Assessment of the efficacy and toxicity of (131)I-metaiodobenzylguanidine therapy for metastatic neuroendocrine tumours

Effects of Repeated 131I-Meta-Iodobenzylguanidine Radiotherapy on Tumor Size and Tumor Metabolic Activity in Patients with Metastatic Neuroendocrine Tumors

¹³¹I-meta-iodobenzylguanidine (¹³¹I-MIBG) radiotherapy has shown some survival benefits in metastatic neuroendocrine tumors (NETs). European Association of Nuclear Medicine clinical guidelines for ¹³¹I-MIBG radiotherapy suggest a repeated treatment protocol, although none currently exists. The existing single-high-dose ¹³¹I-MIBG radiotherapy (444 MBq/kg) has been shown to have some benefits for patients with metastatic NETs. However, this protocol increases adverse effects and requires alternative therapeutic approaches. Therefore, the aim of this study was to evaluate the effects of repeated ¹³¹I-MIBG therapy on tumor size and tumor metabolic response in patients with metastatic NETs. Methods: Eleven patients with metastatic NETs (aged 49.2 ± 16.3 y) prospectively received repeated 5,550-MBq doses of ¹³¹I-MIBG therapy at 6-mo intervals. In total, 31 treatments were performed. The mean number of treatments was 2.8 ± 0.4, and the cumulative ¹³¹I-MIBG dose was 15,640.9 ± 2,245.1 MBq (286.01 MBq/kg). Tumor response was observed by CT and ¹⁸F-FDG PET or by ¹⁸F-FDG PET/CT before and 3-6 mo after the final ¹³¹I-MIBG treatment. Results: On the basis of the CT findings with RECIST, 3 patients showed a partial response and 6 patients showed stable disease. The remaining 2 patients showed progressive disease. Although there were 2 progressive-disease patients, analysis of all patients showed no increase in summed length diameter (median, 228.7 mm [interquartile range (IQR), 37.0-336.0 mm] to 171.0 mm [IQR, 38.0-270.0 mm]; P = 0.563). In tumor region-based analysis with partial-response and stable-disease patients (n = 9), ¹³¹I-MIBG therapy significantly reduced tumor diameter (79 lesions; median, 16 mm [IQR, 12-22 mm] to 11 mm [IQR, 6-16 mm]; P < 0.001). Among 5 patients with hypertension, there was a strong trend toward systolic blood pressure reduction (P = 0.058), and diastolic blood pressure was significantly reduced (P = 0.006). Conclusion: Eighty-two percent of metastatic NET patients effectively achieved inhibition of disease progression, with reduced tumor size and reduced metabolic activity, through repeated ¹³¹I-MIBG therapy. Therefore, this relatively short-term repeated ¹³¹I-MIBG treatment may have potential as one option in the therapeutic protocol for metastatic NETs. Larger prospective studies with control groups are warranted.

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.

Current Consensus on I-131 MIBG Therapy

Metaiodobenzylguanidine (MIBG) is structurally similar to the neurotransmitter norepinephrine and specifically targets neuroendocrine cells including some neuroendocrine tumors. Iodine-131 (I-131)-labeled MIBG (I-131 MIBG) therapy for neuroendocrine tumors has been performed for more than a quarter-century. The indications of I-131 MIBG therapy include treatment-resistant neuroblastoma (NB), unresectable or metastatic pheochromocytoma (PC) and paraganglioma (PG), unresectable or metastatic carcinoid tumors, and unresectable or metastatic medullary thyroid cancer (MTC). I-131 MIBG therapy is one of the considerable effective treatments in patients with advanced NB, PC, and PG. On the other hand, I-131 MIBG therapy is an alternative method after more effective novel therapies are used such as radiolabeled somatostatin analogs and tyrosine kinase inhibitors in patients with advanced carcinoid tumors and MTC. No-carrier-aided (NCA) I-131 MIBG has more favorable potential compared to the conventional I-131 MIBG. Astatine-211-labeled meta-astatobenzylguanidine (At-211 MABG) has massive potential in patients with neuroendocrine tumors. Further studies about the therapeutic protocols of I-131 MIBG including NCA I-131 MIBG in the clinical setting and At-211 MABG in both the preclinical and clinical settings are needed.

Molecular radiotheranostics for neuroendocrine tumours

This article discusses the important role of nuclear medicine imaging and therapy in the management of neuroendocrine tumours (NETs). Somatostatin receptor scintigraphy has a high impact on patient management versus conventional imaging. Molecular radiotherapy is an important part of the management of patients with NETs. Selection of patients for molecular radiotherapy in NETs is based on uptake on their radionuclide imaging study. The imaging agent has the same mechanism of uptake as the therapeutic agent. Thus, the imaging study preselects patients that are likely to concentrate radiation within their tumours.

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.

Feasibility and advantage of adding (131)I-MIBG to (90)Y-DOTATOC for treatment of patients with advanced stage neuroendocrine tumors

Background

Peptide receptor radionuclide therapy (PRRT) is an effective form of treatment for patients with metastatic neuroendocrine tumors (NETs). However, delivering sufficient radiation dose to the tumor to result in a high percentage of long-term tumor remissions remains challenging because of the limits imposed on administered activity levels by radiation damage to normal tissues. The goal of this study was to evaluate the dosimetric advantages of adding ¹³¹I meta-iodobenzylguanidine (¹³¹I-MIBG) to ⁹⁰Y DOTA Phe1-Tyr3-octreotide (⁹⁰Y-DOTATOC) in patients with advanced stage midgut NETs.

Methods

Ten patients were imaged simultaneously with ¹³¹I-MIBG and ¹¹¹In-pentetreotide (as a surrogate for ⁹⁰Y-DOTATOC) on days 1, 2, and 3 post-administration. Blood samples were obtained at the same time points. Using dosimetry measures from this data and our previously published methodology for calculating optimal combined administered activity levels for therapy, we determined the amount of ¹³¹I-MIBG that could be added to ⁹⁰Y-DOTATOC without exceeding normal organ dose limits (marrow and kidneys) along with the expected increase in associated tumor dose, if any.

Results

We found that a median value of 34.6 GBq of ¹³¹I-MIBG could be safely added to ⁹⁰Y-DOTATOC (delivered over multiple cycles) by reducing the maximum total deliverable ⁹⁰Y-DOTATOC by a median value of 24.5%. Taking this treatment approach, we found that there would be a median increase in deliverable tumor dose of 4,046 cGy in six of the ten subjects. Of note, there were a small number of metastases that were positive for only one or the other of these radiopharmaceuticals within the same subject.

Conclusions

We conclude that approximately half of the patients with midgut NETs that are eligible for PRRT could reasonably be expected to benefit from the addition of ¹³¹I-MIBG to ⁹⁰Y-DOTATOC.

Effects and safety of ¹³¹I-metaiodobenzylguanidine (MIBG) radiotherapy in malignant neuroendocrine tumors: results from a multicenter observational registry

Effective treatments for malignant neuroendocrine tumors are under development. While iodine-131 metaiodobenzylguanidine (¹³¹I-MIBG) radiotherapy has been used in the treatment of malignant neuroendocrine tumors, there are few studies evaluating its therapeutic effects and safety in a multicenter cohort. In the current study, we sought to evaluate the effects and safety of ¹³¹I-MIBG therapy for conditions including malignant pheochromocytoma and paraganglioma within a multicenter cohort. Forty-eight malignant neuroendocrine tumors (37 pheochromocytoma and 11 paraganglioma) from four centers underwent clinical ¹³¹I-MIBG radiotherapy. The tumor responses were observed before and 3 to 6 months after the ¹³¹I-MIBG radiotherapy in accordance with RECIST criteria. We also evaluated the data for any adverse effects. The four centers performed a total of 87 ¹³¹I-MIBG treatments on 48 patients between January 2000 and March 2009. Of the treatments, 65 were evaluable using RECIST criteria. One partial response (PR), 40 stable disease (SD), and 9 progressive disease (PD) in malignant pheochromocytoma were observed after each treatment. Fourteen SD and one PD-were observed in paraganglioma. Patients with normal hypertension (systolic blood pressure (BP) > 130 mmHg) showed significantly reduced systolic BP after the initial follow-up (n=10, 138.1±8.2 to 129.5±13.5 mmHg, P=0.03). In adult neuroendocrine tumors with a treatment-basis analysis, there were side effects following 41 treatments (47.1%) and most of them (90.2%) were minor. In this multicenter registry, PR or SD was achieved in 84.6% of the treatment occasions in adult neuroendocrine tumors through ¹³¹I-MIBG radiotherapy. This indicated that most of the ¹³¹I-MIBG radiotherapy was performed safely without significant side effects.

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.

Sequelae and survivorship in patients treated with (131)I-MIBG therapy

Background:

¹³¹I-meta-iodobenzylguanidine (¹³¹I-MIBG) has been in therapeutic use since 1980s. Newer treatment modalities are emerging for neuroendocrine tumours (NETs) and chromaffin cell tumours (CCTs), but many of these do not yet have adequate long-term follow-up to determine their longer term efficacy and sequelae.

Methods:

Fifty-eight patients with metastatic NETs and CCTs who had received ¹³¹I-MIBG therapy between 2000 and 2011 were analysed. Survival and any long-term haematological or renal sequelae were investigated.

Results:

In the NET group, the overall median survival and median survival following the diagnosis of metastatic disease was 124 months. The median survival following the commencement of ¹³¹I-MIBG was 66 months. For the CCT group, median survival had not been reached. The 5-year survival from diagnosis and following the diagnosis of metastatic disease was 67% and 67.5% for NETs and CCTs, respectively. The 5-year survival following the commencement of ¹³¹I-MIBG therapy was 68%. Thirty-two patients had long-term haematological sequelae: 5 of these 32 patients developed haematological malignancies. Two patients developed a mild deterioration in renal function.

Conclusion:

Long follow up of ¹³¹I-MIBG therapy reveals a noteable rate of bone marrow toxicities and malignancy and long term review of all patients receiving radionuclide therapies is recommended.

Peptide receptor radionuclide therapy with (90)Y-DOTATATE/(90)Y-DOTATOC in patients with progressive metastatic neuroendocrine tumours: assessment of response, survival and toxicity

Background:

Peptide receptor radionuclide therapy (PRRT) is an established treatment for patients with metastatic neuroendocrine tumours (NETs), although which factors are associated with an improved overall survival (OS) remains unclear. The primary aim of this study is to determine to what extent a radiological response to ⁹⁰Y-DOTATOC/⁹⁰Y-DOTATATE PRRT is associated with an improved OS. The association of biochemical and clinical response to OS were assessed as secondary outcome measures.

Methods:

A retrospective analysis was conducted on 57 patients: radiological response was classified using RECIST criteria, biochemical response was classified using WHO criteria and clinical response was assessed subjectively. Responses were recorded as positive response (PR), stable disease (SD) or progressive disease (PD), and survival analysed.

Results:

Radiological response was achieved in 71.5% (24.5% PR, 47% SD) and was associated with a greater OS (51 and 56 months, respectively), compared with PD (18 months). A biochemical or clinical response post PRRT were not associated with a statistically significant improvement in OS. However, when combined with radiological response a survival benefit was observed according to the number of outcomes (radiological, biochemical, clinical), in which a response was observed. Mild haematological toxicity was common, renal toxicity was rare.

Conclusion:

In patients with progressive metastatic NETs receiving ⁹⁰Y-DOTATOC/⁹⁰Y-DOTATATE PRRT, a radiological response with either a PR or a SD post therapy confers a significant OS benefit.

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.

Clinical significance of 2-[18F]fluoro-2-deoxy-D-glucose positron emission tomography for the assessment of 131I-metaiodobenzylguanidine therapy in malignant phaeochromocytoma

PURPOSE

The aim of this study was to evaluate the significance of 2-[18F]fluoro-2-deoxy-D-glucose (FDG) positron emission tomography (PET) in the assessment of the therapeutic response to 131I-metaiodobenzylguanidine (MIBG) in malignant phaeochromocytoma.

METHODS

We reviewed the records of 11 patients (7 men and 4 women) with malignant phaeochromocytoma who underwent 131I-MIBG therapy (100-200 mCi). 18F-FDG PET and serum catecholamine assays were performed 3 months before and after the first dose of 131I-MIBG. FDG uptake was evaluated in the observed lesions using the maximum standardised uptake value (SUVmax). The average SUVmax of all lesions (ASUV) was calculated. If more than five lesions were identified, the average SUVmax of the five highest SUVmax (ASUV5) was calculated. The ratio of pre- and post-therapy values was calculated for the highest SUVmax (rMSUV), ASUV (rASUV), ASUV5 (rASUV5), CT diameter (rCT) and serum catecholamine (rCA). Responder (R) and non-responder (NR) groups were defined after a clinical follow-up of at least 6 months according to changes in symptoms, CT, magnetic resonance imaging (MRI) and 123I-MIBG scan.

RESULTS

Post-therapy evaluation revealed five R and six NR patients. The size of the target lesions was not significantly different before and after therapy (p>0.05). However, ASUV and ASUV5 were significantly lower in the R group (rASUV 0.64±0.18, rASUV5 0.68±0.17) compared to the NR group (rASUV 1.40±0.54, rASUV5 1.37±0.61) (p<0.05).

CONCLUSION

18F-FDG PET can be potentially used to evaluate the response of malignant phaeochromocytoma to 131I-MIBG therapy.

PET imaging of norepinephrine transporter-expressing tumors using 76Br-meta-bromobenzylguanidine

Meta-iodobenzylguanidine (MIBG) labeled with (123)I or (131)I has been widely used for the diagnosis and radiotherapy of norepinephrine transporter (NET)-expressing tumors. However, (123)I/(131)I-MIBG has limitations for detecting small lesions because of its lower spatial resolution than PET tracers. In this study, meta-bromobenzylguanidine (MBBG) labeled with (76)Br (half-life, 16.1 h), an attractive positron emitter, was prepared and evaluated as a potential PET tracer for imaging NET-expressing tumors.

METHODS

(76)Br-MBBG was prepared by a halogen-exchange reaction between the (76)Br and iodine of nonradioactive MIBG. The stability of MBBG was evaluated in vitro and in vivo by high-performance liquid chromatography analysis. Cellular uptake studies with or without NET inhibitors were performed in NET-positive PC-12 cell lines. Biodistribution studies were performed in PC-12 tumor-bearing nude mice by administration of a mixed solution of MBBG, MIBG, and (18)F-FDG. The tumor was imaged using (76)Br-MBBG and (18)F-FDG with a small-animal PET scanner.

RESULTS

MBBG was stable in vitro, but some time-dependent dehalogenation was observed after administration in mice. MBBG showed high uptake in PC-12 tumor cells that was significantly decreased by the addition of NET inhibitors. In biodistribution studies, MBBG showed high tumor accumulation (32.0 +/- 18.6 percentage injected dose per gram at 3 h after administration), and the tumor-to-blood ratio reached as high as 54.4 +/- 31.9 at 3 h after administration. The tumor uptake of MBBG correlated well with that of MIBG (r = 0.997) but not with that of (18)F-FDG. (76)Br-MBBG PET showed a clear image of the transplanted tumor, with high sensitivity, which was different from the lesion shown by (18)F-FDG PET.

CONCLUSION

(76)Br-MBBG showed high tumor accumulation, which correlated well with that of MIBG, and provided a clear PET image. These results indicated that (76)Br-MBBG would be a potential PET tracer for imaging NET-expressing neuroendocrine tumors and could provide useful information for determining the indications for (131)I-MIBG therapy.

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.

Efficacy of using a standard activity of (131)I-MIBG therapy in patients with disseminated neuroendocrine tumours

PURPOSE

The aim of this analysis was to evaluate the response to standard activity of (131)I-meta-iodobenzylguanidine (MIBG) in patients with disseminated neuroendocrine tumours (NETs), comparing overall survival of patients with symptomatic response, tumour size (as assessed by CT) and relevant plasma tumour markers.

METHODS

A retrospective review of patients who had undergone (131)I-MIBG treatment between March 2001 and December 2006 was carried out. The administered activity of (131)I-MIBG was 5.5 GBq (NETs) and 7 GBq (phaeochromocytoma). Three cycles of treatment were planned with an interval of 10-12 weeks. A pre-therapy scan with (123)I-MIBG was performed to ascertain appropriate biodistribution.

RESULTS

Thirty-eight patients were identified. Only two patients developed significant bone marrow suppression. Symptomatic response: data were available in 37 of 38 patients: 15 patients had improved symptoms, 19 had no improvement in symptoms and 3 were asymptomatic. In those with a symptomatic response, the median overall survival was 58 months vs no response of 20.0 months (p = 0.001). CT response: in those with stable disease, the median overall survival was 58 months compared with progressive disease of 16.0 months. The difference between these groups was significant (p = 0.006). Hormonal response: this was available in only 20 of 38 patients. The median overall survival was the same for patients that had increased hormone levels and patients that had stable/decreased hormone levels (48 months).

CONCLUSION

Standard activity (131)I-MIBG is well tolerated. Symptomatic response to treatment is a significant predictor of overall survival. Whilst CT response also appears to predict survival, hormonal levels do not appear to correlate with survival.