Response, survival, and long-term toxicity after therapy with the radiolabeled somatostatin analogue [90Y-DOTA]-TOC in metastasized neuroendocrine cancers

Sunitinib for the treatment of patients with advanced pheochromocytomas or paragangliomas: The phase 2 non-randomized SUTNET clinical trial

BACKGROUND

Metastatic Pheochromocytomas and paragangliomas (PPGLs) are rare neuroendocrine tumors characterized by high morbidity and limited systemic treatment options, mainly based on radiometabolic treatments or chemotherapy. Based on the preclinical rationale that PGGLs carcinogenesis relies on angiogenesis, treatment with tyrosine kinase inhibitors (TKI) may represent another viable therapeutic option.

METHODS

We conducted a prospective phase II study in patients with metastatic or unresectable PGGLs. Patients received sunitinib (50 mg daily for 4 weeks, followed by a 2-week rest period) until progressive disease (PD), unacceptable toxicity or consent withdrawal. The primary endpoint was 12-month progression-free survival (PFS) rate; secondary endpoints were safety overall response rate (ORR) according to RECIST 1.1 criteria and overall survival (OS). EudraCT Number: 2011-002632-99.

RESULTS

Fifty patients were included. At a median follow-up of 71.7 months (IQR 35.4-100.1), the 1 year-PFS rate was 53.4 % (95 %CI 41.1-69.3) and median PFS was 14.1 months (95 % CI 8.9-25.7). ORR was 15.6 %, the median OS was 49.4 months (95 %CI 21.2-NA), and grade 3 or higher treatment-related adverse events were reported in 34 % patients. No significant correlation was found between specific genetic alterations or genomic clusters and sunitinib efficacy.

CONCLUSION

Sunitinib is an active drug in patients with advanced PGGLs, capable of inducing prolonged disease control with a manageable toxicity profile.

Comparison of the tolerability of 161Tb- and 177Lu-labeled somatostatin analogues in the preclinical setting

PURPOSE

[177Lu]Lu-DOTATATE is an established somatostatin receptor (SSTR) agonist for the treatment of metastasized neuroendocrine neoplasms, while the SSTR antagonist [177Lu]Lu-DOTA-LM3 has only scarcely been employed in clinics. Impressive preclinical data obtained with [161Tb]Tb-DOTA-LM3 in tumor-bearing mice indicated the potential of terbium-161 as an alternative to lutetium-177. The aim of the present study was to compare the tolerability of 161Tb- and 177Lu-based DOTA-LM3 and DOTATATE in immunocompetent mice.

METHODS

Dosimetry calculations were performed based on biodistribution data of the radiopeptides in immunocompetent mice. Treatment-related effects on blood cell counts were assessed on Days 10, 28 and 56 after application of [161Tb]Tb-DOTA-LM3 or [161Tb]Tb-DOTATATE at 20 MBq per mouse. These radiopeptides were also applied at 100 MBq per mouse and the effects compared to those observed after application of the 177Lu-labeled counterparts. Bone marrow smears, blood plasma parameters and organ histology were assessed at the end of the study.

RESULTS

The absorbed organ dose was commonly higher for the SSTR antagonist than for the SSTR agonist and for terbium-161 over lutetium-177. Application of a therapeutic activity level of 20 MBq [161Tb]Tb-DOTA-LM3 or [161Tb]Tb-DOTATATE was well tolerated without major hematological changes. The injection of 100 MBq of the 161Tb- and 177Lu-based somatostatin analogues affected the blood cell counts, however. The lymphocytes were 40-50% lower in treated mice compared to the untreated controls on Day 10 irrespective of the radionuclide employed. At the same timepoint, thrombocyte and erythrocyte counts were 30-50% and 6-12% lower, respectively, after administration of the SSTR antagonist (p < 0.05) while changes were less pronounced in mice injected with the SSTR agonist. All blood cell counts were in the normal range on Day 56. Histological analyses revealed minimal abnormalities in the kidneys, liver and spleen of treated mice. No correlation was observed between the organ dose and frequency of the occurrence of abnormalities.

CONCLUSION

Hematologic changes were more pronounced in mice treated with the SSTR antagonist than in those treated with the SSTR agonist. Despite the increased absorbed dose delivered by terbium-161 over lutetium-177, [161Tb]Tb-DOTA-LM3 and [161Tb]Tb-DOTATATE should be safe at activity levels that are recommended for their respective 177Lu-based analogues.

Radioligand Therapy in Patients with Lung Neuroendocrine Tumors: A Systematic Review on Efficacy and Safety

Neuroendocrine neoplasms (NENs), arising from various sites, present therapeutic challenges. Radioligand therapy (RLT) is effective for unresectable/metastatic NENs with increased somatostatin receptor uptake. While evidence supports RLT's efficacy in midgut NETs, its role in lung NETs remains underexplored. Clinical guidelines place RLT as a third or fourth-line option in this setting. However, in the last years several studies investigated mainly retrospectively effectiveness and safety of RLT in lung NET. The aim of this review is to assess the efficacy and safety of RLT in patients with lung NETs. Following PRISMA guidelines, a systematic review of MEDLINE and EMBASE databases retrieved English articles until March 31, 2023. Inclusion criteria encompassed studies involving RLT in lung NETs with efficacy and safety assessments. Twenty-seven studies met the criteria, totaling 786 patients. The pooled analysis revealed a 25.6% objective response rate and 75.6% disease control rate. Median progression-free survival averaged 20 months, while overall survival averaged 45 months. Factors affecting response included tumor burden, prior treatments, 18F-FDG PET scan uptake, and histological variants. RLT exhibited manageable grade 1/2 adverse effects, predominantly hematological, with Lu177 demonstrating a more favorable profile than Y90. The findings support RLT's effectiveness in lung NETs, offering hope for advanced SSTR-positive patients. Although identifying predictive factors for response remains challenging, RLT retained efficacy even after prior therapies and typical carcinoids displayed a slightly better response than atypical ones. Prospective trials are imperative to establish RLT's definitive efficacy and its place in the therapeutic landscape for lung NETs.

Peptide Receptor Radionuclide Therapy of Neuroendocrine Tumors: Agonist, Antagonist and Alternatives

Peptide receptor radionuclide therapy (PRRT) today is a well-established treatment strategy for patients with neuroendocrine tumors (NET). First performed already more than 30 years ago, PRRT was incorporated only in recent years into the major oncology guidelines, based on its proven efficacy and safety in clinical trials. Following the phase 3 NETTER-1 trial, which led to the final registration of the radiopharmaceutical Luthatera® for G1/G2 NET patients in 2017, the long-term results of the phase 3 NETTER-2 trial may pave the way for a new treatment option also for advanced G2/G3 patients as first-line therapy. The growing knowledge about the synergistic effect of combined therapies could also allow alternative (re)treatment options for NET patients, in order to create a tailored treatment strategy. The evolving thera(g)nostic concept could be applied for the identification of patients who might benefit from different image-guided treatment strategies. In this scenario, the use of dual tracer PET/CT in NET patients, using both [18F]F-FDG/[68Ga]Ga-DOTA-somatostatin analog (SSA) for diagnosis and follow-up, is under discussion and could also result in a powerful prognostic tool. In addition, alternative strategies based on different metabolic pathways, radioisotopes, or combinations of different medical approaches could be applied. A number of different promising "doors" could thus open in the near future for the treatment of NET patients - and the "key" will be thera(g)nostic!

Clonal Hematopoiesis in Patients With Neuroendocrine Tumor Treated With Lutetium-177 and the Risk of Thrombocytopenia: A Prospective Study

PURPOSE

Thrombocytopenia is a relatively common dose-limiting toxicity during peptide receptor radionuclide therapy (PRRT) in patients with NET. Although uncommon, some patients develop persistent cytopenia and eventually therapy-related myeloid neoplasm (t-MN), which has a dismal prognosis. As the indications for PRRT are expanding, it is important to investigate factors that may predict cytopenias during/after PRRT. We prospectively evaluated the prevalence of clonal hematopoiesis (CH) and cytopenia in patients with NET undergoing PRRT.

MATERIALS AND METHODS

Patients with metastatic NET with plan to receive four cycles of lutetium-177 were enrolled. CH was evaluated before PRRT using a panel of 220 genes with a targeted depth of ≥1,000×. Patients were followed during PRRT and every 3 months thereafter.

RESULTS

Of 37 patients enrolled, the median age was 68 years and 51.4% were male. Previous treatment exposures included alkylating agents in 30%, platinum agents in 8%, and external radiation in 13%. CH was detected in 35.1% using a variant allele frequency (VAF) cutoff of ≥2% and 45.9% with a VAF of ≥1%. The most common mutations were in age-related genes (DNMT3A, TET2). CH was not associated with anemia or neutropenia; however, it was associated with lower platelet count at baseline and more time spent in a thrombocytopenic state during/after PRRT. Five patients had bone marrow biopsies (BMBs) because of sustained hematologic dysfunction post-PRRT, and of those, diagnoses included clonal cytopenia of undetermined significance (CCUS) in three and idiopathic cytopenia of undetermined significance (ICUS) in two.

CONCLUSION

CH is present in 35.1% of patients with NET and is associated with thrombocytopenia risk during PRRT. Future studies with long-term follow-up will delineate whether CH might be a predictor for higher risk of t-MN after PRRT.

Effectiveness and Safety of Retreatment with 177Lu-DOTATATE in Patients with Progressive Neuroendocrine Tumors: A Retrospective Real-World Study in the United States

Advanced neuroendocrine tumors (NETs) are associated with a poor prognosis. A regimen of 4 cycles of 177Lu-DOTATATE has been shown to improve both progression-free survival (PFS) and overall survival (OS) in patients with advanced NETs. To the best of our knowledge, this is the first study in the United States to evaluate the effectiveness and safety of additional cycles of 177Lu-DOTATATE therapy in patients with progressive NETs. Methods: This was a retrospective chart review of adults with advanced NETs. The patients had undergone initial treatment with up to 4 cycles of 177Lu-DOTATATE and, after disease progression and a period of at least 6 mo since the end of the initial treatment, were retreated with at least 1 additional cycle at a single center (2010-2020). Patient characteristics, treatment patterns, and clinical outcomes were evaluated descriptively. Response was evaluated according to RECIST 1.1; toxicity was defined using criteria from Common Terminology Criteria for Adverse Events, version 5.0. Kaplan-Meier plots were used to evaluate PFS and OS. Results: Of the 31 patients who received 177Lu-DOTATATE retreatment, 61% were male and 94% were White. Overall, patients received a median of 6 cycles (4 initial cycles and 2 retreatment cycles), and the mean administered activity was 41.9 GBq. Two patients also went on to receive additional retreatment (1 and 2 cycles, individually) after a second period of at least 6 mo and progression after retreatment. Best responses of partial response and stable disease were observed in 35% and 65% of patients after the initial treatment and 23% and 45% of patients after retreatment, respectively. The median PFS after the initial treatment was 20.2 mo and after retreatment was 9.6 mo. The median OS after the initial treatment was 42.6 mo and after retreatment was 12.6 mo. Hematologic parameters decreased significantly during both the initial treatment and retreatment but recovered such that there was little difference between the values before the initial treatment and before the retreatment. Clinically significant hematotoxicity occurred in 1 and 3 patients after the initial treatment and retreatment, respectively. No grade 3 or 4 nephrotoxicity was observed. Conclusion: Retreatment with 177Lu-DOTATATE after progression appeared to be well tolerated and offered disease control in patients with progressive NETs after initial 177Lu-DOTATATE treatment.

Radiolabeled Somatostatin Receptor Antagonist Versus Agonist for Peptide Receptor Radionuclide Therapy in Patients with Therapy-Resistant Meningioma: PROMENADE Phase 0 Study

Our primary aim was to compare the therapeutic index (tumor-to-bone marrow and tumor-to-kidney absorbed-dose ratios) of the new radiolabeled somatostatin receptor antagonist [177Lu]Lu-DOTA-JR11 with the established radiolabeled somatostatin receptor agonist [177Lu]Lu-DOTATOC in the same patients with progressive, standard therapy-refractory meningioma. Methods: In this prospective, single-center, open-label phase 0 study (NCT04997317), 6 consecutive patients were included: 3 men and 3 women (mean age, 63.5 y). Patients received 6.9-7.3 GBq (standard injected radioactivity) of [177Lu]Lu-DOTATOC followed by 3.3-4.9 GBq (2 GBq/m2 × body surface area) of [177Lu]Lu-DOTA-JR11 at an interval of 10 ± 1 wk. In total, 1 [177Lu]Lu-DOTATOC and 2-3 [177Lu]Lu-DOTA-JR11 treatment cycles were performed. Quantitative SPECT/CT was done at approximately 24, 48, and 168 h after injection of both radiopharmaceuticals to calculate meningioma and organ absorbed doses as well as tumor-to-organ absorbed-dose ratios (3-dimensional segmentation approach for meningioma, kidneys, liver, bone marrow, and spleen). Results: The median of the meningioma absorbed dose of 1 treatment cycle was 3.4 Gy (range, 0.8-10.2 Gy) for [177Lu]Lu-DOTATOC and 11.5 Gy (range, 4.7-22.7 Gy) for [177Lu]Lu-DOTA-JR11. The median bone marrow and kidney absorbed doses after 1 treatment cycle were 0.11 Gy (range, 0.05-0.17 Gy) and 2.7 Gy (range, 1.3-5.3 Gy) for [177Lu]Lu-DOTATOC and 0.29 Gy (range, 0.16-0.39 Gy) and 3.3 Gy (range, 1.6-5.9 Gy) for [177Lu]Lu-DOTA-JR11, resulting in a 1.4 (range, 0.9-1.9) times higher median tumor-to-bone marrow absorbed-dose ratio and a 2.9 (range, 2.0-4.8) times higher median tumor-to-kidney absorbed-dose ratio with [177Lu]Lu-DOTA-JR11. According to the Common Terminology Criteria for Adverse Events version 5.0, 2 patients developed reversible grade 2 lymphopenia after 1 cycle of [177Lu]Lu-DOTATOC. Afterward, 2 patients developed reversible grade 3 lymphopenia and 1 patient developed reversible grade 3 lymphopenia and neutropenia after 2-3 cycles of [177Lu]Lu-DOTA-JR11. No grade 4 or 5 adverse events were observed at 15 mo or more after the start of therapy. The disease control rate was 83% (95% CI, 53%-100%) at 12 mo or more after inclusion. Conclusion: Treatment with 1 cycle of [177Lu]Lu-DOTA-JR11 showed 2.2-5.7 times higher meningioma absorbed doses and a favorable therapeutic index compared with [177Lu]Lu-DOTATOC after injection of 1.4-2.1 times lower activities. The first efficacy results demonstrated a high disease control rate with an acceptable safety profile in the standard therapy for refractory meningioma patients. Therefore, larger studies with [177Lu]Lu-DOTA-JR11 are warranted in meningioma patients.

Effects of Peptide Receptor Radiotherapy in Patients with Advanced Paraganglioma and Pheochromocytoma: A Nation-Wide Cohort Study

INTRODUCTION

Pheochromocytomas and paragangliomas are rare neuroendocrine tumours that originate from chromaffin cells within the adrenal medulla or extra-adrenal sympathetic ganglia. Management of disseminated or metastatic pheochromocytomas and paragangliomas continues to pose challenges and relies on limited evidence.

METHOD

In this study, we report retrospective data on median overall survival (OS) and median progression-free survival (PFS) for all Danish patients treated with peptide receptor radionuclide therapy (PRRT) with 177Lu-Dotatate or 90Y-Dotatate over the past 15 years. One standard treatment of PRRT consisted of 4 consecutive cycles with 8-14-week intervals.

RESULTS

We included 28 patients; 10 were diagnosed with pheochromocytoma and 18 with paraganglioma. Median age at first PRRT was 47 (IQR 15-76) years. The median follow-up time was 31 (IQR 17-37) months. Eight patients died during follow-up. Median OS was 72 months, and 5-year survival was 65% with no difference between pheochromocytoma and paraganglioma. Patients with germline mutations had better survival than patients without mutations (p = 0.041). Median PFS after the first cycle of PRRT was 30 months. For patients who previously received systemic treatment, the median PFS was 19 months, compared with 32 months for patients with no previous systemic treatment (p = 0.083).

CONCLUSIONS

The median OS of around 6 years and median PFS of around 2.5 years found in this study are comparable to those reported in previous studies employing PRRT. Based on historical data, the efficacy of PRRT may be superior to 131I-MIBG therapy, and targeted therapy with sunitinib and PRRT might therefore be considered as first-line treatment in this patient group.

Sunitinib for metastatic progressive phaeochromocytomas and paragangliomas: results from FIRSTMAPPP, an academic, multicentre, international, randomised, placebo-controlled, double-blind, phase 2 trial

BACKGROUND

No randomised controlled trial has ever been done in patients with metastatic phaeochromocytomas and paragangliomas. Preclinical and first clinical evidence suggested beneficial effects of sunitinib. We aimed to evaluate the safety and efficacy of sunitinib in patients with metastatic phaeochromocytomas and paragangliomas.

METHODS

FIRSTMAPPP is a multicentre, international, randomised, placebo-controlled, double-blind, phase 2 trial done at 14 academic centres across four European countries. Eligible participants were adults (aged ≥18 years) with sporadic or inherited progressive metastatic phaeochromocytomas and paragangliomas. Patients were randomly assigned (1:1) to receive either oral sunitinib (37·5 mg per day) or placebo. Randomisation was stratified according to SDHB status (mutation present vs wild type) and number of previous systemic therapies (0 vs ≥1). Primary endpoint was the rate of progression-free survival at 12 months according to real-time central review (Response Evaluation Criteria in Solid Tumours version 1.1). On the basis of a two-step Simon model, we aimed for the accrual of 78 patients, assuming a 20% improvement of the 12-month progression-free survival rate from 20% to 40%, to conclude that sunitinib is effective. Crossover from the placebo group was allowed. This trial is registered with ClinicalTrials.gov, number NCT01371201, and is closed for enrolment.

FINDINGS

From Dec 1, 2011, to Jan 31, 2019, a total of 78 patients with progressive metastatic phaeochromocytomas and paragangliomas were enrolled (39 patients per group). 25 (32%) of 78 patients had germline SDHx variants and 54 (69%) had used previous therapies. The primary endpoint was met, with a 12-month progression-free survival in 14 of 39 patients (36% [90% CI 23-50]) in the sunitinib group. In the placebo group, the 12-month progression-free survival in seven of 39 patients was 19% (90% CI 11-31), validating the hypotheses of our study design. The most frequent grade 3 or 4 adverse events were asthenia (seven [18%] of 39 and one [3%] of 39), hypertension (five [13%] and four [10%]), and back or bone pain (one [3%] and three [8%]) in the sunitinib and placebo groups, respectively. Three deaths occurred in the sunitinib group: these deaths were due to respiratory insufficiency, amyotrophic lateral sclerosis, and rectal bleeding. Only the latter event was considered drug related. Two deaths occurred in the placebo group due to aspiration pneumonia and septic shock.

INTERPRETATION

This first randomised trial supports the use of sunitinib as the medical option with the highest level of evidence for anti-tumour efficacy in progressive metastatic phaeochromocytomas and paragangliomas.

FUNDING

French Ministry of Health, through the National Institute for Cancer, German Ministry of Education and Research, and the German Research Foundation within the CRC/Transregio 205/2, EU Seventh Framework Programme, and a private donator grant.

Towards Effective Targeted Alpha Therapy for Neuroendocrine Tumours: A Review

This review article explores the evolving landscape of Molecular Radiotherapy (MRT), emphasizing Peptide Receptor Radionuclide Therapy (PRRT) for neuroendocrine tumours (NETs). The primary focus is on the transition from β-emitting radiopharmaceuticals to α-emitting agents in PRRT, offering a critical analysis of the radiobiological basis, clinical applications, and ongoing developments in Targeted Alpha Therapy (TAT). Through an extensive literature review, the article delves into the mechanisms and effectiveness of PRRT in targeting somatostatin subtype 2 receptors, highlighting both its successes and limitations. The discussion extends to the emerging paradigm of TAT, underlining its higher potency and specificity with α-particle emissions, which promise enhanced therapeutic efficacy and reduced toxicity. The review critically evaluates preclinical and clinical data, emphasizing the need for standardised dosimetry and a deeper understanding of the dose-response relationship in TAT. The review concludes by underscoring the significant potential of TAT in treating SSTR2-overexpressing cancers, especially in patients refractory to β-PRRT, while also acknowledging the current challenges and the necessity for further research to optimize treatment protocols.

Sequencing of Somatostatin-Receptor-Based Therapies in Neuroendocrine Tumor Patients

Most well-differentiated neuroendocrine tumors (NETs) express high levels of somatostatin receptors, particularly subtypes 2 and 5. Somatostatin analogs (SSAs) bind to somatostatin receptors and are used for palliation of hormonal syndromes and control of tumor growth. The long-acting SSAs octreotide long-acting release and lanreotide are commonly used in the first-line metastatic setting because of their tolerable side effect profile. Radiolabeled SSAs are used both for imaging and for treatment of NETs. 177Lu-DOTATATE is a β-emitting radiolabeled SSA that has been proven to significantly improve progression-free survival among patients with progressive midgut NETs and is approved for treatment of metastatic gastroenteropancreatic NETs. A key question in management of patients with gastroenteropancreatic and lung NETs is the sequencing of 177Lu-DOTATATE in relation to other systemic treatments (such as everolimus) or liver-directed therapies. This question is particularly complicated given the heterogeneity of NETs and the near absence of randomized trials comparing active treatment options. This state-of-the-art review examines the evidence supporting use of somatostatin-receptor-targeted treatments within the larger landscape of NET therapy and offers insights regarding optimal patient selection, assessment of benefit versus risk, and treatment sequencing.

Safety and efficacy of peptide receptor radionuclide therapy in patients with advanced pheochromocytoma and paraganglioma: A single-institution experience and review of the literature

INTRODUCTION

Despite advances in diagnosis and management, patients with advanced pheochromocytomas and paragangliomas (PPGL) face limited treatment options. This study aims to evaluate the safety and efficacy of peptide receptor radionuclide therapy (PRRT) in patients with advanced PPGL, based on a single-institution experience and provide a comprehensive review of the literature.

METHODS

A retrospective analysis was conducted on patients with advanced pheochromocytoma and paraganglioma who received PRRT at a single institution from April 2012 to March 2022. Clinical characteristics, treatment response, adverse events, and survival outcomes were assessed. A systematic literature review was also performed.

RESULTS

A total of 15 patients with advanced PPGL were included, the majority of whom had both metastatic and functional disease. Most patients received four infusions of 177Lu-DOTATATE (73%). The median therapeutic 177Lu-DOTATATE radioactivity for each infusion was 7.4 GBq. Only one patient was treated with one infusion of 90Y-DOTATATE (4.2 GBq) in addition to three infusions of Lu-177 DOTATATE. Overall, PRRT suggests a promising efficacy with disease control rate of 63.6% by RECIST v1.1. The median overall survival (OS) was not reached and the median progression free survival (PFS) was 25.9 months. In terms of safety, PRRT was well tolerated. Review of the literature revealed consistent findings, supporting the efficacy and safety of PRRT in PPGL.

CONCLUSION

This study suggests that PRRT is a safe and effective therapeutic option for patients with PPGL. Our findings align with the existing literature, providing additional evidence to support the use of PRRT in this challenging patient population.

Targeted radionuclide therapy in endocrine-related cancers: advances in the last decade

Targeted radionuclide therapy plays an increasingly important role in managing endocrine-related tumors and significantly advances the therapeutic landscape for patients with these diseases. With increasing FDA-approved therapies and advances in the field, come an increased knowledge of the potential for long-term toxicities associated with these therapies and the field must develop new strategies to increase potency and efficacy while individualizing the selection of patients to those most likely to respond to treatment. Novel agents and modalities of therapy are also being explored. This review will discuss the current landscape and describe the avenues for growth in the field currently being explored.

Lung Carcinoids: A Comprehensive Review for Clinicians

Lung carcinoids are neuroendocrine tumors, categorized as typical or atypical carcinoids based on their histological appearance. While most of these tumors are slow-growing neoplasms, they still possess malignant potential. Many patients are diagnosed incidentally on chest X-rays or CT scans. Presenting symptoms include cough, hemoptysis, wheezing, dyspnea, and recurrent pneumonia. Endocrine symptoms, such as carcinoid syndrome or ectopic Cushing's syndrome, are rare. Surgery is the primary treatment and should be considered in all patients with localized disease, even when thoracic lymph node metastases are present. Patients with distant metastases may be treated with somatostatin analogues, chemotherapy, preferably temozolomide-based, mTOR inhibitors, or peptide receptor radionuclide therapy (PRRT) with 177Lu-DOTATATE. Most patients have an excellent prognosis. Poor prognostic factors include atypical histology and lymph node metastases at diagnosis. Long-term follow-up is mandatory since metastases may occur late.

Theranostic Nuclear Medicine with Gallium-68, Lutetium-177, Copper-64/67, Actinium-225, and Lead-212/203 Radionuclides

Molecular changes in malignant tissue can lead to an increase in the expression levels of various proteins or receptors that can be used to target the disease. In oncology, diagnostic imaging and radiotherapy of tumors is possible by attaching an appropriate radionuclide to molecules that selectively bind to these target proteins. The term "theranostics" describes the use of a diagnostic tool to predict the efficacy of a therapeutic option. Molecules radiolabeled with γ-emitting or β+-emitting radionuclides can be used for diagnostic imaging using single photon emission computed tomography or positron emission tomography. Radionuclide therapy of disease sites is possible with either α-, β-, or Auger-emitting radionuclides that induce irreversible damage to DNA. This Focus Review centers on the chemistry of theranostic approaches using metal radionuclides for imaging and therapy. The use of tracers that contain β+-emitting gallium-68 and β-emitting lutetium-177 will be discussed in the context of agents in clinical use for the diagnostic imaging and therapy of neuroendocrine tumors and prostate cancer. A particular emphasis is then placed on the chemistry involved in the development of theranostic approaches that use copper-64 for imaging and copper-67 for therapy with functionalized sarcophagine cage amine ligands. Targeted therapy with radionuclides that emit α particles has potential to be of particular use in late-stage disease where there are limited options, and the role of actinium-225 and lead-212 in this area is also discussed. Finally, we highlight the challenges that impede further adoption of radiotheranostic concepts while highlighting exciting opportunities and prospects.

Novel Therapeutic Strategies Exploiting the Unique Properties of Neuroendocrine Neoplasms

BACKGROUND

Over the last few decades of treatment, the outcomes for at least some subsets of neuroendocrine neoplasms (NENs) have improved. However, the identification of new vulnerabilities for this heterogeneous group of cancers remains a priority.

METHODS

Using two libraries of compounds selected for potential repurposing, we identified the inhibitors of nicotinamide phosphoribosyltransferase (NAMPT) and histone deacetylases (HDAC) as the agents with the highest activity. We validated the hits in an expanded set of neuroendocrine cell lines and examined the mechanisms of action.

RESULTS

In Kelly, NH-6, and NCI-H82, which are two neuroblastoma and one small cell lung cancer cell lines, respectively, metabolic studies suggested that cell death following NAMPT inhibition is the result of a reduction in basal oxidative phosphorylation and energy production. NAMPT is the rate-limiting enzyme in the production of NAD+, and in the three cell lines, NAMPT inhibition led to a marked reduction in the ATP and NAD+ levels and the catalytic activity of the citric acid cycle. Moreover, comparative analysis of the mRNA expression in drug-sensitive and -insensitive cell lines found less dependency of the latter on oxidative phosphorylation for their energy requirement. Further, the analysis of HDAC and NAMPT inhibitors administered in combination found marked activity using low sub-lethal concentrations of both agents, suggesting a synergistic effect.

CONCLUSION

These data suggest NAMPT inhibitors alone or in combination with HDAC inhibitors could be particularly effective in the treatment of neuroendocrine neoplasms.

Image-Guided Precision Medicine in the Diagnosis and Treatment of Pheochromocytomas and Paragangliomas

In this comprehensive review, we aimed to discuss the current state-of-the-art medical imaging for pheochromocytomas and paragangliomas (PPGLs) diagnosis and treatment. Despite major medical improvements, PPGLs, as with other neuroendocrine tumors (NETs), leave clinicians facing several challenges; their inherent particularities and their diagnosis and treatment pose several challenges for clinicians due to their inherent complexity, and they require management by multidisciplinary teams. The conventional concepts of medical imaging are currently undergoing a paradigm shift, thanks to developments in radiomic and metabolic imaging. However, despite active research, clinical relevance of these new parameters remains unclear, and further multicentric studies are needed in order to validate and increase widespread use and integration in clinical routine. Use of AI in PPGLs may detect changes in tumor phenotype that precede classical medical imaging biomarkers, such as shape, texture, and size. Since PPGLs are rare, slow-growing, and heterogeneous, multicentric collaboration will be necessary to have enough data in order to develop new PPGL biomarkers. In this nonsystematic review, our aim is to present an exhaustive pedagogical tool based on real-world cases, dedicated to physicians dealing with PPGLs, augmented by perspectives of artificial intelligence and big data.

Metastatic Pheochromocytoma and Paraganglioma: Somatostatin Receptor 2 Expression, Genetics, and Therapeutic Responses

CONTEXT

Pheochromocytomas and paragangliomas (PPGLs) with pathogenic mutations in the succinate dehydrogenase subunit B (SDHB) are associated with a high metastatic risk. Somatostatin receptor 2 (SSTR2)-dependent imaging is the most sensitive imaging modality for SDHB-related PPGLs, suggesting that SSTR2 expression is a significant cell surface therapeutic biomarker of such tumors.

OBJECTIVE

Exploration of the relationship between SSTR2 immunoreactivity and SDHB immunoreactivity, mutational status, and clinical behavior of PPGLs. Evaluation of SSTR-based therapies in metastatic PPGLs.

METHODS

Retrospective analysis of a multicenter cohort of PPGLs at 6 specialized Endocrine Tumor Centers in Germany, The Netherlands, and Switzerland. Patients with PPGLs participating in the ENSAT registry were included. Clinical data were extracted from medical records, and immunohistochemistry (IHC) for SDHB and SSTR2 was performed in patients with available tumor tissue. Immunoreactivity of SSTR2 was investigated using Volante scores. The main outcome measure was the association of SSTR2 IHC positivity with genetic and clinical-pathological features of PPGLs.

RESULTS

Of 202 patients with PPGLs, 50% were SSTR2 positive. SSTR2 positivity was significantly associated with SDHB- and SDHx-related PPGLs, with the strongest SSTR2 staining intensity in SDHB-related PPGLs (P = .01). Moreover, SSTR2 expression was significantly associated with metastatic disease independent of SDHB/SDHx mutation status (P < .001). In metastatic PPGLs, the disease control rate with first-line SSTR-based radionuclide therapy was 67% (n = 22, n = 11 SDHx), and with first-line "cold" somatostatin analogs 100% (n = 6, n = 3 SDHx).

CONCLUSION

SSTR2 expression was independently associated with SDHB/SDHx mutations and metastatic disease. We confirm a high disease control rate of somatostatin receptor-based therapies in metastatic PPGLs.

Metastatic paraganglioma presenting with spinal cord compression requiring urgent surgery

We report a rare case of a functional bladder paraganglioma diagnosed in a young man who presented with acute compressive thoracic myelopathy secondary to vertebral metastasis. A histological diagnosis of a metastatic paraganglioma was made following biopsy of a rib lesion. CT revealed a lesion in the inferior wall of the bladder, which demonstrated avid uptake on 68Ga-DOTATATE PET/CT. Serum metanephrine levels were more than 40 times the upper limit of normal. The patient was hypertensive and treatment with doxazosin was initiated. In view of neurological deterioration, he required urgent spinal decompression to preserve neurological function and prevent permanent paraplegia. Despite inadequate alpha-blockade, surgery was successful, and the perioperative course was uneventful. Alpha-blockade was subsequently optimised. Treatment with cyclophosphamide, vincristine and dacarbazine was started but, in view of disease progression, treatment was subsequently changed to sunitinib.

Bronchial carcinoid tumors in children and adolescents - A report and management considerations from the German MET studies

OBJECTIVES

Bronchial carcinoid tumors (BC) are exceptionally rare in childhood, with an incidence of <0.2/1,000,000 per year. Typical low-grade BCs are distinguished from atypical, intermediate-grade BCs. Little is known about BCs in pediatric patients and management guidelines are missing. In this study, we explored characteristics and outcome of pediatric patients with BC prospectively registered with the Malignant Endocrine Tumor studies.

MATERIAL AND METHODS

We performed a retrospective multicenter study in children, adolescents, and young adults (aged 0-20 years) with BC reported to the German MET registry between January 1997 and December 2022. Data were last updated on 28 of February 2023.

RESULTS

Thirty-two patients were diagnosed at a median age of 15.0 years (range, 9.8-19.2). Atypical BCs (23.3%) were less frequent than typical, but more common than in adulthood. Lymph node metastases were present in 14.3% of cases (atypical BC: 28.6%, typical BC: 10.5%), distant metastases in one (3.1%) patient with atypical BC. 92.6% of patients were in complete remission after surgical resection (median follow-up: 2.7 years). The patient with metastatic spread and one patient with atypical BC and multiple recurrences were on treatment at last follow-up. 5-year event-free survival of typical BC was 100% and 83.3% in atypical BC.

CONCLUSIONS

Completely resected localized BCs in pediatric patients have a favorable outcome also with lung tissue sparing surgery. Atypical BC with risk of metastatic spread and recurrence occurred more frequently compared to adults. Interdisciplinary management and collaborative efforts are needed to improve our understanding and the management of pediatric BC.

A Comprehensive Review on Neuroendocrine Neoplasms: Presentation, Pathophysiology and Management

Neuroendocrine neoplasms (NENs) are a group of heterogeneous tumors with neuroendocrine differentiation that can arise from any organ. They account for 2% of all malignancies in the United States. A significant proportion of NEN patients experience endocrine imbalances consequent to increased amine or peptide hormone secretion, impacting their quality of life and prognosis. Over the last decade, pathologic categorization, diagnostic techniques and therapeutic choices for NENs-both well-differentiated neuroendocrine tumors (NETs) and poorly differentiated neuroendocrine carcinomas (NECs)-have appreciably evolved. Diagnosis of NEN mostly follows a suspicion from clinical features or incidental imaging findings. Hormonal or non-hormonal biomarkers (like serum serotonin, urine 5-HIAA, gastrin and VIP) and histology of a suspected NEN is, therefore, critical for both confirmation of the diagnosis and classification as an NET or NEC. Therapy for NENs has progressed recently based on a better molecular understanding, including the involvement of mTOR, VEGF and peptide receptor radionuclide therapy (PRRT), which add to the growing evidence supporting the possibility of treatment beyond complete resection. As the incidence of NENs is on the rise in the United States and several other countries, physicians are more likely to see these cases, and their better understanding may support earlier diagnosis and tailoring treatment to the patient. We have compiled clinically significant evidence for NENs, including relevant changes to clinical practice that have greatly updated our diagnostic and therapeutic approach for NEN patients.

[212Pb]Pb-eSOMA-01: A Promising Radioligand for Targeted Alpha Therapy of Neuroendocrine Tumors

Peptide receptor radionuclide therapy (PRRT) has been applied to the treatment of neuroendocrine tumors (NETs) for over two decades. However, improvement is still needed, and targeted alpha therapy (TAT) with alpha emitters such as lead-212 (²¹²Pb) represents a promising avenue. A series of ligands based on octreotate was developed. Lead-203 was used as an imaging surrogate for the selection of the best candidate for the studies with lead-212. ^203/212Pb radiolabeling and in vitro assays were carried out, followed by SPECT/CT imaging and ex vivo biodistribution in NCI-H69 tumor-bearing mice. High radiochemical yields (≥99%) and purity (≥96%) were obtained for all ligands. [²⁰³Pb]Pb-eSOMA-01 and [²⁰³Pb]Pb-eSOMA-02 showed high stability in PBS and mouse serum up to 24 h, whereas [²⁰³Pb]Pb-eSOMA-03 was unstable in those conditions. All compounds exhibited a nanomolar affinity (2.5-3.1 nM) for SSTR2. SPECT/CT images revealed high tumor uptake at 1, 4, and 24 h post-injection of [²⁰³Pb]Pb-eSOMA-01/02. Ex vivo biodistribution studies confirmed that the highest uptake in tumors was observed with [²¹²Pb]Pb-eSOMA-01. [²¹²Pb]Pb-eESOMA-01 displayed the highest absorbed dose in the tumor (35.49 Gy/MBq) and the lowest absorbed dose in the kidneys (121.73 Gy/MBq) among the three tested radioligands. [²¹²Pb]Pb-eSOMA-01 is a promising candidate for targeted alpha therapy of NETs. Further investigations are required to confirm its potential.

Peptide receptor radionuclide therapy in advanced Pheochromocytomas and Paragangliomas: a systematic review and meta-analysis

Objective

Peptide receptor radionuclide therapy (PRRT) for advanced pheochromocytomas and paragangliomas (PPGLs) has received increasing attention. The purpose of this article is to evaluate the efficacy and safety of PRRT in patients with metastatic or inoperable PPGLs by meta-analysis.

Methods

A literature search was conducted in PubMed, Embase, Scopus, and Cochrane Library databases up to November 2022. All articles on PRRT for PPGLs were searched, and appropriate data were included for analysis. The measures evaluated included objective response rate (ORR), disease control rate (DCR), clinical response rate, biochemical response rate, progression-free survival (PFS), overall survival (OS), and adverse events. Statistical analysis was performed using Stata 16.0 and the R programming language, data were combined using a random-effects model, and the results were presented using forest plots.

Results

A total of 20 studies with 330 patients were included in the analysis. The results showed that ORR and DCR were 20.0% (95% CI: 12.0%-28.0%) and 90.0% (95% CI: 85.0%-95.0%), respectively. Clinical and biochemical responses were 74.9% (95% CI: 56.3%-90.2%) and 69.5% (95%CI: 40.2%-92.9%). Median PFS and median OS were 31.79 (95% CI:21.25-42.33) months and 74.30 (95% CI: 0.75-147.84) months, respectively. Any grade of hematotoxicity and nephrotoxicity occurred in 22.3% (95% CI:12.5%-33.5%) and 4.3% (95% CI:0.2%-11.4%) patients. Grade 3-4 hemotoxicity occurred in 4.3% (95% CI:0.2%-11.4%) and grade 3-4 nephrotoxicity in 4/212 patients. Additionally, Treatment was discontinued in 9.0% (95% CI: 0.5%-23.3%) patients and one patient died as a result of a toxicity.

Conclusion

Patients with metastatic or inoperable PPGLs can be effectively treated with PRRT, and it has a favorable safety profile.

Systematic review registration

https://www.crd.york.ac.uk/PROSPERO, identifier CRD42022359232.

Efficacy of [177Lu]Lu-DOTATATE in metastatic neuroendocrine neoplasms of different locations: data from the SEPTRALU study

BACKGROUND

Peptide receptor radionuclide therapy (PRRT) is one of the most promising therapeutic strategies in neuroendocrine neoplasms (NENs). Nevertheless, its role in certain tumor sites remains unclear. This study sought to elucidate the efficacy and safety of [177Lu]Lu-DOTATATE in NENs with different locations and evaluate the effect of the tumor origin, bearing in mind other prognostic variables. Advanced NENs overexpressing somatostatin receptors (SSTRs) on functional imaging, of any grade or location, treated at 24 centers were enrolled. The protocol consisted of four cycles of 177Lu-DOTATATE 7.4 GBq iv every 8 weeks (NCT04949282).

RESULTS

The sample comprised 522 subjects with pancreatic (35%), midgut (28%), bronchopulmonary (11%), pheochromocytoma/ paraganglioma (PPGL) (6%), other gastroenteropancreatic (GEP) (11%), and other non-gastroenteropancreatic (NGEP) (9%) NENs. The best RECIST 1.1 responses were complete response, 0.7%; partial response, 33.2%; stable disease, 52.1%; and tumor progression, 14%, with activity conditioned by the tumor subtype, but with benefit in all strata. Median progression-free survival (PFS) was 31.3 months (95% CI, 25.7-not reached [NR]) in midgut, 30.6 months (14.4-NR) in PPGL, 24.3 months (18.0-NR) in other GEP, 20.5 months (11.8-NR) in other NGEP, 19.8 months (16.8-28.1) in pancreatic, and 17.6 months (14.4-33.1) in bronchopulmonary NENs. [177Lu]Lu-DOTATATE exhibited scant severe toxicity.

CONCLUSION

This study confirms the efficacy and safety of [177Lu]Lu-DOTATATE in a wide range of SSTR-expressing NENs, regardless of location, with clinical benefit and superimposable survival outcomes between pNENs and other GEP and NGEP tumor subtypes different from midgut NENs.

A dosimetric comparison of systemic peptide receptor radionuclide therapy and intra-arterial peptide receptor radionuclide therapy in patients with liver dominant gastroenteropancreatic neuroendocrine tumours

OBJECTIVES

Intra-arterial radionuclide therapy (IART) treatment allows direct delivery of 177 Lu-DOTATATE to the overexpressed somatostatin-positive neuroendocrine liver metastases, which led to higher tumour concentration compared with systemic radionuclide therapy (SRT). The aim was to evaluate and compare the absorbed doses of both IART and SRT to organs and hepatic metastatic sites.

METHODS

A total of 48 patients received SRT and IART. In SRT, activity was administered intravenously, whereas in IART, activity was administered directly into hepatic arteries. The sequential whole-body images were acquired at 2, 4, 24, 72 and 160 h. The reconstructed whole-body planar and single-photon emission computed tomography-computed tomography images were processed using the Dosimetry Toolkit for the estimation of normalized cumulated activity in the organs and tumour lesions. The absorbed dose was computed using OLINDA EXM 2.0 software.

RESULTS

The median absorbed dose (mGy/MBq) of kidneys and spleen in IART was compared with SRT and found to be decreased by 30.7% ( P  = 0.03) and 37.5% ( P  = 0.08), whereas it was found to be increased by 40% ( P  = 0.26) and 8.1% ( P  = 0.28) in the liver and lungs. The median dose (mGy/MBq) of tumours determined in IART was found to be increased by 62.2% ( P  = 0.04).

CONCLUSION

IART with 177 Lu-DOTATATE significantly increases tumour dose while reducing overall systemic toxicity in comparison to SRT treatment. After considering the maximum tolerance limit of kidneys in peptide receptor radionuclide therapy, the number of treatment cycles and injected activity can be optimized further with IART for better response and survival.

Recent Advances in Radiopharmaceutical Theranostics of Pheochromocytoma and Paraganglioma

As a rare kind of non-epithelial neuroendocrine neoplasms, paragangliomas (PGLs) exhibit various clinical characteristics with excessive catecholamine secretion and have been a research focus in recent years. Although several modalities are available nowadays, radiopharmaceuticals play an integral role in the management of PGLs. Theranostics utilises radiopharmaceuticals for diagnostic and therapeutic intentions by aiming at a specific target in tumour and has been considered a possible means in diagnosis, staging, monitoring and treatment planning. Numerous radiopharmaceuticals have been developed over the past decades. 123/131-Metaiodobenzylguanidine (123/131I-MIBG), the theranostics pair target on norepinephrine transporter system, has remained a fantastic protocol for patients with PGLs because of disease control with limited toxicity. The high-specific-activity 131I-MIBG was authorised by the Food and Drug Administration as a systemic treatment method for metastatic PGLs in 2018. Afterward, peptide receptor radionuclide therapy, which uses radiolabelled somatostatin (SST) analogues, has been exploited as a superior substitute. 68Ga-somatostatin analogue (SSA) PET showed significant performance in diagnosing PGLs than MIBG scintigraphy, especially in patients with head and neck PGLs or SDHx mutation. 90Y/177Lu-DOTA-SSA is highly successful and has preserved favourable safety with mounting evidence regarding objective response, disease stabilisation, symptomatic and hormonal management and quality of life preservation. Besides the ordinary beta emitters, alpha-emitters such as 211At-MABG and 225Ac-DOTATATE have been investigated intensively in recent years. However, many studies are still in the pre-clinical stage, and more research is necessary. This review summarises the developments and recent advances in radiopharmaceutical theranostics of PGLs.

An Engineered Probiotic Platform for Cancer Epitope-Independent Targeted Radionuclide Therapy of Solid Tumors

Targeted radionuclide therapy (TRT) is an emerging therapeutic modality for the treatment of various solid cancers. Current approaches rely on the presence of cancer-specific epitopes and receptors against which a radiolabeled ligand is systemically administered to specifically deliver cytotoxic doses of α and β particles to tumors. In this proof-of-concept study, tumor-colonizing Escherichia coli Nissle 1917 (EcN) is utilized to deliver a bacteria-specific radiopharmaceutical to solid tumors in a cancer-epitope independent manner. In this microbe-based pretargeted approach, the siderophore-mediated metal uptake pathway is leveraged to selectively concentrate copper radioisotopes, 64 Cu and 67 Cu, complexed to yersiniabactin (YbT) in the genetically modified bacteria. 64 Cu-YbT facilitates positron emission tomography (PET) imaging of the intratumoral bacteria, whereas 67 Cu-YbT delivers a cytotoxic dose to the surrounding cancer cells. PET imaging with 64 Cu-YbT reveals persistence and sustained growth of the bioengineered microbes in the tumor microenvironment. Survival studies with 67 Cu-YbT reveals significant attenuation of tumor growth and extends survival of both MC38 and 4T1  tumor-bearing mice harboring the microbes. Tumor response to this pretargeted approach correlates with promising anti-tumor immunity, with noticeable CD8+ T:Treg cell ratio. Their strategy offers a pathway to target and ablate multiple solid tumors independent of their epitope and receptor phenotype.

Molecular imaging Theranostics of Neuroendocrine Tumors

Neuroendocrine neoplasms (NEN) are rare and heterogeneous tumors, originating mostly from the gastro-entero-pancreatic (GEP) tract followed by the lungs. Multidisciplinary discussion is mandatory for optimal diagnostic and therapeutic management. Well-differentiated NEN (NET) present a high expression of somatostatin receptors (SSTR) and can be studied with [68Ga]-DOTA-peptides ([68Ga]Ga-DOTANOC, [68Ga]Ga-DOTATOC, [68Ga]Ga-DOTATATE) PET/CT to assess disease extension and the eligibility for peptide receptor radionuclide therapy (PRRT). SSTR-analogues labelled with 90Y or 177Lu have been used since mid-90s for NET therapy. PRRT is now considered an effective and safe treatment option for SSTR-expressing NET: following the approval of 177Lu-DOTATATE by FDA and EMA, PRRT is now part of the therapeutic algorithms of the main scientific societies. New strategies to improve PRRT efficacy and to reduce its toxicity are under evaluation (eg, personalization of treatment schemes, the selection of the most suitable patients, improvement of response assessment criteria, optimization of treatment sequencing, feasibility of PRRT-retreatment, combination of PRRT with other treatments options). Recently, several emerging radiopharmaceuticals showed encouraging results for both imaging and therapy (eg, SSTR-analogues labelled with 18F, SSTR-antagonists for both diagnosis and therapy, alpha-labelling for therapy, radiopharmaceuticals binding to new cellular targets). Aim of this review is to focus on current knowledge and to outline emerging perspectives for NEN's diagnosis and therapy.

Non-invasive estimation of split renal function from routine 68Ga-SSR-PET/CT scans

Objective

Patients with impaired kidney function are at elevated risk for nephrotoxicity and hematotoxicity from peptide receptor radionuclide therapy (PPRT) for advanced neuroendocrine tumors. Somatostatin receptor (SSR)-PET/CT imaging is the method of choice to identify sufficient SSR expression as a prerequisite for PRRT. Therefore, our study aimed to explore whether split renal function could be evaluated using imaging data from routine SSR-PET/CT prior to PRRT.

Methods

In total, 25 consecutive patients who underwent SSR-PET/CT (Siemens Biograph mCT^®) before PRRT between June 2019 and December 2020 were enrolled in this retrospective study. PET acquisition in the caudocranial direction started at 20 ± 0.5 min after an i.v. injection of 173 ± 20 MBq [⁶⁸Ga]Ga-ha DOTATATE, and the kidneys were scanned at 32 ± 0.5 min p.i. The renal parenchyma was segmented semi-automatically using an SUV-based isocontour (SUV between 5 and 15). Multiple parameters including SUVmean of renal parenchyma and blood pool, as well as parenchyma volume, were extracted, and accumulation index (ACI: renal parenchyma volume/SUVmean) and total kidney accumulation (TKA: SUVmean x renal parenchyma volume) were calculated. All data were correlated with the reference standard tubular extraction rate (TER-MAG) from [^99mTc]Tc-MAG3 scintigraphy and glomerular filtration rate (GFR_{CDK - EPI}).

Results

SUVmean of the parenchymal tracer retention showed a negative correlation with TER_MAG (r: -0.519, p < 0.001) and GFR_{CDK - EPI} (r: -0.555, p < 0.001) at 32 min p.i. The herein-introduced ACI revealed a significant correlation (p < 0.05) with the total tubular function (r: 0.482), glomerular renal function (r: 0.461), split renal function (r: 0.916), and absolute single-sided renal function (r: 0.549). The mean difference between the split renal function determined by renal scintigraphy and ACI was 1.8 ± 4.2 % points.

Conclusion

This pilot study indicates that static [⁶⁸Ga]Ga-ha DOTATATE PET-scans at 32 min p.i. may be used to estimate both split renal function and absolute renal function using the herein proposed "Accumulation Index" (ACI).

The prognostic role of whole-body volumetric 68 GA-DOTATATE PET/computed tomography parameters in patients with gastroenteropancreatic neuroendocrine tumor treated with 177 LU-DOTATATE

OBJECTIVE

The aim of this study is to evaluate the prognostic role of Response Evaluation Criteria in Solid Tumors (RECIST) 1.1 and quantitative 68 Ga-DOTATATE PET/computed tomography parameters such as maximum standardized uptake value (SUVmax), mean SUV (SUVmean), DOTATATE tumor volume (DTV), total lesion DOTATATE (TLD) in patients with gastroenteropancreatic neuroendocrine tumors (GEP-NETs) treated with 177 Lu-DOTATATE.

MATERIAL AND METHOD

Our retrospective study included 21 patients with GEP-NETs treated with 177 Lu-DOTATATE between January 2017 and January 2022. SUVmax, SUVmean, SUVmax/spleenSUVmax (SUVmax/Sx), DTV, TLD, SUVmean/spleenSUVmean (SUVmean/Sm), TLD/Sm values were calculated and recorded for all patients before and after 177 Lu-DOTATATE treatment.

RESULTS

A total of 319 metastases were detected in the patients included in the study, and a total of 68 target lesions were selected. In univariant Cox regression analysis, TLD/Sm percent change (∆TLD/Sm) was found to be statistically significant on overall survival (OS) ( P  = 0.044). The 3-year survival in nonresponders was 50% ( P  = 0.034) based on ∆SUVmax/Sx values, 50% ( P  = 0.002) based on RECIST values, 50% based on ∆TDTV + new lesion values ( P  = 0.033), and according to ∆TTLD + new lesion values, it was 66% ( P  = 0.030).

CONCLUSION

In our study, we showed that SUVmax/Sx, RECIST, ∆TDTV + new lesion, and ∆TTLD + new lesion parameters can predict OS in the evaluation of response to treatment.

Heterogeneity of absorbed dose distribution in kidney tissues and dose–response modelling of nephrotoxicity in radiopharmaceutical therapy with beta-particle emitters: A review

Absorbed dose heterogeneity in kidney tissues is an important issue in radiopharmaceutical therapy. The effect of absorbed dose heterogeneity in nephrotoxicity is, however, not fully understood yet, which hampers the implementation of treatment optimization by obscuring the interpretation of clinical response data and the selection of optimal treatment options. Although some dosimetry methods have been developed for kidney dosimetry to the level of microscopic renal substructures, the clinical assessment of the microscopic distribution of radiopharmaceuticals in kidney tissues currently remains a challenge. This restricts the anatomical resolution of clinical dosimetry, which hinders a thorough clinical investigation of the impact of absorbed dose heterogeneity. The potential of absorbed dose-response modelling to support individual treatment optimization in radiopharmaceutical therapy is recognized and gaining attraction. However, biophysical modelling is currently underexplored for the kidney, where particular modelling challenges arise from the convolution of a complex functional organization of renal tissues with the function-mediated dose distribution of radiopharmaceuticals. This article reviews and discusses the heterogeneity of absorbed dose distribution in kidney tissues and the absorbed dose-response modelling of nephrotoxicity in radiopharmaceutical therapy. The review focuses mainly on the peptide receptor radionuclide therapy with beta-particle emitting somatostatin analogues, for which the scientific literature reflects over two decades of clinical experience. Additionally, detailed research perspectives are proposed to address various identified challenges to progress in this field.

225Ac-Labeled Somatostatin Analogs in the Management of Neuroendocrine Tumors: From Radiochemistry to Clinic

The widespread use of peptide receptor radionuclide therapy (PRRT) represents a major therapeutic breakthrough in nuclear medicine, particularly since the introduction of ¹⁷⁷Lu-radiolabeled somatostatin analogs. These radiopharmaceuticals have especially improved progression-free survival and quality of life in patients with inoperable metastatic gastroenteropancreatic neuroendocrine tumors expressing somatostatin receptors. In the case of aggressive or resistant disease, the use of somatostatin derivatives radiolabeled with an alpha-emitter could provide a promising alternative. Among the currently available alpha-emitting radioelements, actinium-225 has emerged as the most suitable candidate, especially regarding its physical and radiochemical properties. Nevertheless, preclinical and clinical studies on these radiopharmaceuticals are still few and heterogeneous, despite the growing momentum for their future use on a larger scale. In this context, this report provides a comprehensive and extensive overview of the development of ²²⁵Ac-labeled somatostatin analogs; particular emphasis is placed on the challenges associated with the production of ²²⁵Ac, its physical and radiochemical properties, as well as the place of ²²⁵Ac-DOTATOC and ²²⁵Ac-DOTATATE in the management of patients with advanced metastatic neuroendocrine tumors.

Peptide Receptor Radionuclide Therapy in Merkel Cell Carcinoma: A Comprehensive Review

Merkel cell carcinoma is a rare, aggressive skin malignancy, also known as neuroendocrine carcinoma of the skin, with high rates of recurrence and distant metastasis. In refractory metastatic Merkel cell carcinoma (mMCC), besides immunotherapy, chemotherapy, and radiation, peptide receptor radionuclide therapy (PRRT) may be a viable option since this type of tumor can express somatostatin receptors. Methods: We performed a comprehensive review of the literature to evaluate the efficacy of PRRT in mMCC patients. Results: Thirty-seven patients with mMCC received PRRT (1-5 cycles) with ¹⁷⁷Lu- or ⁹⁰Y-labeled somatostatin analogs (cumulative activity, 1.5-30 GBq). Radiographic response was available for 19 of 28 patients who received PRRT alone. Six (31.6%) of 19 patients showed objective responses, from partial to complete, and no severe adverse events were reported. Conclusion: Our analysis supports the use of PRRT in mMCC with sufficient somatostatin receptor uptake, although the quality of the available evidence is low. Prospective clinical trials are already in development and have started accruing in some parts of the world.

Response to Peptide Receptor Radionuclide Therapy in Pheocromocytomas and Paragangliomas: A Systematic Review and Meta-Analysis

INTRODUCTION

Peptide receptor radionuclide therapy (PRRT) with 177Lu-DOTATATE and 90Y-DOTATOC showed efficacy in the metastatic setting of pheocromocytomas (PCCs) and paragangliomas (PGLs) where no standard therapies have been established.

BACKGROUND

A search of peer-reviewed and English articles reporting on 177Lu-DOTATATE and 90Y-DOTATOC efficacy was performed through Medline and Scopus. A subsequent meta-analysis was performed to evaluate the pooled effect size on disease control rate (DCR) with PRRT. Secondary endpoints were description of patients' genetic characteristics, hematologic toxicity, and time-to-outcome. The pooled effect was estimated with both a mixed-effects model and a random-effects model.

RESULTS

Twelve studies met the criteria for this meta-analysis: ten with 177Lu- and two with 90Y-PRRTs (213 patients). The largest one included 46 patients. Median ages ranged from 32.5 to 60.4 years. When reported, mutations of SDHB were the most frequent genetic alterations. The pooled DCRs were 0.83 (95% CI: 0.75-0.88) and 0.76 (95% CI: 0.56-0.89) for 177Lu- and 90Y-PRRT, respectively. The pooled DCR for PRRT was 0.81 (95% CI: 0.74-0.87).

CONCLUSIONS

We report an updated and solid estimate of DCR achieved with 177Lu- and 90Y-PRRT in PCCs and PGLs, showing that these therapies can be considered in the multidisciplinary treatment of PCCs and PGLs as alternatives to I-131 MIBG and chemotherapy.

Phase 1 Study of No-Carrier Added 177Lu-DOTATATE (SNU-KB-01) in Patients with Somatostatin Receptor-Positive Neuroendocrine Tumors: The First Clinical Trial of Peptide Receptor Radionuclide Therapy in Korea

PURPOSE

To provide a wider choice of treatment opportunities for patients with neuroendocrine tumor (NET) in Korea, we have conducted a phase 1, open-label, single-arm, dose-escalation study of SNU-KB-01, a no-carrier added (NCA) 177Lu-labeled DOTATATE.

MATERIALS AND METHODS

Seven patients with inoperable, progressive, metastatic, or locally advanced, somatostatin receptor-positive NET with Ki67 index ≤ 20% were enrolled according to the rolling six design. The study consisted of two cohorts to receive 4 cycles of SNU-KB-01 every 8 weeks for the first dose of 5.55 GBq (n=3) and 7.40 GBq (n=4). We assessed the incidence of dose-limiting toxicity (DLT) and adverse event, absorbed dose of kidneys and bone marrow, and objective tumor response.

RESULTS

Seven patients completed 4 cycles (21.3-30.1 GBq total dose) of SNU-KB-01. The mean absorbed doses to kidneys and bone marrow were 0.500 mGy/MBq and 0.053 mGy/MBq, respectively, and the total body effective dose was 0.115 mSv/MBq. No DLT was observed and the maximum tolerated dose was 7.40 GBq/cycle. Grade 3 thrombocytopenia occurred in one patient, but no other grade 3 or 4 major hematologic or renal toxicity was observed. The best objective response to SNU-KB-01 was partial response. Overall response rate was 42.9% and disease control rate was 85.7%.

CONCLUSION

Treatment with 4 cycles of SNU-KB-01 was well tolerated and resulted in control of disease in most of the patients. Our results indicate SNU-KB-01, an NCA 177Lu-labeled DOTATATE, as a potentially safe and efficacious treatment option for NET patients in Korea.

Rectal neuroendocrine neoplasms: what the radiologists should know

Neuroendocrine neoplasms of the rectum (R-NENs) are rare; however, their incidence has increased almost threefold in the last few decades. Imaging of R-NENs includes two primary categories: anatomic/morphologic imaging comprised of endoscopic ultrasound (EUS), computed tomography (CT), magnetic resonance imaging (MRI), and functional/molecular imaging comprising of planar scintigraphy, single-photon emission computed tomography (SPECT), and positron emission tomography (PET). The management depends on stage, dimension, atypical features, histological grade, and lymphovascular invasion (LVI). Low-risk local R-NENs can be resected endoscopically, and high-risk or locally advanced neoplasms can be treated with radical surgery and lymphadenectomy and/or chemoradiation. The review article focuses on imaging illustrations and discusses applications of different imaging modalities in diagnosing and managing R-NENs.

Targeted Therapies in Pheochromocytoma and Paraganglioma

Molecular targeted therapy plays an increasingly important role in the treatment of metastatic pheochromocytomas and paragangliomas (PPGLs), which are rare tumors but remain difficult to treat. This mini-review provides an overview of established molecular targeted therapies in present use, and perspectives on those currently under development and evaluation in clinical trials. Recently published research articles, guidelines, and expert views on molecular targeted therapies in PPGLs are systematically reviewed and summarized. Some tyrosine kinase inhibitors (sunitinib, cabozantinib) are already in clinical use with some promising results, but without formal approval for the treatment of PPGLs. Sunitinib is the only therapeutic option which has been investigated in a randomized placebo-controlled clinical trial. It is clinically used as a first-, second-, or third-line therapeutic option for the treatment of progressive metastatic PPGLs. Some other promising molecular targeted therapies (hypoxia-inducible factor 2 alpha [HIF2α] inhibitors, tumor vaccination together with checkpoint inhibitors, antiangiogenic therapies, kinase signaling inhibitors) are under evaluation in clinical trials. The HIF2α inhibitor belzutifan may prove to be particularly interesting for cluster 1B-/VHL/EPAS1-related PPGLs, whereas antiangiogenic therapies seem to be primarily effective in cluster 1A-/SDHx-related PPGLs. Some combination therapies currently being evaluated in clinical trials, such as temozolomide/olaparib, temozolomide/talazoparib, or cabozantinib/atezolizumab, will provide data for novel therapy for metastatic PPGLs. It is likely that advances in such molecular targeted therapies will play an essential role in the future treatment of these tumors, with more personalized therapy options paving the way towards improved therapeutic outcomes.

Treatment strategies for neuroendocrine liver metastases: a systematic review

BACKGROUND

Gastroenteropancreatic neuroendocrine tumors are often diagnosed when metastatic. The liver is the main site of metastases. Unfortunately, optimal management of neuroendocrine liver metastases remains a topic of debate. The aim of this study was to make a systematic review of the current literature about the results of the different treatments of neuroendocrine liver metastases.

METHODS

A systematic review was conducted for English language publications from 1995 to 2021. Outcomes were analyzed according to survival, disease-free survival, and in the case of systemic therapies, progression-free survival.

RESULTS

5509 patients were analyzed in the review. 67% of patients underwent surgery achieving 5 years overall survival despite only 30% percent without a recurrence. 60% of patients that had received a transplant reached 5 years survival with a low disease-free survival rate (20%). Five-year survival rate was 36.2% for patients undergoing loco-regional therapies.

CONCLUSION

Surgical resection is the best treatment when metastases are resectable, with the highest rate of survival, although liver transplantation shows good results for patients not eligible for surgery. Loco-regional therapies may be useful when surgical resection is contraindicated, or selectively used as a bridge to surgery or transplantation. Systemic therapies are indicated in patients for whom curative treatment cannot be obtained.

Imaging-guided targeted radionuclide tumor therapy: From concept to clinical translation

Since the first introduction of sodium iodide I-131 for use with thyroid patients almost 80 years ago, more than 50 radiopharmaceuticals have reached the markets for a wide range of diseases, especially cancers. The nuclear medicine paradigm also shifts from solely molecular imaging or radionuclide therapy to imaging-guided radionuclide therapy, which is deemed a vital component of precision cancer therapy and an emerging medical modality for personalized medicine. The imaging-guided radionuclide therapy highlights the systematic integration of targeted nuclear diagnostics and radionuclide therapeutics. Regarding this, nuclear imaging serves to "visualize" the lesions and guide the therapeutic strategy, followed by administration of a precise patient specific dose of radiotherapeutics for treatment according to the absorbed dose to different organs and tumors calculated by dosimetry tools, and finally repeated imaging to predict the prognosis. This strategy leads to significantly enhanced therapeutic efficacy, improved patient outcomes, and manageable adverse events. In this review, we provide an overview of imaging-guided targeted radionuclide therapy for different tumors such as advanced prostate cancer and neuroendocrine tumors, with a focus on development of new radioligands and their preclinical and clinical results, and further discuss about challenges and future perspectives.

Glucose Metabolism Modification Induced by Radioligand Therapy with [177Lu]Lu/[90Y]Y-DOTATOC in Advanced Neuroendocrine Neoplasms: A Prospective Pilot Study within FENET-2016 Trial

[18F]F-FDG (FDG) PET is emerging as a relevant diagnostic and prognostic tool in neuroendocrine neoplasms (NENs), as a simultaneous decrease in [68Ga]Ga-DOTA peptides and increase in FDG uptake (the “flip-flop” phenomenon) occurs during the natural history of these tumors. The aim of this study was to evaluate the variations on FDG PET in NEN patients treated with two different schemes of radioligand therapy (RLT) and to correlate them with clinical−pathologic variables. A prospective evaluation of 108 lesions in 56 patients (33 males and 23 females; median age, 64.5 years) affected by NENs of various primary origins (28 pancreatic, 13 gastrointestinal, 9 bronchial, 6 unknown primary (CUP-NENs) and 1 pheochromocytoma) and grades (median Ki-67 = 9%) was performed. The patients were treated with RLT within the phase II clinical trial FENET-2016 (CTID: NCT04790708). RLT was offered for 32 patients with the MONO scheme (five cycles of [177Lu]Lu-DOTATOC) and for 24 with the DUO scheme (three cycles of [177Lu]Lu-DOTATOC alternated with two cycles of [90Y]Y-DOTATOC). Variations in terms of the ΔSUVmax of a maximum of three target lesions per patient (58 for MONO and 50 for DUO RLT) were assessed between baseline and 3 months post-RLT FDG PET. In patients with negative baseline FDG PET, the three most relevant lesions on [68Ga]Ga-DOTA-peptide PET were assessed and matched on post-RLT FDG PET, to check for any possible changes in FDG avidity. Thirty-five patients (62.5%) had at least one pathological FDG uptake at the baseline scans, but the number was reduced to 29 (52%) after RLT. In the patients treated with DUO-scheme RLT, 20 out of 50 lesions were FDG positive before therapy, whereas only 14 were confirmed after RLT (p = 0.03). Moreover, none of the 30 FDG-negative lesions showed an increased FDG uptake after RLT. The lesions of patients with pancreatic and CUP-NENs treated with the DUO scheme demonstrated a significant reduction in ΔSUVmax in comparison to those treated with MONO RLT (p = 0.03 and p = 0.04, respectively). Moreover, we found a mild positive correlation between the grading and ΔSUVmax in patients treated with the MONO scheme (r = 0.39, p < 0.02), while no evidence was detected for patients treated with the DUO scheme. Our results suggest that RLT, mostly with the DUO scheme, could be effective in changing NEN lesions’ glycometabolism, in particular, in patients affected by pancreatic and CUP-NENs, regardless of their Ki-67 index. Probably, associating [90Y]Y-labelled peptides, which have high energy emission and a crossfire effect, and [177Lu]Lu ones, characterized by a longer half-life and a safer profile for organs at risk, might represent a valid option in FDG-positive NENs addressed to RLT. Further studies are needed to validate our preliminary findings. In our opinion, FDG PET/CT should represent a potent tool for fully assessing a patient’s disease characteristics, both before and after RLT.

Association between fibrosis markers and kidney function following peptide receptor radionuclide therapy in patients with neuroendocrine tumours

Peptide receptor radionuclide therapy (PRRT) is a treatment for neuroendocrine tumours (NET). Renal impairment is a known side effect due to kidney fibrosis. We investigated the association between novel specific fibrosis markers and kidney function following PRRT. We included 38 patients who had all finished PRRT. In serum and urine, we analysed levels of three different fibrosis markers, PRO-C6 (type VI collagen formation), PRO-C3 (type III collagen formation) and C3M (type III collagen degradation). We determined kidney function by the ⁵¹Cr-EDTA plasma clearance. We used Wilcoxon rank sum test and Spearman's rank correlation to evaluate the association between the fibrosis markers and kidney function. We included 38 NET patients, 25 small-intestinal NET, 6 pancreatic NET, 2 pulmonary NET and 5 other types of NET. Median age was 69 years (IQR: 61-73). Median time from last PRRT to inclusion was 8 months (IQR: 3-20). We found significantly increased levels of serum PRO-C6 (p = .007) and urinary PRO-C6 (p = .033) and significantly decreased levels of urinary C3M (p = .035) in patients with impaired kidney function. Further, we observed a negative association between serum PRO-C6 and kidney function (rho = -0.33, p = .04) and a positive association between urinary C3M and kidney function (rho = 0.37, p = .02). We showed an association between the three fibrosis markers, serum PRO-C6, urinary PRO-C6 and urinary C3M and kidney function. These markers may help to improve the understanding of potential pathological tissue turnover and potentially improve monitoring of kidney function after PRRT in NET patients.

Radionuclides for Targeted Therapy: Physical Properties

A search in PubMed revealed that 72 radionuclides have been considered for molecular or functional targeted radionuclide therapy. As radionuclide therapies increase in number and variations, it is important to understand the role of the radionuclide and the various characteristics that can render it either useful or useless. This review focuses on the physical characteristics of radionuclides that are relevant for radionuclide therapy, such as linear energy transfer, relative biological effectiveness, range, half-life, imaging properties, and radiation protection considerations. All these properties vary considerably between radionuclides and can be optimised for specific targets. Properties that are advantageous for some applications can sometimes be drawbacks for others; for instance, radionuclides that enable easy imaging can introduce more radiation protection concerns than others. Similarly, a long radiation range is beneficial in targets with heterogeneous uptake, but it also increases the radiation dose to tissues surrounding the target, and, hence, a shorter range is likely more beneficial with homogeneous uptake. While one cannot select a collection of characteristics as each radionuclide comes with an unchangeable set, all the 72 radionuclides investigated for therapy—and many more that have not yet been investigated—provide numerous sets to choose between.

Systemic Therapy of Advanced Well-differentiated Small Bowel Neuroendocrine Tumors Progressive on Somatostatin Analogues

OPINION STATEMENT

Neuroendocrine neoplasms (NENs) are a heterogeneous group of tumors whose management requires a nuanced and multi-disciplinary approach in order to control symptoms, halt tumor growth, and improve survival outcomes. Of late, the treatment landscape of NENs has advanced considerably as a result of several pivotal clinical trials, which have established somatostatin analogues as first-line therapy for advanced, metastatic, well-differentiated neuroendocrine tumors (NETs). However, an evolving classification system as well as an increased understanding of distinct clinical, molecular, and biologic features contribute to complexity in management. In particular, there remains limited randomized prospective data in the somatostatin analogue (SSA)-refractory setting for patients with primary tumors that originate in the small bowel. For well-differentiated small bowel neuroendocrine tumors (SBNETs), treatment beyond SSAs includes radionuclide therapy, targeted agents, liver-directed therapy, and to a lesser extent, cytotoxic chemotherapy. In the current era, selection of these agents is largely based on expert opinion in the context of patient and tumor characteristics without definitive data on the preferred order of agents to administer. In this review, we aim to describe the treatment landscape of metastatic SBNETs beyond SSAs and provide an overview of novel treatments which are currently under clinical evaluation.

Individualization of Radionuclide Therapies: Challenges and Prospects

Simple Summary

Currently, patient-specific treatment plans and dosimetry calculations are not routinely performed for radionuclide therapies. In external beam radiotherapy, it is quite the opposite. As a result, a small fraction of patients receives optimal radioactivity. This conservative approach provides “radiation safety” to healthy tissues but delivers a lower than indicated absorbed dose to the tumors, resulting in a lower response rate and a higher disease relapse rate. Evidence shows that better and more predictable outcomes can be achieved with patient-individualized dose assessment. Therefore, the incorporation of individual planning into radionuclide therapies is a high priority for nuclear medicine physicians and medical physicists alike. Internal dosimetry is used in tumor therapy to optimize the absorbed dose to the target tissue. The main reasons for the difficulties in incorporating patients’ internal dosimetry into routine clinical practice are discussed. The article presents the prospects for the routine implementation of personalized radionuclide therapies.

Abstract

The article presents the problems of clinical implementation of personalized radioisotope therapy. The use of radioactive drugs in the treatment of malignant and benign diseases is rapidly expanding. Currently, in the majority of nuclear medicine departments worldwide, patients receive standard activities of therapeutic radiopharmaceuticals. Intensively conducted clinical trials constantly provide more evidence of a close relationship between the dose of radiopharmaceutical absorbed in pathological tissues and the therapeutic effect of radioisotope therapy. Due to the lack of individual internal dosimetry (based on the quantitative analysis of a series of diagnostic images) before or during the treatment, only a small fraction of patients receives optimal radioactivity. The vast majority of patients receive too-low doses of ionizing radiation to the target tissues. This conservative approach provides “radiation safety” to healthy tissues, but also delivers lower radiopharmaceutical activity to the neoplastic tissue, resulting in a low level of response and a higher relapse rate. The article presents information on the currently used radionuclides in individual radioisotope therapies and on radionuclides newly introduced to the therapeutic market. It discusses the causes of difficulties with the implementation of individualized radioisotope therapies as well as possible changes in the current clinical situation.

Factors Contributing to Tumor Shrinkage after Peptide Receptor Radionuclide Therapy in Patients with Unresectable Neuroendocrine Tumors

Peptide receptor activation therapy (PRRT) is a promising treatment option for metastatic neuroendocrine tumors (NETs). However, predicting tumor shrinkage before treatment is challenging. We analyzed the shrinkage rate of each metastatic tumor lesion to identify predictive factors related to shrinkage. Patients with metastatic NET who underwent PRRT were included in this retrospective study. For each patient, between one to five metastatic lesions were selected in descending order of size, and the change in the maximum tumor diameter after treatment was defined as the shrinkage rate per lesion (L-SR). We analyzed the relationship between pretreatment clinicopathological factors and L-SR. The median L-SR of all 75 lesions in 20 patients was 20% (95% CI: 4.8−26.1%). While previous treatment with cytotoxic agents (34.4%, p < 0.05) and primary tumor of the pancreas (27.8%, p < 0.05) were significantly favorable factors, a primary tumor of the rectum was significantly more resistant to shrinkage (−20.5%, p < 0.001). Therefore, lesion-based analysis of PRRT for NETs showed that pancreatic NET and previous treatment with cytotoxic agents were favorable factors for tumor shrinkage; however, rectal NET was a factor associated with resistance to shrinkage.

Real-world efficacy of lutetium peptide receptor radionuclide therapy in patients with neuroendocrine tumours

Lutetium peptide receptor radio nuclide therapy (Lu-PRRT) is an effective treatment for progressive, metastatic, somatostatin-receptor-positive, well-differentiated neuroendocrine tumours (WD-NETs). Here, we report a single centre experience of real-world efficacy, long-term side effects, and challenges of this treatment. This was a retrospective analysis. All patients linked with our centre who had Lu-PRRT were included. Clinicopathological data were analysed using descriptive statistics, Kaplan-Meier, and Cox regression. A total of 45 patients had Lu-PRRT, of those 30 (67%) were males, and 13 (29%) were more than 65 years old. The primary site was small intestine in 30 (67%) patients, pancreas in seven (16%) patients, and lung in three (7%) patients. The tumor was grade 1 in 15 (35%) patients, grade 2 in 22 (48%) patients, and grade 3 in six (13%) patients. A total of 41 (91%) patients had liver metastasis, and 20 (44%) patients had carcinoid syndrome. Lu-PRRT was the second-line therapy in all patients. Krenning's score was 4 in 36 (80%) patients and 3 in nine (20%) patients. The median waiting time to start Lu-PRRT therapy was 87 days. The median follow-up was 41 months. A total of 23 (51%) patients had a partial response, 18 (40%) patients had stable disease, and four (9%) patients had progression. None of the patients had a complete response. The median progression-free survival (PFS) was 38 months (95% CI: 25.8-50.1). The median overall survival (OS) was not reached. Nine patients died during follow-up (death from any cause). Prior treatment with targeted therapies or high dose somatostatin analogues were negative predictors of Lu-PRRT outcome (p-values of < .001 and < .045, respectively). There were two serious haematological toxicities, one patient developed acute myeloid leukaemia (AML), and the other developed chronic myeloid leukaemia (CML). Lu-PRRT is an effective second-line treatment for metastatic WD-NETs. The effect of targeted therapies on Lu-PRRT outcome was significant and needs to be clarified in further studies.

Severe Thrombocytopenia in Patients With Advanced Neuroendocrine Tumor Treated With Peptide Receptor Radioligand Therapy

BACKGROUND

Peptide receptor radioligand therapy (PRRT) was Food and Drug Administration approved in 2018 for the treatment of unresectable somatostatin receptor-positive gastroenteropancreatic neuroendocrine tumors (NETs) and provides an important option for patients with advanced disease. A known adverse effect of this treatment is hematologic toxicity, although usually transient. We present 3 patients with metastatic gastroenteropancreatic NETs treated with PRRT who were evaluated for severe persistent thrombocytopenia.

METHODS

Three patients who commenced therapy with PRRT were known to proceed to a bone marrow (BM) biopsy for persistent severe thrombocytopenia and were included in this study. These patients were identified retrospectively and evaluated for their tumor properties, including immunohistochemical markers, treatment modalities, and clinical outcomes.

RESULTS

All 3 patients had metastatic NETs that progressed on prior lines of therapy and were treated with 1 to 4 doses of 177Lu-DOTATATE 7.4 GBq (200 mCi) before developing grade 3 (25,000 to 50,000/μL) refractory thrombocytopenia. All patients had concurrent bone metastases, and 2 of the 3 had baseline grade 1 thrombocytopenia. In all 3 cases, BM biopsy documented widespread tumor infiltration.

CONCLUSIONS

Severe refractory thrombocytopenia after PRRT is rare and may result from numerous known causes, including radiation-induced myelotoxicity, myelodysplastic syndrome, and tumor BM infiltration. We present 3 cases of thrombocytopenia related to persistent or progressive BM metastasis. Although known bone metastasis is not a contraindication to PRRT, thrombocytopenia may be a manifestation of tumor progression and should be considered when making decisions about continuation of therapy.

Net theranostics

Theranostics is a term coined by combining the words “therapeutics” and “diagnostics,” referring to single chemical entities developed to deliver therapy and diagnosis simultaneously. Neuroendocrine tumors are rare cancers that occur in various organs of the body, and they express neuroendocrine factors such as chromogranin A and somatostatin receptor. Somatostatin analogs bind to somatostatin receptor, and when combined with diagnostic radionuclides, such as gamma‐emitters, are utilized for diagnosis of neuroendocrine tumor. Somatostatin receptor scintigraphy when combined with therapeutic radionuclides, such as beta‐emitters, are effective in treating neuroendocrine tumor as peptide receptor radionuclide therapy. Somatostatin receptor scintigraphy and peptide receptor radionuclide therapy are some of the most frequently used and successful theranostics for neuroendocrine tumor. In Japan, radiopharmaceuticals are regulated under a complex law system, creating a significant drug lag, which is a major public concern. It took nearly 10 years to obtain the approval for somatostatin receptor scintigraphy and peptide receptor radionuclide therapy use by the Japanese government. In 2021, ¹¹¹Lu‐DOTATATE (Lutathera), a drug for peptide receptor radionuclide therapy, was covered by insurance in Japan. In this review, we summarize the history of the development of neuroendocrine tumor theranostics and theranostics in general, as therapeutic treatment for cancer in the future. Furthermore, we briefly address the Japanese point of view regarding the development of new radiopharmaceuticals.