a growing diagnostic impact on endocrinology. In this review imaging strategies, different radiopharmaceuticals including the basic mechanism of their cell uptake, and the diagnostic value of PET and PET/CT in endocrine tumours except differentiated thyroid carcinomas will be discussed.

18F-FDOPA: a multiple-target molecule

Although 6-(18)F-fluoro-L-dopa ((18)F-FDOPA) has been available to study the striatal dopaminergic system for more than 2 decades, the full potential of the tracer was not realized before the introduction of (18)F-FDOPA PET and PET/CT to image a variety of neuroendocrine tumors (NETs) and pancreatic beta-cell hyperplasia. Together with receptor-based imaging, (18)F-FDOPA offers a formerly unforeseen means to assist in the management of NETs and infants with persistent hyperinsulinemic hyperplasia. Institutions with special expertise in surgical, oncologic, and radiologic therapeutic modalities for NETs derive the highest benefit from (18)F-FDOPA PET/CT. (18)F-FDOPA-guided therapy may add to NET control by ensuring maximal cytoreduction.