Prognostic value of [18F]FDG-PET prior to [131I]MIBG treatment for pheochromocytoma and paraganglioma (PPGL)

Urinary Dopamine Levels Can Predict the Avidity of Post-Therapy [131I]MIBG Scintigraphy in Unresectable or Metastatic Pheochromocytomas and Paragangliomas: A Preliminary Clinical Study

Background/Objectives: Pheochromocytomas and paragangliomas (PPGLs) are rare neuroendocrine tumors that produce catecholamines. Unresectable or metastatic PPGLs are treated with [131I]metaiodobenzylguanidine (MIBG), but MIBG avidity is often heterogeneous. Identifying predictive factors for non-avid lesions on scintigraphy is clinically important. The primary objective of this study was to investigate the relationship between MIBG avidity and catecholamine secretion patterns in patients with unresectable or metastatic PPGLs. Methods: This retrospective study included 27 patients treated with [131I]MIBG for unresectable/metastatic PPGLs between 2001 and 2024. Patients received a single intravenous dose of [131I]MIBG (5.5-7.4 GBq), with post-therapy scintigraphy performed 3-7 days later. Non-avid lesions were assessed by imaging and confirmed using CT, MRI, and FDG-PET. Clinical factors, including age, sex, prior treatments, metastasis sites, and urine catecholamines, were evaluated using univariate logistic analysis. Predictive factors were assessed via receiver operating characteristic curves. Results: Non-avid lesions were found in nine patients (33.3%). These patients were younger (median age 38 vs. 62.5 years) and had higher urine dopamine levels (median 1510 vs. 779 μg/day) than those without non-avid lesions. Younger age (odds ratio: 0.892, p < 0.01) and higher urinary dopamine levels (odds ratio: 1.003, p < 0.01) were significantly associated with non-avid lesions. All patients > 45 years with urinary dopamine < 1190 μg/day had no non-avid lesions, whereas patients < 45 years with urinary dopamine > 1190 μg/day had non-avid lesions. Conclusions: Age and urinary dopamine levels may predict non-avid lesions in unresectable/metastatic PPGLs, aiding treatment decisions for [131I]MIBG therapy. This article is a revised and expanded version of a paper entitled "Urine dopamine level and age can predict non-avid lesion on scintigraphy after I-131 MIBG treatment for unresectable/metastatic PPGL", which was presented at SNMMI 2024, Toronto, from 8 June to 11 June 2024.

Approach to the Patient: Concept and Application of Targeted Radiotherapy in the Paraganglioma Patient

Paragangliomas can metastasize, posing potential challenges both in symptomatic management and disease control. Systemic targeted radiotherapies using 131I-MIBG and 177Lu-DOTATATE are a mainstay in the treatment of metastatic paragangliomas. This clinical scenario and discussion aim to enhance physicians' knowledge of the stepwise approach to treat these patients with paraganglioma-targeted radiotherapies. It comprehensively discusses current approaches to selecting paraganglioma patients for targeted radiotherapies and how to choose between the two radiotherapies based on specific patient and tumor characteristics, when either therapy is feasible, or one is superior to another. The safety, efficacy, toxicity profiles, and optimization of these radiotherapies are also discussed, along with other therapeutic options including radiotherapies, available for patients besides these two therapies. Perspectives in radiotherapies of paraganglioma patients are outlined since they hold promising approaches in the near future that can improve patient outcomes.

Safety and efficacy of multiple-dose versus single-dose MIBG therapy in patients with refractory pheochromocytoma and paraganglioma: a single-center retrospective analysis

OBJECTIVE

To investigate the incidence of adverse events (AEs) following single and multiple administrations of I-131 metaiodobenzylguanidine (MIBG) therapy for inoperable pheochromocytomas and paragangliomas (PPGLs).

METHODS

A single-center retrospective study was conducted on patients with inoperable PPGLs who underwent I-131 MIBG therapy between January 2000 and December 2020. A total of 28 patients with available electronic medical records were included. The treatment consisted of a single intravenous administration of 150 mCi (5.55 GBq) of I-131 MIBG. We evaluated the first MIBG treatment and repeated MIBG treatments performed within 200 days of the previous treatment. AEs for each treatment were evaluated using CTCAE version 4.0, and the statistical analysis was conducted at a significance level of p < 0.05. Objective response based on RECIST 1.1 criteria and biochemical response based on urinary catecholamines were assessed.

RESULTS

The study included a total of 63 administrations, consisting of 28 single administrations (SAs), including the first administration for all 28 cases, and 35 multiple administrations (MAs), which included the second or later administrations. Hematological AEs were evaluable for 23 SAs and 29 MAs. Grade 3 or higher leukopenia occurred in 9.8% of all administrations, and Grade 3 or higher lymphopenia in 23.5%; both were manageable through observation. There were no significant differences in clinical AE Grades 1-2 (p = 0.32), hematological AE Grades 1-2 (p = 0.22), or hematological AE Grades 3-4 (p = 0.12) between MAs and SAs. Statistical analysis for each type of AE revealed significant increases in leukopenia (p < 0.01) and lymphopenia (p = 0.04). No significant difference in anemia, thrombocytopenia, or neutropenia was observed between MAs and SAs. There was no significant increase in the incidence rate of Grade 3 or higher hematological AEs for any of the parameters. The objective response rate was 0% for SAs and 36% for MAs. Biochemical response rates were 18% for SAs and 67% for MAs.

CONCLUSION

In I-131 MIBG therapy for PPGLs, multiple administrations significantly increased only Grade 1 or 2 lymphopenia and leukopenia compared to single administration.

From FDG and beyond: the evolving potential of nuclear medicine

The radiopharmaceutical 2-[fluorine-18]fluoro-2-deoxy-D-glucose (FDG) has been dominantly used in positron emission tomography (PET) scans for over 20 years, and due to its vast utility its applications have expanded and are continuing to expand into oncology, neurology, cardiology, and infectious/inflammatory diseases. More recently, the addition of artificial intelligence (AI) has enhanced nuclear medicine diagnosis and imaging with FDG-PET, and new radiopharmaceuticals such as prostate-specific membrane antigen (PSMA) and fibroblast activation protein inhibitor (FAPI) have emerged. Nuclear medicine therapy using agents such as [177Lu]-dotatate surpasses conventional treatments in terms of efficacy and side effects. This article reviews recently established evidence of FDG and non-FDG drugs and anticipates the future trajectory of nuclear medicine.

Predictive Factors of Early 18F-Fluorodeoxyglucose-Positron Emission Tomography Response to [131I] Metaiodobenzylguanidine Treatment for Unresectable or Metastatic Pheochromocytomas and Paragangliomas

INTRODUCTION

Pheochromocytomas and paragangliomas (PPGLs) are rare neuroendocrine tumours that produce catecholamines. [131I] metaiodobenzylguanidine (MIBG)-avid unresectable or metastatic PPGLs are treated with [131I] MIBG radionuclide therapy. A high metabolic tumour volume (MTV) and total lesion glycolysis (TLG) can be poor prognostic factors. Therefore, we evaluated the metabolic responses to [131I] MIBG therapy with respect to other clinical factors.

METHODS

A retrospective study was performed on a series of 20 patients who underwent FDG-PET before and after [131I] MIBG therapy. We administered a single dose comprising 5.5 GBq of [131I] MIBG (usually three times; for some cases, the number was increased or decreased considering treatment efficacy and side effects). Semi-quantitative parameters (SUVmax, MTV, and TLG) were calculated using the liver SUV (mean + 3 × standard deviation) as a threshold on Metavol software. The semi-quantitative FDG-PET parameters for determining response were complete response (CR), partial remission (PR), stable disease (SD), and progressive disease (PD). We divided our study participants into the PD and non-PD groups (i.e., SD + PR + CR) and compared the overall survival (OS) between the two groups. Subsequently, we evaluated the relationships between metabolic response and age, sex, tumour type, metastatic site, chemotherapy or external radiation history, and 24-h urine catecholamine levels by univariate logistic regression analyses.

RESULTS

Both MTV-based and TLG-based criteria for PD versus non-PD were significant prognostic factors (p = 0.014). However, treatment response as evaluated based on the SUVmax was not a significant predictor. Higher urinary dopamine levels were associated with poor metabolic response as assessed by MTV and TLG (OR 1.002, p = 0.029). The other clinical parameters were non-significant.

CONCLUSION

Poor metabolic response (measured with MTV and TLG) to [131I] MIBG therapy in unresectable or metastatic PPGLs was related to shorter OS. The poor metabolic response can be predicted using the urinary dopamine level.

External Beam Radiotherapy in Advanced Pheochromocytoma and Paraganglioma: An Observation of a Rare Abscopal Effect

Metastatic pheochromocytoma and paraganglioma are incurable, and effective treatment of systemic symptoms resulting from catecholamine excess and local symptoms from tumor growth are crucial to prolong survival and improve quality of life. We report the first case of metastatic pheochromocytoma wherein external beam radiotherapy (EBRT) demonstrated efficacy in both target and nontarget lesions, demonstrating the "abscopal effect." EBRT reduced tumor volume and catecholamine secretion and improved catecholamine excess-related complications, including glycemic control. EBRT is an effective treatment option for metastatic pheochromocytoma and paraganglioma because of its minimal invasiveness, safety, and potential for the rare abscopal effect.