Treatment of neuroendocrine tumours in adults with 131I-MIBG therapy

Radio theranostics in paragangliomas and pheochromocytomas

This continuing education aims to present in a clear and easy-to-understand manner the biology of paragangliomas and pheochromocytomas (PPGLs), the functional imaging studies available for their diagnosis and therapeutic planning, the requirements necessary to administer radioligand therapy (RLT) and the characteristics of these treatments (inclusion criteria, administration protocols, adverse effects and future perspectives). In this pathology we have two RLT options: [131I]MIBG and [177Lu]Lu-DOTA-TATE. The indication for treatment is determined by the expression of its therapeutic target in functional imaging studies, allowing precision and personalized medicine. Although most of the results we have for both treatments have as origin small retrospective series, RLT is presented as a safe and well-tolerated therapeutic option in PPGLs with slow-moderate progression or with uncontrollable symptoms, obtaining high disease control rates.

Response to targeted radionuclide therapy with [131I]MIBG AND [177Lu]Lu-DOTA-TATE according to adrenal vs. extra-adrenal primary location in metastatic paragangliomas and pheochromocytomas: A systematic review

PURPOSE

Targeted radionuclide therapy (TRT) with [¹³¹I]MIBG and [¹⁷⁷Lu]Lu-DOTA-TATE is an alternative treatment to the classic schemes in slow progressive metastatic/inoperable paraganglioma (PGL) and pheochromocytoma (PHEO). There is no consensus on which treatment to administer and/or the best sequence in patients who are candidates for both therapies. To clarify these questions, this systematic review assesses the prognostic value of [¹³¹I]MIBG and ^[177Lu]Lu-DOTA-TATE (PRRT-Lu) treatments in terms of progression-free survival (PFS) both globally and considering the primary location.

METHODS

This review was developed according to the PRISMA Statement with 27 final studies (608 patients). Patient characteristics, treatment procedure, and follow-up criteria were evaluated. In addition, a Bayesian linear regression model weighted according to its sample size and an alternative model, which also included an interaction between the treatment and the proportion of PHEOs, were carried out, adjusted by a Student's t distribution.

RESULTS

In linear regression models, [¹³¹I]MIBG overall PFS was, on average, 10 months lower when compared with PRRT-Lu. When considering the interaction between treatment responses and the proportion of PHEOs, PRRT-Lu showed remarkably better results in adrenal location. The PFS of PRRT-Lu was longer when the ratio of PHEOs increased, with a decrease in [¹³¹I]MIBG PFS by 1.9 months for each 10% increase in the proportion of PHEOs in the sample.

CONCLUSION

Methodology, procedure, and PFS from the different studies are quite heterogeneous. PRRT-Lu showed better results globally and specifically in PHEOs. This fact opens the window to prospective trials comparing or sequencing [¹³¹I]MIBG and PRRT-Lu.

An open-label, single-arm, multi-center, phase II clinical trial of single-dose [131I]meta-iodobenzylguanidine therapy for patients with refractory pheochromocytoma and paraganglioma

OBJECTIVE

In this phase II study, we aimed to investigate the efficacy and safety of single-dose [¹³¹I]meta-iodobenzylguanidine (¹³¹I-mIBG) therapy in patients with refractory pheochromocytoma and paraganglioma (PPGL).

PATIENTS AND METHODS

This study was designed as an open-label, single-arm, multi-center, phase II clinical trial. The enrolled patients were administered 7.4 GBq of ¹³¹I-mIBG. Its efficacy was evaluated 12 and 24 weeks later, and its safety was monitored continuously until the end of the study. We evaluated the biochemical response rate as the primary endpoint using the one-sided exact binomial test based on the null hypothesis (≤ 5%).

RESULTS

Seventeen patients were enrolled in this study, of which 16 were treated. The biochemical response rate (≥ 50% decrease in urinary catecholamines) was 23.5% (90% confidence interval: 8.5-46.1%, p = 0.009). The radiographic response rates, determined with CT/MRI according to the response evaluation criteria in solid tumors (RECIST) version 1.1 and ¹²³I-mIBG scintigraphy were 5.9% (0.3%-25.0%) and 29.4% (12.4%-52.2%), respectively. The most frequent non-hematologic treatment-emergent adverse events (TEAEs) were gastrointestinal symptoms including nausea, appetite loss, and constipation, which were, together, observed in 15 of 16 patients. Hematologic TEAEs up to grade 3 were observed in 14 of 16 patients. No grade 4 or higher TEAEs were observed. All patients had experienced at least one TEAE, but no fatal or irreversible TEAEs were observed.

CONCLUSION

A single dose ¹³¹I-mIBG therapy was well tolerated by patients with PPGL, and statistically significantly reduced catecholamine levels compared to the threshold response rate, which may lead to an improved prognosis for these patients.

Addition of 131I-MIBG to PRRT (90Y-DOTATOC) for Personalized Treatment of Selected Patients with Neuroendocrine Tumors

Peptide receptor radionuclide therapy (PRRT) is an effective treatment for metastatic neuroendocrine tumors. Delivering a sufficient tumor radiation dose remains challenging because of critical-organ dose limitations. Adding ¹³¹I-metaiodobenzylguanidine (¹³¹I-MIBG) to PRRT may be advantageous in this regard. Methods: A phase 1 clinical trial was initiated for patients with nonoperable progressive neuroendocrine tumors using a combination of ⁹⁰Y-DOTATOC plus ¹³¹I-MIBG. Treatment cohorts were defined by radiation dose limits to the kidneys and the bone marrow. Subject-specific dosimetry was used to determine the administered activity levels. Results: The first cohort treated subjects to a dose limit of 1,900 cGy to the kidneys and 150 cGy to the marrow. No dose-limiting toxicities were observed. Tumor dosimetry estimates demonstrated an expected dose increase of 34%–83% using combination therapy as opposed to ⁹⁰Y-DOTATOC PRRT alone. Conclusion: These findings demonstrate the feasibility of using organ dose for a phase 1 escalation design and suggest the safety of using ⁹⁰Y-DOTATOC and ¹³¹I-MIBG.

Low-Dose, Low-Specific Activity 131I-metaiodobenzyl Guanidine Therapy in Metastatic Pheochromocytoma/Sympathetic Paraganglioma: Single-Center Experience from Western India

INTRODUCTION

Radionuclide therapy is a promising treatment modality in metastatic pheochromocytoma/paraganglioma (PPGL). There is scarce data on ¹³¹I-metaiodobenzyl guanidine (¹³¹I-MIBG) therapy from the Indian subcontinent. Hence, we aim to study the safety and effectiveness of low-dose, low-specific activity (LSA) ¹³¹I-MIBG therapy in patients with symptomatic, metastatic PPGL.

METHODS

Clinical, hormonal, and radiological response parameters and side effects of LSA ¹³¹I-MIBG therapy in patients with symptomatic, metastatic PPGL were retrospectively reviewed. World health organizations' (WHO) symptomatic, hormonal, and tumor response, and response evaluation criteria in solid tumors (RECIST1.1) criteria were used to assess the response.

RESULTS

Seventeen (PCC: 11, sympathetic PGL: 06) patients (15 with disease progression) received low-dose LSA ¹³¹I-MIBG therapy. Complete remission (CR), partial remission (PR), stable disease (SD), and progressive disease (PD) were 18% (3/17), 24% (4/17), 18% (3/17), and 41% (7/17), respectively, for WHO symptomatic response; 20% (2/10), 10% (1/10), 30% (3/10), and 40% (4/10), respectively, for WHO hormonal response; and 19% (3/16), 6% (1/16), 31% (5/16), and 44% (7/16), respectively for tumor response based on RECIST1.1. All patients with symptomatic PD and 50% (2/4) with hormonal PD had progression as per RECIST1.1 criteria. Side effects included thrombocytopenia, acute myeloid leukemia, mucoepidermoid carcinoma, and azoospermia in 6% (1/17) each.

CONCLUSIONS

Our study reaffirms the modest efficacy and safety of low-dose, LSA ¹³¹I-MIBG therapy in patients with symptomatic, metastatic PPGL. Symptomatic, but not hormonal, progression after ¹³¹I-MIBG therapy correlates well with tumor progression and should be further evaluated with imaging. In resource-limited settings, anatomic imaging alone may be used to assess tumor response to ¹³¹I-MIBG therapy.

Theranostics: Leveraging Molecular Imaging and Therapy to Impact Patient Management and Secure the Future of Nuclear Medicine

Nuclear medicine is experiencing a renaissance, with U.S. Food and Drug Administration approval recently being obtained for theranostic agents and a wide variety of such agents soon to impact patient care significantly in the era of precision medicine. The NETTER-1 trial demonstrated the therapeutic effect of a theranostic agent in markedly improving progression-free survival in patients with metastatic gastroenteropancreatic neuroendocrine tumors. Predominantly retrospective studies have demonstrated a significant response to ¹⁷⁷Lu-labeled agents targeting prostate-specific membrane antigen (PSMA) in patients with prostate cancer. At least 2 prospective clinical trials involving ¹⁷⁷Lu-PSMA agents are under way that will likely pave the way for Food and Drug Administration approval in the United States. A significant upside to theranostics is that patients tend to tolerate these agents better than chemotherapy. Theranostic compounds are likely to impact many cancers in the near future, not only through improvements in quality of life but also in terms of survival. This article provides an overview of already approved agents as well as those on the horizon. It is important that as these agents are clinically onboarded, nuclear medicine physicians have the expertise to deploy theranostics safely and efficiently, ensuring that these agents attain and maintain their position as leading lines of therapy in managing patients with cancer as well as becoming an important aspect of nuclear medicine practice in the future.

Molecular Imaging and Therapy for Neuroendocrine Tumors

OPINION STATEMENT

Neuroendocrine tumors (NETs) are relatively rare, with 12,000-15,000 new cases diagnosed annually in the USA. Although NETs are a diverse group of neoplasms, they share common molecular targets that can be exploited using nuclear medicine techniques for both imaging and therapy. NETs have traditionally been imaged with SPECT imaging using ¹¹¹In-labeled octreotide analogs to detect neoplasms with somatostatin receptors. In addition, certain NETs (pheochromocytomas, paragangliomas, and neuroblastomas) are also effectively imaged using ¹²³I- or ¹³¹I-labeled metaiodobenzylguanidine (MIBG), an analog of guanethidine. More recently, PET imaging with ⁶⁸Ga-labeled somatostatin receptor (SSR) analogs allows neuroendocrine tumors to be imaged with much higher sensitivity. ⁶⁸Ga-DOTATATE was approved as a PET tracer by the FDA in June 2016. In addition to imaging, both MIBG and DOTATATE can be labeled with therapeutic radionuclides to deliver targeted radiation selectively to macroscopic and microscopic tumor sites. The incorporation of the same molecular probe for imaging and therapy provides a radio-theranostic approach to identifying, targeting, and treating tumors. Over the years, several centers have experience treating NETs with high-dose ¹³¹I-MIBG. ¹⁷⁷Lu-DOTATATE was approved by the FDA in 2018 for treatment of gastroenteropancreatic NETs and constitutes a major advancement in the treatment of these diseases. In this paper, we provide an overview of imaging and treating neuroendocrine tumors using MIBG and SSR probes. Although uncommon, neuroendocrine tumors have provided the largest experience for targeted radionuclide imaging and therapy (with the exception of radioiodine treatment for thyroid disease). In addition to benefitting patients with these rare tumors, the knowledge gained provides a blueprint for the development of future paired diagnostic/therapeutic probes for treating other diseases, such as prostate cancer.

Predictors of Survival in 211 Patients with Stage IV Pulmonary and Gastroenteropancreatic MIBG-Positive Neuroendocrine Tumors Treated with 131I-MIBG

This retrospective analysis identifies predictors of survival in a cohort of patients with meta-iodobenzylguanidine (MIBG)-positive stage IV pulmonary and gastroenteropancreatic neuroendocrine tumor (P/GEP-NET) treated with ¹³¹I-MIBG therapy, to inform treatment selection and posttreatment monitoring. Methods: Survival, symptoms, imaging, and biochemical response were extracted via chart review from 211 P/GEP-NET patients treated with ¹³¹I-MIBG between 1991 and 2014. For patients with CT follow-up (n = 125), imaging response was assessed by RECIST 1.1 if images were available (n = 76) or by chart review of the radiology report if images could not be reviewed (n = 49). Kaplan-Meier analysis and Cox multivariate regression estimated survival and progression-free survival benefits predicted by initial imaging, biochemical response, and symptomatic response. Results: All patients had stage IV disease at the time of treatment. Median survival was 29 mo from the time of treatment. Symptomatic response was seen in 71% of patients, with the median duration of symptomatic relief being 12 mo. Symptomatic response at the first follow-up predicted a survival benefit of 30 mo (P < 0.001). Biochemical response at the first clinical follow-up was seen in 34% of patients, with stability of laboratory values in 48%; response/stability versus progression extended survival by 40 mo (P < 0.03). Imaging response (20% of patients) or stability (60%) at the initial 3-mo follow-up imaging extended survival by 32 mo (P < 0.001). Additionally, multiple ¹³¹I-MIBG treatments were associated with 24 mo of additional survival (P < 0.05). Conclusion: Therapeutic ¹³¹I-MIBG for metastatic P/GEP-NETs appears to be an effective means of symptom palliation. Imaging, biochemical, and symptomatic follow-up help prognosticate expected survival after ¹³¹I-MIBG therapy. Multiple rounds of ¹³¹I-MIBG are associated with prolonged survival.

Paradigm shift in theranostics of neuroendocrine tumors: conceptual horizons of nanotechnology in nuclear medicine

We present a comprehensive review of Neuroendocrine Tumors (NET) and the current and developing imaging and therapeutic modalities for NET with emphasis on Nuclear Medicine modalities. Subsequently, nanotechnology and its emerging role in cancer management, especially NET, are discussed. The article is both educative and informative. The objective is to provide an insight into the developments made in nuclear medicine and nanotechnology towards management of NET, individually as well as combined together.

I-131 Metaiodobenzylguanidine Therapy of Pheochromocytoma and Paraganglioma

Pheochromocytomas and paragangliomas are rare tumors arising from chromaffin cells. Available therapeutic modalities consist of chemotherapy, tyrosine kinase inhibitors, and I-131 metaiodobenzylguanidine (MIBG). I-131 MIBG is taken up via specific receptors and localizes into many but not all pheochromocytomas and paragangliomas. Because these tumors are rare, most therapy studies are retrospective presentations of clinical experience. Numerous retrospective studies and a few prospective studies have shown favorable responses in this disease, including symptomatic, biochemical, and objective responses. In this report, we review the experience of using I-131 MIBG therapy for targeting pheochromocytoma and paragangliomas.

Treatment of symptomatic neuroendocrine tumor syndromes: recent advances and controversies

INTRODUCTION

Neuroendocrine tumors(NETs), once thought rare, are increasing in frequency in most countries and receiving increasing-attention. NETs present two-treatment problems. A proportion is aggressive and a proportion has a functional, hormone-excess-state(F-NET), each of which must be treated. Recently, there have been many advances, well-covered in reviews/consensus papers on imaging-NETs; new, novel anti-tumor treatments and understanding their pathogenesis. However, little attention has been paid to advances in the treatment of the hormone-excess-state. These advances are usually reported in case-series, and case-reports with few large studies. In this paper these advances are reviewed. Areas covered: Advances in the last 5-years are concentrated on, but a review of literature from the last 10-years was performed. PubMed and other databases (Cochrane, etc.) were searched for F-NET-syndromes including carcinoid-syndrome, as well as meeting-abstracts on NETs. All advances that controlled hormone-excess-states or facilitated-control were covered. These include new medical-therapies [serotonin-synthesis inhibitors(telotristat), Pasireotide, new agents for treating ACTHomas], increased dosing with conventional therapies (octreotide-LAR, Lanreotide-Autogel), mTor inhibitors(everolimus), Tyrosine-kinase inhibitors(sunitinib),cytoreductive surgery, liver-directed therapies (embolization, chemoembolization, radioembolization, RFA), peptide radio-receptor-therapy(PRRT) and ¹³¹I-MIBG, ablation of primary F-NETs. Expert opinion: Although many of the newer therapies controlling the hormone-excess-states in F-NETs are reported in relatively few patients, all the approaches show promise. Their description also generates some controversies/unresolved areas,such as the order of these new treatments, their longterm-efficacy, and effectiveness of combinations which may require large,controlled studies.

Long-term outcomes of (131)Iodine mIBG therapy in metastatic gastrointestinal pancreatic neuroendocrine tumours: single administration predicts non-responders

BACKGROUND

(131)Iodine (I131)-metaiodobenzylguanidine (mIBG) is a radionuclide-based treatment option for metastatic gastrointestinal-pancreatic neuroendocrine tumours (GEP NET). This study aimed at identifying prognostic indicators of long-term outcome based on initial evaluation following a first mIBG treatment (7400 MBq) in a patient cohort with such tumours, with a secondary aim of evaluating progression-free survival (PFS) and overall survival (OS) following mIBG therapy.

METHODS

Retrospective review of the hospital records was performed to identify a cohort of 38 adult patients who underwent (131)Iodine-mIBG therapy over a 9-year period for metastatic GEP NETs and neuroendocrine tumours with an unknown primary. Treatment response was evaluated based on radiological criteria (RECIST1.1), biochemical markers [serum Chromogranin A (CgA)/urinary 5HIAA] and symptomatic response at clinical follow-up, all evaluated at 3-6 months from first mIBG treatment. Progression-free survival (PFS) and overall survival (OS) from the first mIBG treatment were recorded.

RESULTS

At 3-6 months following a single mIBG therapy, 75%, 67%, and 63% of patients showed either a partial response (PR) or stable disease (SD) on radiological, biochemical, and symptomatic criteria, respectively. Complete response (CR) was not seen in any patient. OS from the date of diagnosis and from the first therapy was 8 years +/-1.1 (95% CI 5.7 to 10.2 years) and 4 years+/-0.69 (95% CI 2.6-5.3 years), respectively. Twenty-nine percent of patients were alive at 10 years. Significant survival advantage was seen in patients with SD/PR as compared to those who had progressive disease (PD) for each of these three criteria.

CONCLUSION

Biochemical, radiological (RECIST 1.1) and symptomatic assessment of disease status at 3 to 6 months after first I131-mIBG therapy stratifies patients with a poor prognosis. This can be used to identify patients who may benefit from alternative strategies of treatment.

(131)I-MIBG therapy for malignant paraganglioma and phaeochromocytoma: systematic review and meta-analysis

BACKGROUND

(131)I-MIBG therapy can be used for palliative treatment of malignant paraganglioma and phaeochromocytoma. The main objective of this study was to perform a systematic review and meta-analysis assessing the effect of (131)I-MIBG therapy on tumour volume in patients with malignant paraganglioma/phaeochromocytoma.

METHODS

A literature search was performed in December 2012 to identify potentially relevant studies. Main outcomes were the pooled proportions of complete response, partial response and stable disease after radionuclide therapy. A meta-analysis was performed with an exact likelihood approach using a logistic regression with a random effect at the study level. Pooled proportions with 95% confidence intervals (CI) were reported.

RESULTS

Seventeen studies concerning a total of 243 patients with malignant paraganglioma/phaeochromocytoma were treated with (131)I-MIBG therapy. The mean follow-up ranged from 24 to 62 months. A meta-analysis of the effect of (131)I-MIBG therapy on tumour volume showed pooled proportions of complete response, partial response and stable disease of, respectively, 0·03 (95% CI: 0·06-0·15), 0·27 (95% CI: 0·19-0·37) and 0·52 (95% CI: 0·41-0·62) and for hormonal response 0·11 (95% CI: 0·05-0·22), 0·40 (95% CI: 0·28-0·53) and 0·21 (95% CI: 0·10-0·40), respectively. Separate analyses resulted in better results in hormonal response for patients with paraganglioma than for patients with phaeochromocytoma.

CONCLUSIONS

Data on the effects of (131)I-MIBG therapy on malignant paraganglioma/phaeochromocytoma suggest that stable disease concerning tumour volume and a partial hormonal response can be achieved in over 50% and 40% of patients, respectively, treated with (131)I-MIBG therapy. It cannot be ruled out that stable disease reflects not only the effect of MIBG therapy, but also (partly) the natural course of the disease.

Long-term outcome and toxicity after dose-intensified treatment with 131I-MIBG for advanced metastatic carcinoid tumors

Reported experience with systemic (131)I-metaiodobenzylguanidine ((131)I-MIBG) therapy of neuroendocrine tumors comprises different dosing schemes. The aim of this study was to assess the long-term outcome and toxicity of treatment with 11.1 GBq (300 mCi) of (131)I-MIBG per cycle.

METHODS

We performed a retrospective review of 31 patients with advanced metastatic neuroendocrine tumors (20 with carcinoid tumors and 11 with other tumors) treated with (131)I-MIBG. Treatment outcome was analyzed for patients with carcinoid tumors (the most common tumors in this study), and toxicity was analyzed for the entire patient cohort (n = 31). Treatment comprised 11.1 GBq (300 mCi) per course and minimum intervals of 3 mo. The radiographic response was classified according to modified Response Evaluation Criteria in Solid Tumors. Toxicity was determined according to Common Terminology Criteria for Adverse Events (version 3.0) for all laboratory data at regular follow-up visits and during outpatient care, including complete blood counts and hepatic and renal function tests. Survival analysis was performed with the Kaplan-Meier curve method (log rank test; P < 0.05).

RESULTS

The radiographic responses in patients with carcinoid tumors comprised a minor response in 2 patients (10%), stable disease in 16 patients (80%; median time to progression, 34 mo), and progressive disease in 2 patients (10%). The symptomatic responses in patients with functioning carcinoid tumors comprised complete resolution in 3 of the 11 evaluable symptomatic patients (27%), partial resolution in 6 patients (55%), and no significant change in 11 patients. The median overall survival in patients with carcinoid tumors was 47 mo (95% confidence interval, 32-62), and the median progression-free survival was 34 mo (95% confidence interval, 13-55). Relevant treatment toxicities were confined to transient myelosuppression of grade 3 or 4 in 15.3% (leukopenia) and 7.6% (thrombocytopenia) of applied cycles and a suspected late adverse event (3% of patients), myelodysplastic syndrome, after a cumulative administered activity of 66.6 GBq. The most frequent nonhematologic side effect was mild nausea (grade 1 or 2), which was observed in 28% of administered cycles. No hepatic or renal toxicities were noted.

CONCLUSION

Dose-intensified treatment with (131)I-MIBG at a fixed dose of 11.1 GBq (300 mCi) per cycle is safe and offers effective palliation of symptoms and disease stabilization in patients with advanced carcinoid tumors. The favorable survival and limited toxicity suggest that high cycle activities are suitable and that this modality may be used for targeted carcinoid treatment--either as an alternative or as an adjunct to other existing therapeutic options.

Contemporary methods of therapy and follow-up of neuroendocrine tumours of the gastrointestinal tract and the pancreas

The growing interest in neuroendocrine tumours is due to the dynamic growth of detection of this type of cancer. Neuroendocrine tumours (neuroendocrine neoplasms - NENs / neuroendocrine tumours - NETs) derive from glands, groups of endocrine cells and diffuse neuroendocrine system cells. Mainly they derive from the gastrointestinal tract (gastroenteropancreatic-neuroendocrine tumours - GEP-NETs). Currently the modified WHO classification from 2010 is widely used. An important element in the choice of treatment is histological maturity based on mitotic activity and on assessment of proliferation activity (Ki-67). The treatment of choice is surgery. In most cases, complete surgical removal is impossible because of the advanced staging at the time of diagnosis. In well-differentiated neoplasms where the expression of somatostatin receptors is expected, patients are qualified for somatostatin analogues therapy. Poorly differentiated lesions are qualified for chemotherapy. In the guidelines of ENETS (European Neuroendocrine Tumor Society) from 2007 the rules concerning monitoring depending on the WHO classification were specified.

¹¹¹In-DTPA⁰-octreotide (Octreoscan), ¹³¹I-MIBG and other agents for radionuclide therapy of NETs

This paper is a critical review of the literature on NET radionuclide therapy with (111)In-DTPA(0)-octreotide (Octreoscan) and (131)I-MIBG, focusing on efficacy and toxicity. Some potential future applications and new candidate therapeutic agents are also mentioned. Octreoscan has been a pioneering agent for somatostatin receptor radionuclide therapy. It has achieved symptomatic responses and disease stabilization, but it is now outperformed by the corresponding β-emitter agents (177)Lu-DOTATATE and (90)Y-DOTATOC. (131)I-MIBG is the radionuclide therapy of choice for inoperable or metastatic phaeochromocytomas/paragangliomas, which avidly concentrate this tracer via the noradrenaline transporter. Symptomatic, biochemical and tumour morphological response rates of 50-89%, 45-74% and 27-47%, respectively, have been reported. (131)I-MIBG is a second-line radiopharmaceutical for treatment of enterochromaffin carcinoids, mainly offering the benefit of amelioration of hormone-induced symptoms. High specific activity, non-carrier-added (131)I-MIBG and meta-astato((211)At)-benzylguanidine (MABG) are tracers with potential for enhanced therapeutic efficacy, yet their integration into clinical practice awaits further exploration. Amongst other promising agents, radiolabelled exendin analogues show potential for imaging and possibly therapy of insulinomas, while preclinical studies are currently evaluating DOTA peptides targeting the CCK-2/gastrin receptors that are overexpressed by medullary thyroid carcinoma cells.

Repeated Radionuclide therapy in metastatic paraganglioma leading to the highest reported cumulative activity of 131I-MIBG

¹³¹I-MIBG therapy for neuroendocrine tumours may be dose limited. The common range of applied cumulative activities is 10-40 GBq. We report the uneventful cumulative administration of 111 GBq (= 3 Ci) ¹³¹I-MIBG in a patient with metastatic paraganglioma. Ten courses of ¹³¹I-MIBG therapy were given within six years, accomplishing symptomatic, hormonal and tumour responses with no serious adverse effects. Chemotherapy with cisplatin/vinblastine/dacarbazine was the final treatment modality with temporary control of disease, but eventually the patient died of progression. The observed cumulative activity of ¹³¹I-MIBG represents the highest value reported to our knowledge, and even though 12.6 GBq of ⁹⁰Y-DOTATOC were added intermediately, no associated relevant bone marrow, hepatic or other toxicity were observed. In an individual attempt to palliate metastatic disease high cumulative activity alone should not preclude the patient from repeat treatment.

Nuclear medicine techniques for the imaging and treatment of neuroendocrine tumours

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

Matched pairs dosimetry: 124I/131I metaiodobenzylguanidine and 124I/131I and 86Y/90Y antibodies

The technological advances in imaging and production of radiopharmaceuticals are driving an innovative way of evaluating the targets for antineoplastic therapies. Besides the use of imaging to better delineate the volume of external beam radiation therapy in oncology, modern imaging techniques are able to identify targets for highly specific medical therapies, using chemotherapeutic drugs and antiangiogenesis molecules. Moreover, radionuclide imaging is able to select targets for radionuclide therapy and to give the way to in vivo dose calculation to target tissues and to critical organs. This contribution reports the main studies published on matched pairs dosimetry with (124)I/(131)I- and (86)Y/(90)Y-labelled radiopharmaceuticals, with an emphasis on metaiodobenzylguanidine (MIBG) and monoclonal antibodies.

Molecular tracers for the PET and SPECT imaging of disease

The development of positron emission tomography (PET) and single photon emission computed tomography (SPECT) imaging continues to grow due to the ability of these techniques to allow the non-invasive in vivo visualisation of biological processes at the molecular and cellular levels. As well as finding application for the diagnosis of disease, these techniques have also been used in the drug discovery process. Crucial to the growth of these techniques is the continued development of molecular probes that can bind to the target biological receptor with high selectivity. This tutorial review describes the use of PET and SPECT for molecular imaging and highlights key strategies for the development of molecular probes for the imaging of both cancer and neurological diseases.

131I-metaiodobenzylguanidine therapy of neuroblastoma and other neuroendocrine tumors

Treatment with (131)I-metaiodobenzylguanidine (MIBG) has been introduced to the management of neuroendocrine tumors (NET) nearly 30 years ago. It provides efficient internal radiotherapy of chromaffin tumors (neuroblastoma, pheochromocytoma, and paraganglioma), but also of carcinoid and other less frequent tumors. Although for various NET types the role of this treatment form decreased by the emergence of peptide receptor radionuclide therapy, (131)I-MIBG still remains the primary radiopharmaceutical for targeting chromaffin tumors with outstanding efficiency. Results in neuroblastoma with overall response rates around 30% in refractory or recurrent diseases have been improved by combinations with chemotherapy, radiosensitizers, and autologous stem cell support. For adult chromaffin tumors, that is, pheochromocytoma and/or paraganglioma, (131)I-MIBG therapy is currently the most efficient nonsurgical therapeutic modality and applies for inoperable, disseminated disease. The antisecretory effect with powerful palliation of symptomatic disease (response rate: 75%-90%) should also be considered when judging treatment benefit. The results in carcinoid tumors are less pronounced, primarily achieving arrest of tumor growth, and most importantly effective functional control. With the presence of peptide receptor radionuclide therapy, (131)I-MIBG remains the alternative radionuclide in this tumor entity, for example, for patients with renal impairment. Another worthwhile mentioning indication-although less prevalent-are metastatic medullary thyroid carcinomas, especially if functioning. These patients are good candidates for this treatment form in the absence of reasonable surgical options and presence of diagnostic MIBG uptake. This article outlines the current status, results, and methodological improvements of (131)I-MIBG therapy.

Radioiodinated metaiodobenzylguanidine treatment of neuroendocrine tumors in adults

Metaiodobenzylguanidine (MIBG), radioiodinated with (131)I, has been available for 25 years. Its role in the United States is limited to diagnostic imaging, whereas its therapeutic application in patients with neuroendocrine tumors for whom surgical treatment would not lead to a cure, has been approved in Europe. (131)I-MIBG treatments can be a valuable addition to the current gamut of treatment options for patients with metastatic neuroendocrine tumors, especially given the limited role for other systemic treatments, such as chemotherapy. There are basically two treatment strategies: one or two high-dose treatments or continuous low-dose treatments. (131)I-MIBG could induce symptomatic relief in the vast majority of patients treated, both following high-dose treatment and low-dose maintenance treatment. Biochemical responses can be observed in about half of the patients, whereas radiographic responses are described in roughly one third of the patients. Several articles suggested a survival benefit to patients treated with (131)I-MIBG. Side-effects of the treatment mainly consist of myelotoxicity, nausea, and hypothyroidism. Future developments are focused on the use of high-specific-activity (131)I-MIBG in high doses. The role of (131)I-MIBG in relation to other treatments remains to be established, although treatment (131)I-MIBG seems to be at least as effective as other systemic treatments, with limited side-effects.

Modeling Combined Radiopharmaceutical Therapy: A Linear Optimization Framework

In this paper, we investigate a previously proposed mathematical model describing the effects that an innovative combined radiopharmaceutical therapy might have on the delivery of radiation to the tumor and limiting critical organs. While focused on a specific dual agent therapy, this investigation will prove mathematically that for any two therapeutic radiopharmaceuticals with different limiting critical organs the model provides patient specific conditions under which combination therapy is superior to single agent therapy. In addition, this paper outlines general methods for calculating the amounts of administered radioactivity for each drug required to optimize tumor radiation dose. We also consider extensions of this model to include an arbitrary number of independent radiopharmaceuticals and/or other treatment factors.

Surgery in malignant pancreatic neuroendocrine tumors

BACKGROUND

Because of their rarity and indolent nature, optimal management of malignant pancreatic neuroendocrine tumors remains controversial. The purpose of this study is to review a series of patients with these tumors and investigate the role of surgery in the treatment.

METHODS

A retrospective study of 73 patients (ages 24-86 years; 36 women) undergoing treatment at a tertiary academic medical center was performed. Patient demographics, diagnostic tests, operations, pathologic findings, adjuvant treatments, and survival were reviewed.

RESULTS

Seventy-four percent of patients had advanced disease with hepatic metastases and 30% had functional tumors. Fifty-seven percent of the patients underwent pancreatic resections. Two 60-day mortalities occurred and the postoperative complication rate was 27%. Overall 5-year survival rate was 44%. There was no difference in survival between patients with functional and nonfunctional tumors. Patients undergoing resection, even in metastatic disease, had better survival than patients who had no resection (60% vs. 30%, P = 0.025). Recurrence occurred in 20% of patients who underwent a curative resection.

CONCLUSION

Patients with malignant pancreatic neuroendocrine tumors commonly present with advanced disease. Although, curative resection is not frequent, survival benefit may be obtainable with aggressive surgical management even in the face of metastatic disease.

A kit method for the high level synthesis of [211At]MABG

meta-[(211)At]Astatobenzylguanidine ([(211)At]MABG), an analogue of meta-iodobenzylguanidine (MIBG) labeled with the alpha-emitter (211)At, targets the norepinephrine transporter. Because MABG has been shown to have excellent characteristics in preclinical studies, it has been considered to be a promising targeted radiotherapeutic for the treatment of tumors such as micrometastatic neuroblastoma that overexpress the norepinephrine transporter. To facilitate clinical evaluation of this agent, a convenient method for the high level synthesis of [(211)At]MABG that is adaptable for kit formulation has been developed. A tin precursor anchored to a solid-support was treated with a methanolic solution of (211)At in the presence of a mixture of H(2)O(2)/HOAc as the oxidant; [(211)At]MABG was isolated by simple solid-phase extraction. By using C-18 solid-phase extraction, the radiochemical yield from 25 batches was 63+/-13%; however, loss of radioactivity during evaporation of the methanolic solution was a problem. This difficulty was avoided by use of a cation exchange resin cartridge for isolation of [(211)At]MABG, which resulted in radiochemical yields of 63+/-9% in a shorter duration of synthesis. The radiochemical purity was more than 90% and no chemical impurity has been detected. The final doses were sterile and apyrogenic. These results demonstrate that [(211)At]MABG can be prepared via a kit method at radioactivity levels anticipated for initiation of clinical studies.

Is MIBG a substrate of P-glycoprotein?

PURPOSE

Radionuclide therapy with 131I-labelled meta-iodobenzylguanidine ([131I]MIBG) is effective in cases where it is difficult to carry out surgical resection or debulking of neuroendocrine tumours (NETs). However, it has recently been reported that P-glycoprotein (P-gp) is expressed in these NETs. Therefore, it is important to clarify whether MIBG is a substrate of P-gp or not. In this study, using a human cell line which overexpresses P-gp, LLC-GA5-COL150, we investigated this question.

METHODS

The transcellular transport and accumulation of [125I]MIBG were measured using monolayer cultures grown in Transwell chambers. [125I]MIBG was added to either the basolateral or the apical side, aliquots of the incubation medium on the other side were taken at specified times, and the radioactivity was measured. For accumulation experiments, the cells on the filters were solubilised and the radioactivity in aliquots was measured.

RESULTS

There were no significant differences in the transport of MIBG between LLC-PK1 and LLC-GA5-COL150 monolayers in either direction until 60 min. With respect to the accumulation of MIBG, there were no significant differences between LLC-PK1 and LLC-GA5-COL150 cells in either direction.

CONCLUSION

MIBG is not a substrate of P-gp. Therefore, radionuclide therapy with MIBG would be useful in the treatment of NETs expressing P-gp.

Courses of Malignant Pheochromocytoma: Implications for Therapy

Survival of patients with metastatic pheochromocytoma that have exceeded 30 years without therapy to reduce tumors have been reported. We reviewed the records of 38 patients with malignant pheochromocytoma who had received 131I-metaiodiobenzylguanidine (131I-MIBG) treatments between 1981 and 1996 to evaluate longevity. Survival from diagnosis to last follow-up exceeded 5 years in 21 of 38 (55%) and >or=10 years in 50%. In 17 of 21, the interval from diagnosis to 131I-MIBG therapy was greater than 5 years. Survival following 131I-MIBG was >or=5 years in 12 of 17 and >or=10 years in 7 of 17 patients despite continued evidence of excessive circulating catecholamines. Objective responses to 131I-MIBG therapy were seen in about 30% and were usually of a few years, duration, but one individual exhibited marked reductions in volume and function of tumors that have persisted for 21 years. No feature, including a remission of >5 years following surgical excision, was found to predict prolonged survival. In summary, many patients with malignant pheochromocytoma will follow a course extending over many years. The role of 131I-MIBG therapy in longevity is uncertain, but this radiopharmaceutical reduces evidence of tumors in some patients. Criteria for selecting patients who will benefit from treatment remain to be determined.

Radiofrequency ablation of neuroendocrine liver metastases: the Middlesex experience

BACKGROUND

Current treatment options for neuroendocrine liver metastases are not widely applicable or not that effective. Image-guided thermal ablation offers the possibility of a minimally invasive, albeit palliative, treatment that decreases tumor volume, preserves most of the normal liver, and can be repeated several times. We report our experience with image-guided thermal ablation in 25 patients with unresectable liver metastases.

METHODS

Since 1990 we have treated 189 tumors at 66 treatment sessions in 25 patients (12 female, 13 male; median age, 56 years; age range, 26--78 years). Thirty treatments were performed with a solid-state laser, and 36 treatments were performed with radiofrequency ablation. All but one treatment was performed percutaneously under image guidance. Sixteen patients had metastases from carcinoid primaries, three from gastrinoma, two from insulinoma, and four from miscellaneous causes. Fourteen of 25 had symptoms from hormone secretion.

RESULTS

Imaging follow-up was available in 19 patients at a median of 21 months (range, 4--75 months). There was a complete response in six patients, a partial response in seven, and stable disease in one; hence, tumor load was controlled in 14 of 19 patients (74%). Relief of hormone-related symptoms was achieved in nine of 14 patients (69%). The median survival period from the diagnosis of liver metastases was 53 months. One patient with end-stage cardiac disease died after a carcinoid crisis. There were eight (12%) complications: five local and three distant, four major and four minor.

CONCLUSIONS

As a minimally invasive, readily repeatable procedure that can be used to ablate small tumors, preferably before patients become severely symptomatic, radiofrequency ablation can provide effective control of liver tumor volume in most patients over many years.

Long-term efficacy of low activity meta-[131I]iodobenzylguanidine therapy in patients with disseminated neuroendocrine tumours depends on initial response

BACKGROUND

meta-[131I]Iodobenzylguanidine (131I-MIBG) has been used to treat patients with disseminated neuroendocrine tumours (NET). However, so far there is limited information related to the efficacy of this agent beyond the normal 6-month assessment period. Before we can assume that such treatment would be beneficial to patients with these tumours the outcome of the patients over a longer time course should be determined. In many centres financial or radiation protection constraints mean that lower activities of 131I-MIBG have to be used at each administration, therefore instead of giving a single administration of a higher activity 131I-MIBG a series of multiple lower activity administrations are used.

METHODS

The case records of 25 patients who had received 131I-MIBG over a 4-year period, from 1 June 1997 to 30 June 2001, were reviewed. Overall time of clinical follow-up range from 1 to 60 months, with a mean of 16 months). There were 16 female and nine male patients (mean age 55.6 years; range, 30-79 years). Most of patients had carcinoid (17), two had phaeochromocytoma, two gastrinoma and two an undifferentiated NET, one had malignant paraganglioma and one had medullary cell carcinoma of the thyroid. All had avid uptake for 123I-MIBG on diagnostic scanning. The minimum number of treatments received was 1 in 4 patients (with activities of 2.0 to 3.4 GBq); the maximum was 11 treatments (with cumulative activities as high as 29.1 GBq). Treatment was given using an infusion pump and was normally repeated at 12- to 16-week intervals (mean number of treatments per patient, 4). Response to therapy was determined by changes in the size of the tumour on computed tomography and/or magnetic resonance imaging using the response evaluation criteria in solid tumours (RECIST). Toxicity was measured using blood and urine tests of renal, hepatic, thyroid and bone marrow function. The median time from the last treatment to progression of disease and death (if applicable) was also calculated.

RESULTS

No significant or long-lasting toxicity was encountered. At 6 months after the patient's last treatment, 18 patients (72%) had no evidence for progression. Twelve months after their last treatment 12 (48%) patients had no evidence for progression. At 18 months after the patient's last treatment, only seven patients (28%) had no progression of their disease. Overall, the median progression-free survival was 15 months. In those patients with stability or response at 6 months there was a prolonged progression-free survival and overall survival. In those with progression of disease at 6 months, at the 6-month assessment point, there had been four deaths (16%), at 12 months, there were three additional cancer deaths and finally at 18 months, there were a further five deaths. The median survival was 18 months. In those patients who died the mean time interval between disease progression and death was 4.6 months (range 0-12 months).

CONCLUSION

Of the patients treated with low-activity 131I-MIBG 68% had significant benefit for at least 6 months post-treatment. In these patients with progressive and extensive disease this technique provided prolonged progression-free and overall survival with minimal side effects especially if an initial response to treatment was seen.

[Octreotide + bilateral adrenalectomy in the management of ACTH-producing carcinoid tumors]

Cushing's syndrome (CS) due to ectopic ACTH secretion has a high morbidity and mortality. Thus, rapid treatment of ectopic CS is mandatory. Carcinoid tumors associated with ectopic ACTH (CTu-ACTH) syndrome represent a more severe clinical picture, due to the carcinoid symptoms that worsen the hypercortisolism state. Management of patients with CTu-ACTH should include the control of hypercortisolism, as well as the carcinoid disturbance. We report 3 patients (2F, 1M) with CTu-ACTH (2 pancreatic, 1 occult) who presented with clinical manifestations of CS (n= 3) and carcinoid syndrome (2): 2 were initially investigated for CS and 1 carcinoid syndrome. In all hypokalemia, hypertension and diabetes mellitus were associated with severe hypercortisolism and high ACTH levels. Administration of octreotide-LAR reduced ACTH levels from 230,000 to 30,000 pg/ml in patient 1, and controlled symptoms of carcinoid syndrome and neoplasic lesions in patient 2; treatment with subcutaneous octreotide in patient 3 controlled carcinoid syndrome and partially reduced symptoms of hypercortisolism. All 3 patients were submitted to bilateral adrenalectomy to control CS. Our data show that combined anti-neoplastic therapy may contribute to the stabilization and/or definitive control of CTu-ACTH.

Repeated [131I]metaiodobenzylguanidine therapy in two patients with malignant pheochromocytoma

CONTEXT

Approximately 10% of pheochromocytomas are malignant with a 5-yr survival rate of less than 40%. Promising results have been published on single high-dosage [131I]metaiodobenzylguanidine ([131I]MIBG) treatment for malignant pheochromocytoma. We present our experience with multiple intermediate-dosage [131I]MIBG therapy instead of single high-dosage therapy.

SETTING AND PATIENTS

The study took place at University Medical Centers and included two patients (one male, 36 yr of age, and one female, 43 yr of age) with widely spread metastatic pheochromocytoma and bad prognosis because of liver and lung metastases.

INTERVENTIONS

Instead of a single high dosage, these two patients were treated with multiple intermediate dosages of [131I]MIBG. The first patient received 37 GBq (1 Ci) [131I]MIBG in five sessions [7400 MBq (200 mCi) each; interval range, 2-11 months]; the second patient received 66.6 GBq (1.8 Ci) [131I]MIBG in 12 sessions [5550 MBq (150 mCi) each; interval range, 2-14 months].

OUTCOME MEASURES

We measured efficacy, toxicity, and survival.

RESULTS

Both patients had a complete symptomatic response and a partial tumor volume response. The first patient had a partial biochemical response, the second a complete biochemical response. In both cases, toxicity has been confined to nausea during treatment. Hematological toxicity was minimal, and both patients stayed euthyroid. The survival (so far) of these patients was 5 yr (clinical case 1) and 16 yr (clinical case 2) after initial diagnosis.

CONCLUSIONS

Repeated intermediate-dosage [131I]MIBG treatment appears to be a reliable and well-tolerated radionuclide therapy and might be a useful adjunct in patients with malignant pheochromocytoma, providing longstanding palliation and prolonged survival.

The diagnosis and medical management of advanced neuroendocrine tumors

Neuroendocrine tumors (NETs) constitute a heterogeneous group of neoplasms that originate from endocrine glands such as the pituitary, the parathyroids, and the (neuroendocrine) adrenal, as well as endocrine islets within glandular tissue (thyroid or pancreatic) and cells dispersed between exocrine cells, such as endocrine cells of the digestive (gastroenteropancreatic) and respiratory tracts. Conventionally, NETs may present with a wide variety of functional or nonfunctional endocrine syndromes and may be familial and have other associated tumors. Assessment of specific or general tumor markers offers high sensitivity in establishing the diagnosis and can also have prognostic significance. Imaging modalities include endoscopic ultrasonography, computed tomography and magnetic resonance imaging, and particularly, scintigraphy with somatostatin analogs and metaiodobenzylguanidine. Successful treatment of disseminated NETs requires a multimodal approach; radical tumor surgery may be curative but is rarely possible. Well-differentiated and slow-growing gastroenteropancreatic tumors should be treated with somatostatin analogs or alpha-interferon, with chemotherapy being reserved for poorly differentiated and progressive tumors. Therapy with radionuclides may be used for tumors exhibiting uptake to a diagnostic scan, either after surgery to eradicate microscopic residual disease or later if conventional treatment or biotherapy fails. Maintenance of the quality of life should be a priority, particularly because patients with disseminated disease may experience prolonged survival.