Receptor radionuclide therapy with 90Y-DOTATOC in patients with medullary thyroid carcinomas

Sporadic Medullary Thyroid Carcinoma: Towards a Precision Medicine

Medullary thyroid carcinoma (MTC) is a neuroendocrine malignant tumor originating from parafollicular C-cells producing calcitonin. Most of cases (75%) are sporadic while the remaining (25%) are hereditary. In these latter cases medullary thyroid carcinoma can be associated (multiple endocrine neoplasia type IIA and IIB) or not (familial medullary thyroid carcinoma), with other endocrine diseases such as pheochromocytoma and/or hyperparathyroidism. RET gene point mutation is the main molecular alteration involved in MTC tumorigenesis, both in sporadic and in hereditary cases. Total thyroidectomy with prophylactic/therapeutic central compartment lymph nodes dissection is the initial treatment of choice. Further treatments are needed according to tumor burden and rate of progression. Surgical treatments and local therapies are advocated in the case of single or few local or distant metastasis and slow rate of progression. Conversely, systemic treatments should be initiated in cases with large metastatic and rapidly progressive disease. In this review, we discuss the details of systemic treatments in advanced and metastatic sporadic MTC, focusing on multikinase inhibitors, both those already used in clinical practice and under investigation, and on emerging treatments such as highly selective RET inhibitors and radionuclide therapy.

Peptide Receptor Radionuclide Therapy in Thyroid Cancer

The treatment options that are currently available for management of metastatic, progressive radioactive iodine (RAI)-refractory differentiated thyroid cancers (DTCs), and medullary thyroid cancers (MTCs) are limited. While there are several systemic targeted therapies, such as tyrosine kinase inhibitors, that are being evaluated and implemented in the treatment of these cancers, such therapies are associated with serious, sometimes life-threatening, adverse events. Peptide receptor radionuclide therapy (PRRT) has the potential to be an effective and safe modality for treating patients with somatostatin receptor (SSTR)+ RAI-refractory DTCs and MTCs. MTCs and certain sub-types of RAI-refractory DTCs, such as Hürthle cell cancers which are less responsive to conventional modalities of treatment, have demonstrated a favorable response to treatment with PRRT. While the current literature offers hope for utilization of PRRT in thyroid cancer, several areas of this field remain to be investigated further, especially head-to-head comparisons with other systemic targeted therapies. In this review, we provide a comprehensive outlook on the current translational and clinical data on the use of various PRRTs, including diagnostic utility of somatostatin analogs, theranostic properties of PRRT, and the potential areas for future research.

Metastatic Medullary Thyroid Cancer: The Role of 68Gallium-DOTA-Somatostatin Analogue PET/CT and Peptide Receptor Radionuclide Therapy

CONTEXT

Metastatic medullary thyroid cancer (MTC) is a rare malignancy with minimal treatment options. Many, but not all, MTCs express somatostatin receptors.

OBJECTIVE

Our aim was to explore the role of 68Ga-DOTA-somatostatin analogue (SSA) positron emission tomography (PET)/computed tomography (CT) in patients with metastatic MTC and to determine their eligibility for peptide receptor radionuclide therapy (PRRT).

METHODS

We retrospectively identified patients with metastatic MTC who had 68Ga-DOTA-SSA PET/CT at 5 centers. We collected characteristics on contrast-enhanced CT, 68Ga-DOTA-SSA and 18F-FDG PET/CT. The efficacy of PRRT was explored in a subgroup of patients. Kaplan-Meier analysis was used to estimate time to treatment failure (TTF) and overall survival (OS).

RESULTS

Seventy-one patients were included (10 local recurrence, 61 distant disease). Of the patients with distant disease, 16 (26%) had ≥50% of disease sites with tracer avidity greater than background liver, including 10 (10/61, 16%) with >90%. In 19 patients with contemporaneous contrast-enhanced CT, no disease regions were independently identified on 68Ga-DOTA-SSA PET/CT. Thirty-five patients had an 18F-FDG PET/CT, with 18F-FDG positive/68Ga-DOTA-SSA negative metastases identified in 15 (43%). Twenty-one patients had PRRT with a median TTF of 14 months (95% CI 8-25) and a median OS of 63 months (95% CI 21-not reached). Of the entire cohort, the median OS was 323 months (95% CI 152-not reached). Predictors of poorer OS included a short calcitonin doubling-time (≤24 months), strong 18F-FDG avidity, and age ≥60 years.

CONCLUSIONS

The prevalence of high tumor avidity on 68Ga-DOTA-SSA PET/CT is low in the setting of metastatic MTC; nevertheless, PRRT may still be a viable treatment option in select patients.

Efficacy and safety of peptide receptor radionuclide therapy in advanced radioiodine-refractory differentiated thyroid cancer and metastatic medullary thyroid cancer: a systematic review

Background

It has been shown that a subgroup of patients with differentiated thyroid cancer (DTC) and medullary thyroid carcinoma (MTC) would progress to advanced stages of thyroid cancer. Therefore, the present study was done to systematically review available evidence in order to investigate efficacy and safety of peptide receptor radionuclide therapy (PRRT) in the patients with advanced radioiodine refractory differentiated thyroid cancer (RR-DTC) and metastatic MTC.

Methods

For this purpose, relevant studies investigated safety and efficacy of PRRT in the patients with advanced RR-DTC and metastatic MTC were identified by searching Medline (Pubmed, Ovid, and Ebsco), Scopus, Embase, Web of Science, and Cochrane Library databases (from database inception to March 24, 2021). The review was performed according to the preferred reporting items for systematic reviews and meta-analyses (PRISMA) statement. Searching was done independently by two investigators. Two researchers independently extracted the data and any disagreement was adjudicated by consensus. Quality of the studies was assessed using the tool of case reports/series in systematic reviews.

Results

Among 2284 related papers, 41 papers met the inclusion criteria. A total of 157 patients with RR-DTC were treated with PPRT. Biochemical and objective responses (partial and complete) were observed in 25.3 and 10.5% of patients, respectively. Among 220 patients with metastatic MTC, biochemical and objective responses were observed in 37.2 and 10.6% of the patients, respectively.

Forty-six deaths were reported in 95 patients with advanced RR-DTC. In addition, 63 deaths were observed in 144 patients with metastatic MTC. Major side effects were reported in 124 patients treated with ⁹⁰Y -based agent. In the patients treated with 177Lu-DOTA-TATE and 111In-Octreotide, mild and transient hematologic or renal complications were reported.

Conclusion

Findings of the study revealed that in the absence of the established treatment for the patients with RR-DTC and metastatic MTC, PRRT could be effective with few adverse events.

Trial registration

PROSPERO registration number: CRD42019125245.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-021-08257-x.

Efficacy and safety of concomitant 177Lu-DOTATATE and low-dose capecitabine in advanced medullary thyroid carcinoma: a single-centre experience

AIMS

Peptide receptor radionuclide therapy (PRRT) has been shown to be useful in inoperable/metastatic medullary thyroid carcinoma (MTC). However, the role of concomitant PRRT and low-dose capecitabine therapy has not yet been studied in these patients. This study was conducted to evaluate the efficacy and safety of this combination approach in advanced MTC.

MATERIALS AND METHODS

This was a retrospective, single-centre study. Data of consecutive patients of advanced inoperable/metastatic MTC treated with concomitant Lu-DOTATATE+capecitabine, from January 2014 to August 2018, were collected and analysed for radiological, molecular and biochemical responses and treatment-related toxicity.

RESULTS

Eight patients with advanced MTC received a median cumulative dose of 20.9 GBq (interquartile range 8.9-27.7 GBq) Lu-DOTATATE over 1-4 cycles and 1250 mg/m capecitabine from days 0 to 14 of each PRRT cycle. Radiological response according to Response Evaluation Criteria in Solid Tumours 1.1 criteria could be assessed in seven patients. Six out of seven patients (86%) had stable disease, while disease progression was observed in 1/7 (14%) patients. However, molecular response, as per the European Organization for Research and Treatment of Cancer criteria, was observed in all the seven patients. Biochemical response with reduction in serum calcitonin levels was observed in 3/5 (60%) patients. With the exception of grade 2 anaemia in one patient, no other significant toxicity was observed in this cohort.

CONCLUSION

Our results indicate the efficacy and safety of concomitant Lu-DOTATATE and capecitabine in advanced MTC. Larger randomized controlled trials are, however, required to establish the role of capecitabine as a radiosensitizer along with PRRT in these patients.

Advances in the Management of Medullary Thyroid Carcinoma: Focus on Peptide Receptor Radionuclide Therapy

Effective treatment options in advanced/progressive/metastatic medullary thyroid carcinoma (MTC) are currently limited. As in other neuroendocrine neoplasms (NENs), peptide receptor radionuclide therapy (PRRT) has been used as a therapeutic option in MTC. To date, however, there are no published reviews dealing with PRRT approaches. We performed an in-depth narrative review on the studies published in this field and collected information on registered clinical trials related to this topic. We identified 19 published studies, collectively involving more than 200 patients with MTC, and four registered clinical trials. Most cases of MTC were treated with PRRT with somatostatin analogues (SSAs) radiolabelled with 90 yttrium (90Y) and 177 lutetium (177Lu). These radiopharmaceuticals show efficacy in the treatment of patients with MTC, with a favourable radiological response (stable disease, partial response or complete response) in more than 60% of cases, coupled with low toxicity. As MTC specifically also expresses cholecystokinin receptors (CCK2Rs), PRRT with this target has also been tried, and some randomised trials are ongoing. Overall, PRRT seems to have an effective role and might be considered in the therapeutic strategy of advanced/progressive/metastatic MTC.

Peptide Receptor Radionuclide Therapy in Patients With Differentiated Thyroid Cancer: A Meta-analysis

PURPOSE

As patients with progressive medullary thyroid cancer (MTC) and radioiodine-refractory metastatic differentiated nonmedullary thyroid cancer (DTC) have poor prognoses and present therapeutic challenges, peptide receptor radionuclide therapy (PRRT) targeting the somatostatin receptor provides a promising option. This meta-analysis evaluated the therapeutic effects and outcomes of PRRT in differentiated thyroid cancer.

PATIENTS AND METHODS

PUBMED, EMBASE, CINAHL, SCOPUS, and COCHRANE were systematically searched using appropriate key words. The primary therapeutic effect was the radiological response after PRRT, and the objective response rate (ORR) and disease control rate (DCR) were identified in MTC and DTC, respectively. The outcome of serious adverse events (grade 3 or 4), additional therapeutic effects of F-FDG PET/CT and biochemical (calcitonin and thyroglobulin) responses, and radionuclides for PRRT were assessed as subgroup analyses. The parameters were generated as pooled proportions.

RESULTS

Eleven articles with 165 patients were included (98 patients with MTC and 67 patients with DTC). PRRT achieved pooled proportions of ORR in 8.53% to 15.61%, DCR in 53.95% to 59.99%, and serious adverse events in 2.79% to 2.82% in MTC and DTC patients. F-FDG PET/CT and biochemical responses revealed similar results as the radiological response. Lu-based PRRT (ORR, 11.48%-24.52%; DCR, 61.47%-67.26%) showed better therapeutic effects than Y-based PRRT (ORR, 6.98%-13.82%; DCR, 50.86%-57.29%).

CONCLUSIONS

This meta-analysis suggests that PRRT could be a potential and safe strategy for MTC and DTC. In particular, PRRT with Lu exhibited improved therapeutic effects relative to PRRT with Y.

Increased therapeutic effect on medullary thyroid cancer using a combination of radiation and tyrosine kinase inhibitors

Since patients with medullary thyroid cancer (MTC) often have metastatic disease at the time of diagnosis, the development of efficient systemic treatment options for MTC is important. Vandetanib and cabozantinib are two tyrosine kinase inhibitors (TKIs) that were recently approved by FDA and EMA for systemic treatment of metastatic MTC. Additionally, since MTC is of a neuroendocrine tumour type, treatment with radiolabelled somatostatin analogues (e.g. ¹⁷⁷Lu-octreotate) is a valid option for patients with MTC. The aim of this study was to investigate the potentially increased therapeutic effect of combining radiation therapy with these TKIs for treatment of MTC in a mouse model. Nude mice carrying patient-derived MTC tumours (GOT2) were treated with external beam radiotherapy (EBRT) and/or one of the two TKIs vandetanib or cabozantinib. The tumour volume was determined and compared with that of mock-treated controls. The treatment doses were chosen to give a moderate effect as monotherapy to be able to detect any increased therapeutic effect from the combination therapy. At the end of follow-up, tumours were processed for immunohistochemical (IHC) analyses. The animals in the combination therapy groups showed the largest reduction in tumour volume and the longest time to tumour progression. Two weeks after start of treatment, the tumour volume for these mice was reduced by about 70–75% compared with controls. Furthermore, also EBRT and TKI monotherapy resulted in a clear anti-tumour effect with a reduced tumour growth compared with controls. The results show that an increased therapeutic effect could be achieved when irradiation is combined with TKIs for treatment of MTC. Future studies should evaluate the potential of using ¹⁷⁷Lu-octreotate therapy in combination with TKIs in patients.

Targeted Therapy for Advanced Thyroid Cancer: Kinase Inhibitors and Beyond

The treatment of advanced thyroid cancer has undergone rapid evolution in the last decade, with multiple kinase inhibitor drug approvals for each subtype of thyroid cancer and a number of other commercially available drugs that have been studied for this indication. Although most of the US Food and Drug Administration (FDA)-approved drugs are antiangiogenic multikinase inhibitors-vandetanib, cabozantinib, sorafenib, lenvatinib-there are two FDA indications that are mutation specific-dabrafenib/trametinib for BRAF-mutated anaplastic thyroid cancer and larotrectinib for NTRK-fusion thyroid cancer. Furthermore, other mutation-specific drugs, immunotherapies, and novel strategies for advanced thyroid cancer are under investigation. Understanding the molecular basis of thyroid cancer, the drugs of interest for treatment of advanced thyroid cancer, and how these drugs can be administered safely and in the appropriate clinical scenario are the topics of this review.

Gemcitabine potentiates the anti-tumour effect of radiation on medullary thyroid cancer

Patients with medullary thyroid cancer (MTC) are often diagnosed with spread tumour disease and the development of better systemic treatment options for these patients is important. Treatment with the radiolabelled somatostatin analogue ¹⁷⁷Lu-octreotate is already a promising option but can be optimised. For example, combination treatment with another substance could increase the effect on tumour tissue. Gemcitabine is a nucleoside analogue that has been shown to sensitise tumour cells to radiation. The aim of this study was to investigate potentially additive or synergistic effects of combining radiation with gemcitabine for treatment of MTC. Nude mice transplanted with patient-derived MTC tumours (GOT2) were divided into groups and treated with radiation and/or gemcitabine. Radiation treatment was given as ¹⁷⁷Lu-octreotate or external beam radiotherapy (EBRT). The volume of treated and untreated tumours was followed. The absorbed dose and amount of gemcitabine were chosen to give moderate tumour volume reduction when given as monotherapy to enable detection of increased effects from combination treatment. After follow-up, the mice were killed and tumours were immunohistochemically (IHC) analysed. Overall, the animals that received a combination of EBRT and gemcitabine showed the largest reduction in tumour volume. Monotherapy with EBRT or gemcitabine also resulted in a clear detrimental effect on tumour volume, while the animals that received ¹⁷⁷Lu-octreotate monotherapy showed similar response as the untreated animals. The GOT2 tumour was confirmed in the IHC analyses by markers for MTC. The IHC analyses also revealed that the proliferative activity of tumour cells was similar in all tumours, but indicated that fibrotic tissue was more common after EBRT and/or gemcitabine treatment. The results indicate that an additive, or even synergistic, effect may be achieved by combining radiation with gemcitabine for treatment of MTC. Future studies should be performed to evaluate the full potential of combining ¹⁷⁷Lu-octreotate with gemcitabine in patients.

SSTR2A expression in medullary thyroid carcinoma is correlated with longer survival

PURPOSE

Medullary thyroid carcinoma (MTC) derives from the parafollicular C-cells of the thyroid gland. Somatostatin receptors (SSTRs) are expressed in various neuroendocrine tumours including MTC. The aim of this study was to evaluate SSTR2A as a prognostic factor for MTC, to study distribution of SSTR2A expression within tumours and to compare expression of SSTR2A between primary tumours and corresponding lymph node metastases.

METHODS

Patients who underwent surgery between 1988 and 2014 for MTC from five tertiary referral centres in The Netherlands were included. In total, primary tumours of 114 patients and lymph node metastases of 34 patients were analysed for expression of SSTR2A using a tissue microarray, and correlated with clinicopathological variables and survival.

RESULTS

The mean age of patients was 45.5 years (SD 16.2), 55 patients were male (49.5%). Primary tumours of 58 patients (50.9%) showed SSTR2A expression. In multivariate Cox-regression analysis, SSTR2A positivity correlated independently with better overall survival (OS) (HR 0.3; 95% CI 0.1-1.0). In stage IV MTC patients, 10-year survival rates for SSTR2A-negative and positive patients were 43% and 96%, respectively. In 53.9% of patients with lymph node metastases, expression in primary tumour and lymph node metastases differed.

CONCLUSION

SSTR2A expression is correlated with longer OS in MTC, especially for stage IV patients, suggesting that SSTR2A expression might be a useful prognostic factor in MTC. The SSTR2A status of the primary MTC does not predict expression in lymph node metastases.

Recent advances in the biology and therapy of medullary thyroid carcinoma

Medullary thyroid cancer (MTC) is a relatively uncommon yet prognostically significant thyroid cancer. Several recent advances in the biology and current or potential treatment of MTC are notable. These include a new understanding of the developmental biology of the thyroid C cell, which heretofore was thought to develop from the neural crest. RET, encoded by the most common driver gene in MTC, has been shown to be a dual function kinase, thus expanding its potential substrate repertoire. Promising new therapeutic developments are occurring; many have recently progressed to clinical development. There are new insights into RET inhibitor therapy for MTC. New strategies are being developed to inhibit the RAS proteins, which are potential therapeutic targets in MTC. Potential emerging immunotherapies for MTC are discussed. However, gaps in our knowledge of the basic biology of the C cell, its transformation to MTC, and the mechanisms of resistance to therapy impede progress; further research in these areas would have a substantial impact on the field.

Lu-177-Based Peptide Receptor Radionuclide Therapy for Advanced Neuroendocrine Tumors

Peptide receptor radionuclide therapy (PRRT) is a systemic cytotoxic radiation therapy using a compound of β-emitting radionuclide chelated to a peptide for the treatment of tumor with overexpressed specific cell receptor such as somatostatin receptor subtype 2 (SSTR2) of neuroendocrine tumor (NET). Surgical resection should be performed for the curative treatment for NETs when it is feasible; however, a multi-disciplinary approach is needed when locally advanced or metastasized disease. PRRT with lutetium-177 (Lu-177)-labeled somatostatin analogues, as a new treatment modality targeting metastatic or inoperable NETs expressing the SSTR2, have been developed and successfully used for the past two decades. As Lu-177 emits both β- and γ-radiation, it has the ability as a theragnostic agent for NETs compared with only β-emitting yttrium-90 labeled PRRT. Several recent studies reported that Lu-177 gave an overall positive response and improved the patients' quality of life. To fully exploit its potential, large comparative studies are needed for the assessment of distinct efficacies of Lu-177 labeled PRRT. Additionally, for extending the indications and developing new regimens of Lu-177-based PRRT, more dedicated clinical research is required.

The role of peptide receptor radionuclide therapy in advanced/metastatic thoracic neuroendocrine tumors

Bronchopulmonary (BP) neuroendocrine tumors (NETs) comprise a spectrum of tumors that develop from respiratory neuroendocrine cells and represent ~20% of all lung neoplasia and ~30% of all NETs. The only curative treatment is surgical resection. For well-differentiated forms (typical and atypical carcinoids), medical therapy ranges from bioactive agents (e.g., somatostatin analogs), to biotherapy (e.g., everolimus), standard chemotherapy and peptide receptor radionuclide therapy (PRRT). PRRT with radiolabeled somatostatin analogs is an innovative treatment for inoperable or metastasized, well/moderately differentiated, NET. Initially developed for gastroenteropancreatic tumors, it is also used in BP-NET because these tumors express the target receptor. Two decades of clinical trials with either ⁹⁰Y-octreotide or ¹⁷⁷Lu-octreotate, have demonstrated the efficacy of PRRT, as measured by tumor response, symptom relief and quality of life (QoL) improvement. PRRT with ⁹⁰Y- and ¹⁷⁷Lu-peptides is generally well-tolerated and adverse events (kidney and bone marrow) are modest. The paper illustrates the history, technique and results of this treatment in the few dedicated studies and the many BP NET cases embedded within larger NET series. The limitations of the present body of information are addressed, and the future perspectives, in terms of prospective studies required to define the position of PRRT in the therapeutic algorithm of BP-NETs and the need for predictive molecular biomarkers to guide future studies, are discussed.

Theranostics of Neuroendocrine Tumors

Somatostatin receptor positron emission tomography/computed tomography using ⁶⁸Ga-labeled somatostatin analogs is the mainstay for the evaluation of receptor status in neuroendocrine tumors (NETs). This translates towards better therapy options, with increasing evidence of peptide receptor radionuclide therapy (PRRT) as the treatment of choice for advanced or progressive NETs. There are benefits in progression-free and overall survival as well as a significant improvement in clinical condition. In patients with progressive NETs, fractionated, personalized PRRT results in good therapeutic responses with no significant severe hematological and/or renal toxicity, thus improving quality of life.

Medullary Thyroid Carcinoma

Medullary thyroid carcinoma (MTC) is subdivided into sporadic (75%) and hereditary (25%) forms. Several germline mutations in the RET proto-oncogene are the source of distinct clinical phenotypes in hereditary MTC including familial MTC (FMTC) and multiple endocrine neoplasia 2A (MEN 2A) and 2B (MEN 2B). The higher the penetrance of the MEN 2 phenotype the earlier the progression of MTC which forms the basis for the currently recommended codon-related concept of prophylactic thyroidectomy. In patients with sporadic MTC, routine calcitonin (CT) measurement in nodular goiter patients has been shown to reduce the frequency of advanced tumor stages. Patients with CT levels over 100 pg/ml after pentagastrin stimulation are recommended for total thyroidectomy. In patients with unexpected sporadic MTC after histological examination, completion thyroidectomy is currently only recommended when CT levels remain elevated. The extent of lymph node dissection in patients with MTC is controversial. However, with respect to lymphonodal micrometastases, systematic compartment-oriented microdissection has been shown to reduce the frequency of lymphonodal recurrence. On the other hand, to avoid unnecessary lymph node dissection, a more individualized concept is required in the future. New chemotherapeutic agents (tyrosine kinase inhibitors), therapeutic nuclids (90Yttrium-labeled octreotide), and chemoembolization of liver metastases are currently the most promising therapeutical concepts in patients with distant metastases.

Human Anti-Oxidation Protein A1M--A Potential Kidney Protection Agent in Peptide Receptor Radionuclide Therapy

Peptide receptor radionuclide therapy (PRRT) has been in clinical use for 15 years to treat metastatic neuroendocrine tumors. PRRT is limited by reabsorption and retention of the administered radiolabeled somatostatin analogues in the proximal tubule. Consequently, it is essential to develop and employ methods to protect the kidneys during PRRT. Today, infusion of positively charged amino acids is the standard method of kidney protection. Other methods, such as administration of amifostine, are still under evaluation and show promising results. α₁-microglobulin (A1M) is a reductase and radical scavenging protein ubiquitously present in plasma and extravascular tissue. Human A1M has antioxidation properties and has been shown to prevent radiation-induced in vitro cell damage and protect non-irradiated surrounding cells. It has recently been shown in mice that exogenously infused A1M and the somatostatin analogue octreotide are co-localized in proximal tubules of the kidney after intravenous infusion. In this review we describe the current situation of kidney protection during PRRT, discuss the necessity and implications of more precise dosimetry and present A1M as a new, potential candidate for renal protection during PRRT and related targeted radionuclide therapies.

Nuclear Medicine in Thyroid Diseases in Pediatric and Adolescent Patients

Both benign and malignant diseases of the thyroid are rare in the pediatric and adolescent population, except congenital hypothyroidism. Nuclear medicine plays a major role, both in the diagnosis and therapy of thyroid pathologies. Use of radioactivity in pediatric population is strictly controlled due to possible side effects such as secondary cancers; therefore, management of pediatric patients requires detailed literature knowledge. This article aims to overview current algorithms in the management of thyroid diseases and use of radionuclide therapy in pediatric and adolescent population.

Medullary Thyroid Carcinoma: Imaging

Imaging plays an important role in early detection and staging of medullary thyroid carcinoma (MTC) as well as in follow-up to localize early recurrence. MTC is a rare, calcitonin-secreting thyroid malignancy often diagnosed by ultrasound and calcitonin screening as part of the routine workup for any thyroid nodule. If calcitonin is elevated, imaging studies are needed for preoperative staging, which dictates surgical management. This can be done by ultrasound of the neck and abdomen. Computed tomography (CT) or magnetic resonance imaging (MRI) studies for more distant disease are done preoperatively if calcitonin levels are higher than 500 pg/ml. Neither FDG-PET/CT nor F-DOPA-PET/CT are used routinely for preoperative staging but may contribute in doubtful individual cases. Postoperative elevated calcitonin is related to persistence or recurrence of MTC. Imaging studies to localize tumor tissue during postoperative follow-up include ultrasound, CT, MRI as well as PET studies. They should be used wisely, however, since treatment consequences are often limited, and even patients with persistent disease may survive long enough to accumulate significant radiation doses. Imaging studies are also useful for diagnosis of associated components of the hereditary MTC such as pheochromocytoma and primary hyperparathyroidism (pHPT).

Prognostic value of positron emission tomography-assessed tumor heterogeneity in patients with thyroid cancer undergoing treatment with radiopeptide therapy

INTRODUCTION

Peptide receptor radionuclide therapy (PRRT) is a treatment option for both iodine-refractory differentiated and advanced medullary thyroid cancer (TC). It requires over-expression of somatostatin receptor subtype II (SSTR) that can be non-invasively assessed by positron emission tomography (PET). Assessment of tumor heterogeneity is increasingly used as a tool for prognostication prediction. We investigated the potential of SSTR-PET to assess intraindividual tumor heterogeneity and thereby treatment response prior to PRRT.

METHODS

12 patients with progressive radioiodine-refractory differentiated (1 papillary, 1 oxyphilic, 2 oncocytic, 4 follicular) or medullary (n=4) TC were enrolled. SSTR-PET was performed at baseline. Conventional PET parameters and heterogeneity parameters were analyzed regarding their potential to predict progression-free (PFS, mean, 221 days) and overall survival (OS, mean, 450 days). Parameters of a subgroup of lesions (n=23) were also correlated with morphological response according to modified RECIST criteria.

RESULTS

In patient-based analysis, all conventional parameters failed to predict PFS. Several textural parameters showed a significant capability to assess PFS. Thereby, "Grey level non uniformity" had the highest area under the curve (AUC, 0.93) in Receiver operating characteristics analysis followed by "Contrast" (AUC, 0.89). In lesion-based analysis, only "Entropy" revealed potential to evaluate disease progression. OS could not be assessed by any parameter investigated.

CONCLUSIONS

Tumor heterogeneity seems to be a predictor of response to PRRT in patients with iodine-refractory differentiated/advanced medullary thyroid cancer and outperforms conventional PET parameters like standardized uptake value. In a "theranostic" approach, assessment of textural parameters may help in selecting patients who might benefit from PRRT.

Diagnóstico, tratamento e seguimento do carcinoma medular de tireoide: recomendações do Departamento de Tireoide da Sociedade Brasileira de Endocrinologia e Metabologia

Introdução O carcinoma medular de tireoide (CMT) origina-se das células parafoliculares da tireoide e corresponde a 3-4% das neoplasias malignas da glândula. Aproximadamente 25% dos casos de CMT são hereditários e decorrentes de mutações ativadoras no proto-oncogene RET (REarranged during Transfection). O CMT é uma neoplasia de curso indolente, com taxas de sobrevida dependentes do estádio tumoral ao diagnóstico. Este artigo descreve diretrizes baseadas em evidências clínicas para o diagnóstico, tratamento e seguimento do CMT. Objetivo O presente consenso, elaborado por especialistas brasileiros e patrocinado pelo Departamento de Tireoide da Sociedade Brasileira de Endocrinologia e Metabologia, visa abordar o diagnóstico, tratamento e seguimento dos pacientes com CMT, de acordo com as evidências mais recentes da literatura. Materiais e métodos: Após estruturação das questões clínicas, foi realizada busca das evidências disponíveis na literatura, inicialmente na base de dados do MedLine-PubMed e posteriormente nas bases Embase e SciELO – Lilacs. A força das evidências, avaliada pelo sistema de classificação de Oxford, foi estabelecida a partir do desenho de estudo utilizado, considerando-se a melhor evidência disponível para cada questão. Resultados Foram definidas 11 questões sobre o diagnóstico, 8 sobre o tratamento cirúrgico e 13 questões abordando o seguimento do CMT, totalizando 32 recomendações. Como um todo, o artigo aborda o diagnóstico clínico e molecular, o tratamento cirúrgico inicial, o manejo pós-operatório e as opções terapêuticas para a doença metastática. Conclusões O diagnóstico de CMT deve ser suspeitado na presença de nódulo tireoidiano e história familiar de CMT e/ou associação com feocromocitoma, hiperparatireoidismo e/ou fenótipo sindrômico característico, como ganglioneuromatose e habitus marfanoides. A punção aspirativa por agulha fina do nódulo, a dosagem de calcitonina sérica e o exame anatomopatológico podem contribuir na confirmação do diagnóstico. A cirurgia é o único tratamento que oferece a possibilidade de cura. As opções de tratamento da doença metastática ainda são limitadas e restritas ao controle da doença. Uma avaliação pós-cirúrgica criteriosa para a identificação de doença residual ou recorrente é fundamental para definir o seguimento e a conduta terapêutica subsequente.

Medical management of metastatic medullary thyroid cancer

Medullary thyroid cancer (MTC) is an aggressive form of thyroid cancer that occurs in both heritable and sporadic forms. Discovery that mutations in the rearranged during transfection (RET) proto-oncogene predispose to familial cases of this disease has allowed for presymptomatic identification of gene carriers and prophylactic surgery to improve the prognosis of these patients. A significant number of patients with the sporadic type of MTC and even those with familial disease still present with lymph node or distant metastases, making surgical cure difficult. Over the past several decades, many different types of therapy for metastatic disease have been attempted with limited success. Improved understanding of the molecular defects and pathways involved in both familial and sporadic MTC has resulted in new hope for these patients with the development of drugs targeting the specific alterations responsible. This new era of targeted therapy with kinase inhibitors represents a significant step forward from previous trials of chemotherapy, radiotherapy, and hormone therapy. Although much progress has been made, additional agents and strategies are needed to achieve durable, long-term responses in patients with metastatic MTC. This article reviews the history and results of medical management for metastatic MTC from the early 1970s up until the present day.

Comparison of different positron emission tomography tracers in patients with recurrent medullary thyroid carcinoma: our experience and a review of the literature

Several morphological and functional imaging techniques are usually used to detect residual/recurrent medullary thyroid carcinoma (MTC) with variable results; currently, there is growing interest in positron emission tomography (PET) methodology. Herein, we report our experience of and a literature review about the comparison of different positron emission tomography (PET) tracers in patients with residual/recurrent MTC. (18)F-DOPA PET/CT seems to be the most useful imaging method to detect recurrent MTC lesions, performing better than (18)F-FDG and (68)Ga-somatostatin analogs PET/CT. (18)F-FDG may complement (18)F-DOPA in patients with aggressive tumors. (68)Ga-somatostatin analogs PET/CT may be useful to select patients who could benefit from radioreceptor therapy. The information provided by the various PET tracers reflects different metabolic pathways, and may help to select the most appropriate treatment.

The joint IAEA, EANM, and SNMMI practical guidance on peptide receptor radionuclide therapy (PRRNT) in neuroendocrine tumours

Peptide receptor radionuclide therapy (PRRNT) is a molecularly targeted radiation therapy involving the systemic administration of a radiolabelled peptide designed to target with high affinity and specificity receptors overexpressed on tumours. PRRNT employing the radiotagged somatostatin receptor agonists (90)Y-DOTATOC ([(90)Y-DOTA(0),Tyr(3)]-octreotide) or (177)Lu-DOTATATE ([(177)Lu-DOTA(0),Tyr(3),Thr(8)]-octreotide or [(177)Lu-DOTA(0),Tyr(3)]-octreotate) have been successfully used for the past 15 years to target metastatic or inoperable neuroendocrine tumours expressing the somatostatin receptor subtype 2. Accumulated evidence from clinical experience indicates that these tumours can be subjected to a high absorbed dose which leads to partial or complete objective responses in up to 30 % of treated patients. Survival analyses indicate that patients presenting with high tumour receptor expression at study entry and receiving (177)Lu-DOTATATE or (90)Y-DOTATOC treatment show significantly higher objective responses, leading to longer survival and improved quality of life. Side effects of PRRNT are typically seen in the kidneys and bone marrow. These, however, are usually mild provided adequate protective measures are undertaken. Despite the large body of evidence regarding efficacy and clinical safety, PRRNT is still considered an investigational treatment and its implementation must comply with national legislation, and ethical guidelines concerning human therapeutic investigations. This guidance was formulated based on recent literature and leading experts' opinions. It covers the rationale, indications and contraindications for PRRNT, assessment of treatment response and patient follow-up. This document is aimed at guiding nuclear medicine specialists in selecting likely candidates to receive PRRNT and to deliver the treatment in a safe and effective manner. This document is largely based on the book published through a joint international effort under the auspices of the Nuclear Medicine Section of the International Atomic Energy Agency.

Yttrium-labelled peptides for therapy of NET

Peptide receptor radionuclide therapy (PRRT) consists in the systemic administration of a synthetic peptide, labelled with a suitable beta-emitting radionuclide, able to irradiate tumours and their metastases via the internalization through a specific receptor, overexpressed on the cell membrane. After 15 years of experience, we can state that PRRT with (90)Y-labelled peptides is generally well tolerated. Acute side effects are usually mild, some of which are related to the co-administration of amino acids, such as nausea. Others are related to the radiopeptide, such as fatigue or the exacerbation of an endocrine syndrome, which rarely occurs in functioning tumours. Chronic and permanent effects on target organs, particularly the kidneys and the bone marrow, are generally mild if the necessary precautions are taken. Currently, the potential risk to kidney and red marrow limits the amount of radioactivity that may be administered. However, when tumour masses are irradiated with adequate doses, volume reduction may be observed. (90)Y-octreotide has been the most widely used radiopeptide in the first 8-10 years of experience. Unfortunately, all of the published results derive from different and inhomogeneous phase I/II studies. Hence, a direct comparison is virtually impossible to date. Nevertheless, even with these limitations, objective responses are registered in 10-34% of patients. The optimal timing of (90)Y-DOTATOC in the management of somatostatin receptor (SSTR)-positive tumours and the way in which it should be integrated with other treatments have yet to be defined, and prospective phase II/III trials comparing the efficacy and toxicity of different schemes of (90)Y-DOTATOC administration are still warranted.

Advances in the follow-up of differentiated or medullary thyroid cancer

The long-term survival of patients with thyroid cancer and the possibility of tumour recurrence up to 30-40 years after the achievement of a disease-free status illustrate the importance of lifelong follow-up in these individuals. This Review discusses the most innovative aspects of follow-up protocols for patients with differentiated thyroid cancer, that is, of papillary or follicular hystotype, and those with medullary thyroid cancer. Particular focus is placed on the relevance of new ultrasensitive assays for thyroglobulin measurement and the option of using recombinant human TSH to stimulate thyroglobulin secretion. Methods to compensate for the loss of diagnostic significance of serum thyroglobulin levels in patients with differentiated thyroid cancer and circulating anti-thyroglobulin antibodies are highlighted, as well as the role of the postoperative calcitonin stimulation test and the clinical relevance of determining the doubling time of calcitonin and carcinoembryonic antigen in patients with medullary thyroid cancer. Moreover, this Review gives some insights into the role of molecular thyroid cancer testing, both for prognostic and for therapeutic purposes. Finally, a general overview of traditional imaging procedures, such as neck ultrasonography, CT, MRI and bone scintigraphy, is provided alongside a comparison with new nuclear imaging tests such as PET.

Targeted systemic radiotherapy of pheochromocytoma and medullary thyroid cancer

Targeted systemic radiotherapy constitutes the systemic administration of a radioactive agent that targets a molecule expressed preferentially on cancer cells. The archetypal such therapy is 131-iodine ((131)I) therapy for differentiated thyroid cancers. Radiotherapy typically delivers a calculated radiation-absorbed dose to tumor that takes into account (contiguous) normal tissue. Systemic radiotherapy development currently uses schema more analogous to chemotherapy--a radioactivity estimate that does not cause any irreversible toxicity. Historically, arbitrary amounts of radioactivity shown to be effective, on the basis of retrospective review, were used for thyroid cancer therapy with (131)I as well as for neuroendocrine tumor therapy with (131)I-labeled meta-iodo-benzylguanidine (MIBG). Their established safety record has led to adaptations that include repeat therapies with nontoxic amounts of radioactivity. There remains, however, a lack of clear understanding of the safety limits of systemic targeted radiotherapy. This is probably most true in systemic therapy with MIBG in adult neuroendocrine tumors. Bone marrow is the primary critical organ for most targeted systemic radiotherapy; second organ involvement may be renal, as with MIBG and targeted radiopeptide therapy, or pulmonary, as with radioimmunotherapy. Most therapies have tended toward multiple administrations of subtoxic amounts of radioactivity. Therapy with MIBG in pheochromococytoma as well as targeted radiopeptide therapy in medullary thyroid cancer has followed this model. Radioimmunotherapy appears very promising; a definitive Phase 2 study needs completion. All therapy has shown promise in extending disease survival (as compared with historical controls), with few major structural (or biochemical) responses. This review will attempt to compliment the excellent existing literature by providing an overall systemic therapeutic approach to this promising endeavor.

Comparison of 18F-DOPA, 18F-FDG and 68Ga-somatostatin analogue PET/CT in patients with recurrent medullary thyroid carcinoma

PURPOSE

To retrospectively evaluate and compare (18)F-FDG, (18)F-DOPA and (68)Ga-somatostatin analogues for PET/CT in patients with residual/recurrent medullary thyroid carcinoma (MTC) suspected on the basis of elevated serum calcitonin levels.

METHODS

Included in the study were 18 patients with recurrent MTC in whom functional imaging with the three tracers was performed. The PET/CT results were compared on a per-patient basis and on a per-lesion-basis.

RESULTS

At least one focus of abnormal uptake was observed on PET/CT in 13 patients with (18)F-DOPA (72.2% sensitivity), in 6 patients with (68)Ga-somatostatin analogues (33.3%) and in 3 patients with (18)F-FDG (16.7%) (p < 0.01). There was a statistically significant difference in sensitivity between (18)F-DOPA and (18)F-FDG PET/CT (p < 0.01) and between (18)F-DOPA and (68)Ga-somatostatin analogue PET/CT (p = 0.04). Overall, 72 lesions were identified on PET/CT with the three tracers. (18)F-DOPA PET/CT detected 85% of lesions (61 of 72), (68)Ga-somatostatin analogue PET/CT 20% (14 of 72) and (18)F-FDG PET/CT 28% (20 of 72). There was a statistically significant difference in the number of lymph node, liver and bone lesions detected with the three tracers (p < 0.01). In particular, post-hoc tests showed a significant difference in the number of lymph node, liver and bone lesions detected by (18)F-DOPA PET/CT and (18)F-FDG PET/CT (p < 0.01 for all the analyses) and by (18)F-DOPA PET/CT and (68)Ga-somatostatin analogue PET/CT (p < 0.01 for all the analyses). The PET/CT results led to a change in management of eight patients (44%).

CONCLUSION

(18)F-DOPA PET/CT seems to be the most useful imaging method for detecting recurrent MTC lesions in patients with elevated serum calcitonin levels, performing better than (18)F-FDG and (68)Ga-somatostatin analogue PET/CT. (18)F-FDG may complement (18)F-DOPA in patients with an aggressive tumour.

New treatment modalities in advanced thyroid cancer

BACKGROUND

Thyroid cancer is a heterogeneous disease that is classified into differentiated thyroid carcinoma (DTC), undifferentiated/anaplastic thyroid carcinoma (ATC) and medullary thyroid carcinoma. Results of conventional treatment modalities in advanced thyroid cancer have been disappointing and therefore, new therapies are needed.

METHODS

We searched PubMed, The Cochrane Library, Medline and EMBASE databases and abstracts published in annual proceedings for new treatment modalities in advanced thyroid cancer. We also searched for ongoing trials in www.clinicaltrials.gov.

RESULTS

Six phase I, 17 phase II and 1 phase III trials with tyrosine kinase inhibitors were carried out. We found 2 pilot studies and 11 phase II trials with redifferentiation therapies, mainly in DTC. For antiproliferative approaches, three phase I and four phase II trials were found. Immunomodulatory gene therapy was tested in a pilot study in ATC patients. Two phase II trials were carried out with immunotherapy. One phase I and nine phase II trials were found with radionucleotide therapy in patients with DTC.

CONCLUSION

The developments in the treatment of advanced thyroid cancer are intriguing. Future trials should aim at combinations of targeted agents with or without other treatment modalities, and will hopefully contribute to further improvement of outcomes.

Targeted radiotherapy with radiolabeled somatostatin analogs

Targeted radiopeptide therapy with (90)Yttrium- or (177)Lutetium-labeled somatostatin analogs has been proven to improve significantly quality of life and survival in patients suffering from metastatic or unresectable neuroendocrine tumors (NETs). Roughly 25% of patients achieve partial remission; progression-free survival is estimated to be 30 to 40 months. A wide range of protocols using different somatostatin analogs, isotopes, injected activity per cycle of administration, and number of cycles are reported. More patient-based therapy protocols are under development, taking into consideration the complexity of NET cell biology, dosimetric issues, and the availability of different radiolabeled analogs. This article reviews the effectiveness and safety of the different protocols and discusses several clinical algorithms used in an attempt to optimize targeted radiopeptide therapy.

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.

Comparison of (68)Ga-DOTATATE and (18)F-fluorodeoxyglucose PET/CT in the detection of recurrent medullary thyroid carcinoma

PURPOSE

This was a retrospective study to detect and map the extent of disease in recurrent medullary thyroid carcinoma (MTC) using the novel PET somatostatin analogue (68)Ga-DOTATATE and conventional (18)F-FDG positron emission tomography/computed tomography (PET/CT).

METHODS

Eighteen patients (13 men, 5 women, median age: 54 years) who had previously been operated on for MTC and presented with biochemical (raised calcitonin levels) and/or imaging evidence of recurrence underwent both (68)Ga-DOTATATE and (18)F-FDG PET/CT within a maximum interval of 4 weeks (median interval of 1 week). (68)Ga-DOTATATE- and (18)F-FDG-avid lesions were recorded per patient as well as per region in six distinct regions: (1) thyroid bed-local recurrence, (2) cervical lymph nodes, (3) mediastinum, (4) lungs, (5) liver and (6) bones. The (68)Ga-DOTATATE and (18)F-FDG PET/CT findings were classified as positive or negative on visual interpretation. These findings were further characterised as concordant or discordant, depending on whether there was agreement or discrepancy in imaging with the two radiotracers. A separate analysis of the unenhanced CT component of the examination was performed. Verification of the lesions was achieved by histopathological analysis, further imaging studies and clinical follow-up.

RESULTS

(68)Ga-DOTATATE PET/CT imaging achieved disease detection in 13 of 18 and (18)F-FDG PET/CT in 14 of 18 patients. These results corresponded to per-patient sensitivities of 72.2% [95% confidence interval (CI): 46.4-89.3%] for (68)Ga-DOTATATE versus 77.8% (95% CI: 51.9-92.6%) for (18)F-FDG (non-significant difference). (18)F-FDG revealed a total of 28 metastatic MTC regions and (68)Ga-DOTATATE 23 regions. In ten patients a discordant tracer pattern of per-region and/or per-lesion distribution of recurrent disease was observed, while in four patients a concordant pattern was noted (no lesions were detected by either modality in the remaining four patients).

CONCLUSION

Neither (18)F-FDG nor (68)Ga-DOTATATE PET/CT can fully map the extent of disease in patients with recurrent MTC, although (18)F-FDG PET/CT may identify more lesions. However, (68)Ga-DOTATATE PET/CT can be a useful complementary imaging tool and may identify patients suitable for consideration of targeted radionuclide somatostatin analogue therapy.

Multiple endocrine neoplasia type 2

Multiple endocrine neoplasia type 2 (MEN 2) is an autosomal dominantly inherited tumor syndrome subclassified into three distinct syndromes: MEN 2A, MEN 2B and familial medullary thyroid carcinoma. In MEN 2 families, medullary thyroid carcinoma, pheochromocytomas and parathyroid adenomas occur with a variable frequency, also depending on the specific genetic defect involved. In 1993, the responsible MEN2 gene was identified. The genetic defect in these disorders involves the RET proto-oncogene on chromosome 10. The germline RET mutations result in a gain-of-function of the RET protein. Extensive studies on large families revealed that there is a strong genotype-phenotype correlation. In this review, guidelines for early diagnosis, including MEN2 gene mutation analysis, and treatment, including preventive surgery, periodic and clinical monitoring, have been formulated, enabling improvement of life expectancy and quality of life. Identification of the RET protein has also provided new insights into its function, and the specific pathways it effects involved in cell proliferation, migration, differentiation and survival. In the near future, identification of biological tumor markers will enable target-directed intervention and may prevent and/or delay progression of both primary and residual tumor growth.

Medullary thyroid carcinoma and biomarkers: past, present and future

The clinical management of patients with persistent or recurrent medullary thyroid carcinoma (MTC) is still under debate, because these patients either have a long-term survival, due to an indolent course of the disease, or develop rapidly progressing disease leading to death from distant metastases. At this moment, it cannot be predicted what will happen within most individual cases. Biomarkers, indicators which can be measured objectively, can be helpful in MTC diagnosis, molecular imaging and treatment, and/or identification of MTC progression. Several MTC biomarkers are already implemented in the daily management of MTC patients. More research is being aimed at the improvement of molecular imaging techniques and the development of molecular systemic therapies. Recent discoveries, like the prognostic value of plasma calcitonin and carcino-embryonic antigen doubling-time and the presence of somatic RET mutations in MTC tissue, may be useful tools in clinical decision making in the future. In this review, we provide an overview of different MTC biomarkers and their applications in the clinical management of MTC patients.

Peptide receptor therapies in neuroendocrine tumors

Neuroendocrine tumors (NETs) are relatively rare tumors, mainly originating from the digestive system, able to produce bioactive amines and hormones. NETs tend to be slow growing and are often diagnosed when metastatic. The localization of a NETs and the assessment of the extent of disease are crucial for management. Commonly used diagnostic techniques include morphological imaging (ultrasound, computerized tomography, magnetic resonance), and functional imaging (somatostatin receptor scintigraphy, positron emission tomography techniques). Treatment is multidisciplinary and should be individualized according to the tumor type, burden, and symptoms. Therapeutic tools include surgery, interventional radiology, and medical treatments such as somatostatin analogues, interferon, chemotherapy, new targeted drugs and peptide receptor radionuclide therapy (PRRT) with radiolabeled somatostatin analogues. NETs usually over-express somatostatin receptors, thus enabling the therapeutic use of somatostatin analogues, one of the basic tools, able to reduce signs and symptoms of hormone hypersecretion, improve quality of life, and slow tumor growth. PRRT with somatostatin analogues 90Y-DOTATOC and 177Lu-DOTATATE has been explored in NETs for more than a decade. Present knowledge and clinical studies indicate that it is possible to deliver high-absorbed doses to tumors expressing sst2 receptors, with partial and complete objective responses in up to 30% of patients. Side effects, involving the kidney and the bone marrow, are mild if adequate renal protection is used. Moreover, a consistent survival benefit is reported. As NETs may also express cholecystokinin 2, bombesin, neuropeptide Y or vasoactive intestinal peptide receptors even simultaneously, the potential availability and biological stability of radio-analogues will improve the multireceptor targeting of NETs.