Expression of somatostatin receptor subtypes in human brain tumors

Targeted Radionuclide Therapy in Glioblastoma

Despite the development of various novel therapies, glioblastoma (GBM) remains a devastating disease, with a median survival of less than 15 months. Recently, targeted radionuclide therapy has shown significant progress in treating solid tumors, with the approval of Lutathera for neuroendocrine tumors and Pluvicto for prostate cancer by the US Food and Drug Administration (FDA) and the European Medicines Agency (EMA). This achievement has shed light on the potential of targeted radionuclide therapy for other solid tumors, including GBM. This review presents the current status of targeted radionuclide therapy in GBM, highlighting the commonly used therapeutic radionuclides emitting alpha, beta particles, and Auger electrons that could induce potent molecular and cellular damage to treat GBM. We then explore a range of targeting vectors, including small molecules, peptides, and antibodies, which selectively target antigen-expressing tumor cells with minimal or no binding to healthy tissues. Considering that radiopharmaceuticals for GBM are often administered locoregionally to bypass the blood-brain barrier (BBB), we review prominent delivery methods such as convection-enhanced delivery, local implantation, and stereotactic injections. Finally, we address the challenges of this therapeutic approach for GBM and propose potential solutions.

PET imaging of gliomas: Status quo and quo vadis?

PET imaging, particularly using amino acid tracers, has become a valuable adjunct to anatomical MRI in the clinical management of patients with glioma. Collaborative international efforts have led to the development of clinical and technical guidelines for PET imaging in gliomas. The increasing readiness of statutory health insurance agencies, especially in European countries, to reimburse amino acid PET underscores its growing importance in clinical practice. Integrating artificial intelligence and radiomics in PET imaging of patients with glioma may significantly improve tumor detection, segmentation, and response assessment. Efforts are ongoing to facilitate the clinical translation of these techniques. Considerable progress in computer technology developments (eg quantum computers) may be helpful to accelerate these efforts. Next-generation PET scanners, such as long-axial field-of-view PET/CT scanners, have improved image quality and body coverage and therefore expanded the spectrum of indications for PET imaging in Neuro-Oncology (eg PET imaging of the whole spine). Encouraging results of clinical trials in patients with glioma have prompted the development of PET tracers directing therapeutically relevant targets (eg the mutant isocitrate dehydrogenase) for novel anticancer agents in gliomas to improve response assessment. In addition, the success of theranostics for the treatment of extracranial neoplasms such as neuroendocrine tumors and prostate cancer has currently prompted efforts to translate this approach to patients with glioma. These advancements highlight the evolving role of PET imaging in Neuro-Oncology, offering insights into tumor biology and treatment response, thereby informing personalized patient care. Nevertheless, these innovations warrant further validation in the near future.

Joint EANM/EANO/RANO/SNMMI practice guideline/procedure standards for diagnostics and therapy (theranostics) of meningiomas using radiolabeled somatostatin receptor ligands: version 1.0

PURPOSE

To provide practice guideline/procedure standards for diagnostics and therapy (theranostics) of meningiomas using radiolabeled somatostatin receptor (SSTR) ligands.

METHODS

This joint practice guideline/procedure standard was collaboratively developed by the European Association of Nuclear Medicine (EANM), the Society of Nuclear Medicine and Molecular Imaging (SNMMI), the European Association of Neurooncology (EANO), and the PET task force of the Response Assessment in Neurooncology Working Group (PET/RANO).

RESULTS

Positron emission tomography (PET) using somatostatin receptor (SSTR) ligands can detect meningioma tissue with high sensitivity and specificity and may provide clinically relevant information beyond that obtained from structural magnetic resonance imaging (MRI) or computed tomography (CT) imaging alone. SSTR-directed PET imaging can be particularly useful for differential diagnosis, delineation of meningioma extent, detection of osseous involvement, and the differentiation between posttherapeutic scar tissue and tumour recurrence. Moreover, SSTR-peptide receptor radionuclide therapy (PRRT) is an emerging investigational treatment approach for meningioma.

CONCLUSION

These practice guidelines will define procedure standards for the application of PET imaging in patients with meningiomas and related SSTR-targeted PRRTs in routine practice and clinical trials and will help to harmonize data acquisition and interpretation across centers, facilitate comparability of studies, and to collect larger databases. The current document provides additional information to the evidence-based recommendations from the PET/RANO Working Group regarding the utilization of PET imaging in meningiomas Galldiks (Neuro Oncol. 2017;19(12):1576-87). The information provided should be considered in the context of local conditions and regulations.

Clinical value of semi-quantitative parameters in 68Ga-DOTANOC PET/CT in treatment and diagnostics of cranial meningioma in a single-center retrospective analysis

BACKGROUND

The value of somatostatin-analogon PET tracers in theranostics in cranial meningioma has been demonstrated in several studies however, the value of semi-quantitative parameters for therapy and patient outcome is still unclear.

METHODS

A retrospective study was performed comparing measured semi-quantitative 68Ga-DOTANOC PET/CT parameters (maximum standardized uptake value = SUVmax, mean standardized uptake value = SUVmean, and metabolic tumor volume = MTV) and calculated ratios (SUVmax tumor/to pituitary gland, SUVmax tumor to superior sinus sagittalis), versus WHO grades and overall outcome. Patients with histological confirmed meningioma or high probability for meningioma in previous cranial MRI were eligible.

RESULTS

Thirty-two patients from January 2018 to February 2023 were retrospectively included. WHO grade I meningioma was confirmed in 17 patients, WHO grade II in five patients, WHO grade III in two patients, while in eight patients diagnosis was solely based on MRI and 68Ga-DOTANOC PET/CT findings. In 12 cases stable disease was present, in 15 cases radiation therapy was chosen, in three cases neurosurgery was preferred while in two cases palliative care was chosen. Median SUVmax values increased with WHO grade (15.84, 17.22, and 28.4, p = 0.134, Kruskal-Wallis-test) and no statistically significant difference was present for MTV, SUVmax, and calculated ratios, although the ratio for SUVmax tumor to superior sinus sagittalis had the lowest value of p = 0.067.

CONCLUSION

Increased SUVmax values in the tumor in 68Ga-DOTANOC PET/CT are associated with higher WHO grade, although further studies including larger patient collectives are needed to solidify this hypothesis.

Clinical value of semi-quantitative parameters in 68Ga-DOTANOC PET/CT in treatment and diagnostics of cranial meningioma in a single-center retrospective analysis

BACKGROUND

The value of somatostatin-analogon PET tracers in theranostics in cranial meningioma has been demonstrated in several studies; however, the value of semi-quantitative parameters for therapy and patient outcome is still unclear.

METHODS

A retrospective study was performed comparing measured semi-quantitative 68Ga-DOTANOC PET/CT parameters (maximum standardized uptake value = SUVmax, mean standardized uptake value = SUVmean, and metabolic tumor volume = MTV) and calculated ratios (SUVmax tumor to pituitary gland and SUVmax tumor to superior sinus sagittalis), versus the WHO grades and overall outcome. Patients with histological confirmed meningioma or high probability for meningioma in the previous cranial MRI were eligible.

RESULTS

Thirty-two patients from January 2018 to February 2023 were retrospectively included. The WHO grade I meningioma was confirmed in 17 patients, the WHO grade II in five patients, and the WHO grade III in two patients, while in eight patients, diagnosis was solely based on MRI and 68Ga-DOTANOC PET/CT findings. In 12 cases, stable disease was present, in 15 cases, radiation therapy was chosen, in three cases, neurosurgery was preferred, while in two cases, palliative care was chosen. Median SUVmax values increased with the WHO grade (15.84, 17.22, and 28.4, p = 0.134, Kruskal-Wallis test), and no statistically significant difference was present for MTV, SUVmax, and calculated ratios.

CONCLUSION

Increased SUVmax values in the tumor in 68Ga-DOTANOC PET/CT are associated with higher WHO grade, although further studies including larger patient collectives are needed to solidify this hypothesis.

A Prospective Registry Study of 68Ga-DOTATATE PET/CT Incorporation Into Treatment Planning of Intracranial Meningiomas

PURPOSE

The current standard for meningioma treatment planning involves magnetic resonance imaging-based guidance. Somatostatin receptor ligands such as 68Ga-DOTATATE are being explored for meningioma treatment planning due to near-universal expression of somatostatin receptors 1 and 2 in meningioma tissue. We hypothesized that 68Ga-DOTATATE positron emission tomography (PET)-guided treatment management for patients with meningiomas is safe and effective and can identify which patients benefit most from adjuvant radiation therapy.

METHODS AND MATERIALS

A single-institution prospective registry study was created for inclusion of patients with intracranial meningiomas who received a 68Ga-DOTATATE PET/CT to assist with radiation oncologist decision making. Patients who received a PET scan from January 1, 2018, to February 25, 2022, were eligible for inclusion.

RESULTS

Of the 60 patients included, 40%, 47%, and 5% had World Health Organization grades 1, 2, and 3 meningiomas, respectively, and 8% (5 patients) had no grade assigned. According to Radiation Therapy Oncology Group 0539 criteria, 22%, 72%, and 7% were categorized as high, intermediate, and low risk, respectively. After completing their PET scans, 48 patients, 11 patients, and 1 patient proceeded with radiation therapy, observation, and redo craniotomy, respectively. The median follow-up for the entire cohort was 19.5 months. Of the 3 patients (5%) who experienced local failure between 9.2 and 28.5 months after diagnosis, 2 had PET-avid disease in their postoperative cavity and elected for observation before recurrence, and 1 high-risk patient with multifocal disease experienced local failure 2 years after a second radiation course and multiple previous recurrences. Notably, 5 patients did not have any local PET uptake and were observed; none of these patients experienced recurrence. Only 1 grade 3 toxicity was attributed to PET-guided radiation.

CONCLUSIONS

This study examined one of the largest known populations of patients with intracranial meningiomas followed by physicians who used 68Ga-DOTATATE PET-guided therapy. Incorporating 68Ga-DOTATATE PET into future trials may assist with clinician decision making and improve patient outcomes.

Theranostics in Neurooncology: Heading Toward New Horizons

Therapeutic approaches to brain tumors remain a challenge, with considerable limitations regarding delivery of drugs. There has been renewed and increasing interest in translating the popular theranostic approach well known from prostate and neuroendocrine cancer to neurooncology. Although far from perfect, some of these approaches show encouraging preliminary results, such as for meningioma and leptomeningeal spread of certain pediatric brain tumors. In brain metastases and gliomas, clinical results have failed to impress. Perspectives on these theranostic approaches regarding meningiomas, brain metastases, gliomas, and common pediatric brain tumors will be discussed. For each tumor entity, the general context, an overview of the literature, and future perspectives will be provided. Ongoing studies will be discussed in the supplemental materials. As most theranostic agents are unlikely to cross the blood-brain barrier, the delivery of these agents will be dependent on the successful development and clinical implementation of techniques enhancing permeability and retention. Moreover, the international community should strive toward sufficiently large and randomized studies to generate high-level evidence on theranostic approaches with radioligand therapies for central nervous system tumors.

Transforming Neurology and Psychiatry: Organ-specific PET Instrumentation and Clinical Applications

PET technology has immense potential for furthering understanding of the brain and associated disorders, including advancements in high-resolution tomographs and hybrid imaging modalities. Novel radiotracers targeting specific neurotransmitter systems and molecular markers provide opportunities to unveil intricate mechanisms underlying neurologic and psychiatric conditions. As PET imaging techniques and analysis methods continue to be refined, the field is poised to make significant contributions to personalized medicine for more targeted and effective interventions. PET instrumentation has advanced the fields of neurology and psychiatry, providing insights into pathophysiology and development of effective treatments.

Somatostatin and Somatostatin Receptors in Tumour Biology

Somatostatin (SST), a growth hormone inhibitory peptide, is expressed in endocrine and non-endocrine tissues, immune cells and the central nervous system (CNS). Post-release from secretory or immune cells, the first most appreciated role that SST exhibits is the antiproliferative effect in target tissue that served as a potential therapeutic intervention in various tumours of different origins. The SST-mediated in vivo and/or in vitro antiproliferative effect in the tumour is considered direct via activation of five different somatostatin receptor subtypes (SSTR1-5), which are well expressed in most tumours and often more than one receptor in a single cell. Second, the indirect effect is associated with the regulation of growth factors. SSTR subtypes are crucial in tumour diagnosis and prognosis. In this review, with the recent development of new SST analogues and receptor-specific agonists with emerging functional consequences of signaling pathways are promising therapeutic avenues in tumours of different origins that are discussed.

Decoding meningioma heterogeneity and neoplastic cell-macrophage interaction through single-cell transcriptome profiling across pathological grades

BACKGROUND

Analyzing meningioma of distinct pathological types at the single-cell level can provide new and valuable insights into the specific biological mechanisms of each cellular subpopulation, as well as their vital interplay within the tumor microenvironment.

METHODS

We recruited patients diagnosed with four distinct types of meningioma and performed single-cell RNA sequencing on their tumor samples, concurrently analyzing a publicly available dataset for comparison. Next, we separated the cells into discrete clusters and identified their unique identities. Using pseudotime analysis, we demonstrated cellular differentiation and dynamics. To investigate biological function, we employed weighted gene co-expression network analysis, gene regulatory network, and gene set enrichment analysis. Additionally, we conducted cell-cell communication analyses to characterize interactions among different clusters and validated a crucial interaction using multiple immunofluorescence staining.

RESULTS

The single-cell transcriptomic profiles for five meningioma of different pathological types demonstrated that neoplastic cells exhibited high inter-sample heterogeneity and diverse biological functions featured by metabolic regulation. A small cluster of neoplastic cells (N5 cluster, < 3%) was most proliferative, indicated by high expression of MKI67 and TOP2A. They were primarily observed in our atypical and transitional meningioma samples and located at the beginning of the pseudotime differentiation branch for neoplastic cells. Macrophages, the most abundant immune cells present, showed two distinct developmental trajectories, one promoting and the other suppressing meningioma growth, with the MIF-CD74 interaction serving as the primary signaling pathway for MIF signals in the tumor environment. Unexpectedly, despite its small cluster size, the N5 cluster demonstrated a significant contribution in this interaction. By staining pathological sections of more samples, we found that this interaction was widely present in different types of meningiomas.

CONCLUSIONS

Meningioma neoplastic cells' diverse types cause inter-sample heterogeneity and a wide range of functions. Some proliferative neoplastic cell may educate macrophages, which promotes tumorigenesis possibly through the MIF-CD74 interaction. It provides novel clues for future potential therapeutic avenues.

Somatostatin receptor subtype expression and radiomics from DWI-MRI represent SUV of [68Ga]Ga-DOTATOC PET in patients with meningioma

OBJECTIVE

This retrospective study aimed to analyse the correlation between somatostatin receptor subtypes (SSTR 1-5) and maximum standardized uptake value (SUVmax) in meningioma patients using Gallium-68 DOTA-D-Phe1-Tyr3-octreotide Positron Emission Tomography ([68Ga]Ga-DOTATOC PET). Secondly, we developed a radiomic model based on apparent diffusion coefficient (ADC) maps derived from diffusion weighted magnetic resonance images (DWI MRI) to reproduce SUVmax.

METHOD

The study included 51 patients who underwent MRI and [68Ga]Ga-DOTATOC PET before meningioma surgery. SUVmax values were quantified from PET images and tumour areas were segmented on post-contrast T1-weighted MRI and mapped to ADC maps. A total of 1940 radiomic features were extracted from the tumour area on each ADC map. A random forest regression model was trained to predict SUVmax and the model's performance was evaluated using repeated nested cross-validation. The expression of SSTR subtypes was quantified in 18 surgical specimens and compared to SUVmax values.

RESULTS

The random forest regression model successfully predicted SUVmax values with a significant correlation observed in all 100 repeats (p < 0.05). The mean Pearson's r was 0.42 ± 0.07 SD, and the root mean square error (RMSE) was 28.46 ± 0.16. SSTR subtypes 2A, 2B, and 5 showed significant correlations with SUVmax values (p < 0.001, R2 = 0.669; p = 0.001, R2 = 0.393; and p = 0.012, R2 = 0.235, respectively).

CONCLUSION

SSTR subtypes 2A, 2B, and 5 correlated significantly with SUVmax in meningioma patients. The developed radiomic model based on ADC maps effectively reproduces SUVmax using [68Ga]Ga-DOTATOC PET.

Benefits of combined use of 68-Ga Dotatoc and 5-ALA fluorescence for recurrent atypical skull-base meningioma after previous microsurgery and Gamma Knife radiosurgery: a case report

BACKGROUND

Studies of novel microsurgical adjuncts, such as 5-aminolevulinic acid (5-ALA) fluorescence have shown various fluorescence patterns within meningiomas, opening new avenues for complete microsurgical resection. Here, we present a recurrent, radiation-induced meningioma, previously operated on two occasions (initial gross total resection and subtotal 12 years later) and also irradiated by Gamma Knife radiosurgery (GKR, 6 years after the first surgery). We thought to assess the usefulness of ^68-Ga Dotatoc in surgical target planning and of 5-ALA as an adjunct for maximal microsurgical excision.

CASE REPORT

We report on a 43 years-old Caucasian male diagnosed with atypical, radiation induced WHO II meningioma, with left basal temporal bone implantation. Hodgkin lymphoma treated with cranial and mediastinal radiation during infancy marked his personal history. He underwent a first gross total microsurgical resection, followed 6 and 12 years later by Gamma Knife radiosurgery (GKR) and second subtotal microsurgical resection, respectively. Magnetic resonance imaging (MRI) displayed new recurrence 13 years after initial diagnosis. He was clinically asymptomatic but routine Magnetic resonance imaging showed constant progression. There was strong ^68-Ga Dotatoc uptake. We used 5-ALA guided microsurgical resection. Intraoperative views confirmed strong fluorescence, in concordance with both preoperative Magnetic resonance imaging enhancement and ^68-Ga Dotatoc. The tumor was completely removed, with meningeal and bone resection.

CONCLUSION

The authors conclude that fluorescence-guided resection using 5-ALA is useful for recurrent atypical, radiation-induced meningioma even despite previous irradiation and multiple recurrences.

Optic Nerve Sheath Meningiomas: Solving Diagnostic Challenges with 68Ga-DOTATOC PET/CT

⁶⁸Ga-DOTATOC PET could be a noninvasive, highly sensitive, and specific technique for the challenging diagnosis of optic nerve sheath meningioma (ONSM). Our objective was to report the use and results of ⁶⁸Ga-DOTATOC PET in suspected ONSM. Twelve subjects who underwent ⁶⁸Ga-DOTATOC PET for suspected ONSM in our department were retrospectively included. Standardised clinical and radiological data were collected. The PET examination results were classified as positive or negative, and lesion standardised uptake values (SUV_max) were recorded. ⁶⁸Ga-DOTATOC PET confirmed positive uptake in six cases (SUV_max > 5), leading to ONSM diagnoses followed by radiation therapy in patients with vision loss. Six ⁶⁸Ga-DOTATOC PET scans were considered negative (SUV_max < 5); these comprised one case of neurosarcoidosis, one cavernous malformation, and four uncertain diagnoses, leading to further investigation. ⁶⁸Ga-DOTATOC PET was helpful in tumour volume delineation before radiation therapy, leading to a decrease in dose exposure. Noninvasive ⁶⁸Ga-DOTATOC PET should be performed before treating nonhistologically proven meningiomas with radiotherapy or stereotactic radiosurgery, particularly in cases of uncertain diagnosis with MRI, which characterises most ONSM cases. PET SUV_max thresholds to distinguish meningioma from nonspecific uptake in other lesions need to be adapted to ONSM. ⁶⁸Ga-DOTATOC PET improves the intraorbital lesion diagnostic approach and therefore impacts therapeutic management.

Advanced Meningioma Imaging

Noninvasive imaging methods are used to accurately diagnose meningiomas and track their growth and location. These techniques, including computed tomography, MRI, and nuclear medicine, are also being used to gather more information about the biology of the tumors and potentially predict their grade and impact on prognosis. In this article, we will discuss the current and developing uses of these imaging techniques including additional analysis using radiomics in the diagnosis and treatment of meningiomas, including treatment planning and prediction of tumor behavior.

Clinical utility of somatostatin receptor positron emission tomography imaging biomarkers for characterization of meningioma among incidental central nervous system lesions

OBJECTIVES

Somatostatin receptor (SSTR) PET imaging is utilized with increasing frequency in the clinical management of neuroendocrine tumors. Incidental PET-avid CNS lesions are commonly noted and presumed to be meningiomas. However, SSTR PET lacks specificity for meningioma identification. This study aimed to clarify the role of SSTR-based imaging in the classification of incidental CNS lesions based on current clinical practice.

METHODS

Patients who underwent both Ga-68-DOTATATE PET and brain MRI and had an incidental CNS lesion identified with a radiographic prediction of meningioma via one (discordant prediction) or both (concordant prediction) imaging modalities were retrospectively analyzed. Imaging indication, semiquantitative measures, and clinical history were recorded.

RESULTS

Among 48 patients with a CNS lesion identified on both imaging modalities, most scans were performed for a history of neuroendocrine tumor (64.6%). Cases with concordant lesion-type prediction of meningioma between imaging modalities ( N = 24) displayed a significantly higher SUV max (median 7.9 vs. 4.0; P = 0.008) and Krenning score (median 3.0 vs. 2.0; P = 0.005) on Ga-68-DOTATATE PET compared with cases with a discordant prediction of meningioma ( N = 24). In cases with lower SUV max values, Ga-68-DOTATATE was more likely to discordantly predict meningioma without agreement by the corresponding MRI. Prior cranial radiation or use of somatostatin mimetics did not affect quantitative radiographic measures, and MRI-based tumor size was similar across groups.

CONCLUSION

Lesions with increased avidity may be more confidently predicted as meningioma in Ga-68-DOTATATE PET scans, whereas there is more discrepancy in prediction among low SUV cases.

Differentiation of a Falcine Meningioma From Cerebral Venous Sinus Thrombosis Using DOTATATE PET

ABSTRACT

Differentiating brain tumors from nonneoplastic lesions using conventional MRI may be challenging. Clinical symptoms often remain unspecific, and imaging findings from MRI may be inconclusive. We present the case of a 23-year-old woman in whom an MRI suggested a cerebral venous sinus thrombosis. On the other hand, additional atypical MRI findings raised doubts regarding the initial diagnosis. Given the need for a diagnostic procedure with higher sensitivity and specificity for neoplastic tissue, PET with the radiolabeled somatostatin receptor ligand DOTATATE ( 68 Ga-DOTA- d -Phe1-Tyr3-octreotate) was performed. DOTATATE PET facilitated the diagnosis of a falcine meningioma consistent with its value for the differential diagnosis of meningioma.

Innovative treatments for meningiomas

Multi-recurrent high-grade meningiomas remain an unmet medical need in neuro-oncology when iterative surgeries and radiation therapy sessions fail to control tumor growth. Nevertheless, the last 10years have been marked by multiple advances in the comprehension of meningioma tumorigenesis via the discovery of new driver mutations, the identification of activated intracellular signaling pathways, and DNA methylation analyses, providing multiple potential therapeutic targets. Today, Anti-VEGF and mTOR inhibitors are the most used and probably the most active drugs in aggressive meningiomas. Peptide radioactive radiation therapy aims to target SSTR2A receptors, which are strongly expressed in meningiomas, but have an insufficient effect in most aggressive meningiomas, requiring the development of new techniques to increase the dose applied to the tumor. Based on the multiple potential intracellular targets, multiple targeted therapy clinical trials targeting Pi3K-Akt-mTOR and MAP kinase pathways as well as cell cycle and particularly, cyclin D4-6 are ongoing. Recently discovered driver mutations, SMO, Akt, and PI3KCA, offer new targets but are mostly observed in benign meningiomas, limiting their clinical relevance mainly to rare aggressive skull base meningiomas. Therefore, NF2 mutation remains the most frequent mutation and main challenging target in high-grade meningioma. Recently, inhibitors of focal adhesion kinase (FAK), which is involved in tumor cell adhesion, were tested in a phase 2 clinical trial with interesting but insufficient activity. The Hippo pathway was demonstrated to interact with NF2/Merlin and could be a promising target in NF2-mutated meningiomas with ongoing multiple preclinical studies and a phase 1 clinical trial. Recent advances in immune landscape comprehension led to the proposal of the use of immunotherapy in meningiomas. Except in rare cases of MSH2/6 mutation or high tumor mass burden, the activity of PD-1 inhibitors remains limited; however, its combination with various radiation therapy modalities is particularly promising. On the whole, therapeutic management of high-grade meningiomas is still challenging even with multiple promising therapeutic targets and innovations.

68Ga-DOTATOC PET in Extracranial Hepatic and Bone Metastasis of Atypical Refractory Meningioma: A Case Report

ABSTRACT

A falcine meningioma was diagnosed in a 66-year-old woman and was treated by surgery and 2 times by radiotherapy during 9 years of follow-up with the diagnosis of atypical meningioma. Three months after the last radiotherapy, incidental liver lesions were detected on chest CT realized for suspected pneumonia. In view of the predisposing factors for meningioma metastases, 68Ga-DOTATOC hepatic and cerebral PET/MRI was performed and completed by total body PET/CT demonstrating a somatostatin receptor 2 overexpression of the multiple liver lesions and several bone lesions. Biopsies from the liver and iliac bone confirmed the metastatic origin of meningioma.

Imaging Characteristics of Meningiomas

Contemporary neuroimaging of meningiomas has largely relied on computed tomography, and more recently magnetic resonance imaging. While these modalities are frequently used in nearly all clinical settings where meningiomas are treated for the routine diagnosis and follow-up of these tumors, advances in neuroimaging have provided novel opportunities for prognostication and treatment planning (including both surgical planning and radiotherapy planning). These include perfusion MRIs, and positron emission tomography (PET) imaging modalities. Here we will summarize the contemporary uses for neuroimaging in meningiomas, and future applications of novel, cutting edge imaging techniques that may be routinely implemented in the future to enable more precise treatment of these challenging tumors.

Immunohistochemical assessment and clinical, histopathologic, and molecular correlates of membranous somatostatin type-2A receptor expression in high-risk pediatric central nervous system tumors

INTRODUCTION

177Lu-DOTATATE, a radionuclide therapy that binds somatostatin type-2A receptors (SST2A), has demonstrated efficacy in neuroendocrine tumors and evidence of central nervous system (CNS) penetration, supporting potential expansion within pediatric neuro-oncology. Understanding the prevalence of SST2A expression across pediatric CNS tumors is essential to identify patients who may benefit from somatostatin receptor-targeted therapy and to further elucidate the oncogenic role of SST2A.

METHODS

SST2A immunohistochemistry (IHC) was performed on tumor specimens and interpreted by an experienced pathologist (blinded), utilizing semi-quantitative scoring of membranous expression within viable tumor. Immunoreactive cell percentage was visually scored as 0 (none), 1 (<10%), 2 (10-50%), 3 (51-80%), or 4 (>80%). Staining intensity was scored as 0 (none), 1 (weak), 2 (moderate), or 3 (strong). Combined scores for each specimen were calculated by multiplying percent immunoreactivity and staining intensity values (Range: 0-12).

RESULTS

A total of 120 tumor samples from 114 patients were analyzed. Significant differences in SST2A IHC scores were observed across histopathologic diagnoses, with consistently high scores in medulloblastoma (mean ± SD: 7.5 ± 3.6 [n=38]) and meningioma (5.7 ± 3.4 [n=15]), compared to minimal or absent expression in ATRT (0.3 ± 0.6 [n=3]), ETMR (1.0 ± 0 [n=3]), ependymoma (grades I-III; 0.2 ± 0.7 [n=27]), and high-grade glioma (grades III-IV; 0.4 ± 0.7 [n=23]). Pineoblastoma (3.8 ± 1.5 [n=4]) and other embryonal tumors (2.0 ± 4.0 [n=7]) exhibited intermediate, variable expression. Among medulloblastomas, SST2A IHC scores were higher in non-SHH (8.5 ± 3.1) than SHH (5.0 ± 3.3) molecular subgroups (p=0.033). In a subset of paired primary and recurrent specimens from four patients, SST2A IHC scores remained largely unchanged.

DISCUSSION

High membranous SST2A expression was demonstrated in medulloblastoma, meningioma, and some rarer embryonal tumors with potential diagnostic, biologic, and therapeutic implications. Somatostatin receptor-targeted therapy such as 177Lu-DOTATATE deserves further investigation in these highly SST2A-expressing pediatric CNS tumors.

Impact of SSTR PET on Inter-Observer Variability of Target Delineation of Meningioma and the Possibility of Using Threshold-Based Segmentations in Radiation Oncology

Aim: The aim of this study was to assess the effects of including somatostatin receptor agonist (SSTR) PET imaging in meningioma radiotherapy planning by means of changes in inter-observer variability (IOV). Further, the possibility of using threshold-based delineation approaches for semiautomatic tumor volume definition was assessed. Patients and Methods: Sixteen patients with meningioma undergoing fractionated radiotherapy were delineated by five radiation oncologists. IOV was calculated by comparing each delineation to a consensus delineation, based on the simultaneous truth and performance level estimation (STAPLE) algorithm. The consensus delineation was used to adapt a threshold-based delineation, based on a maximization of the mean Dice coefficient. To test the threshold-based approach, seven patients with SSTR-positive meningioma were additionally evaluated as a validation group. Results: The average Dice coefficients for delineations based on MRI alone was 0.84 ± 0.12. For delineation based on MRI + PET, a significantly higher dice coefficient of 0.87 ± 0.08 was found (p < 0.001). The Hausdorff distance decreased from 10.96 ± 11.98 mm to 8.83 ± 12.21 mm (p < 0.001) when adding PET for the lesion delineation. The best threshold value for a threshold-based delineation was found to be 14.0% of the SUVmax, with an average Dice coefficient of 0.50 ± 0.19 compared to the consensus delineation. In the validation cohort, a Dice coefficient of 0.56 ± 0.29 and a Hausdorff coefficient of 27.15 ± 21.54 mm were found for the threshold-based approach. Conclusions: SSTR-PET added to standard imaging with CT and MRI reduces the IOV in radiotherapy planning for patients with meningioma. When using a threshold-based approach for PET-based delineation of meningioma, a relatively low threshold of 14.0% of the SUVmax was found to provide the best agreement with a consensus delineation.

The Complementary Role of 68Ga-DOTATATE PET/CT in Diagnosis of Recurrent Meningioma

Introduction: Contrast-enhanced brain MRI is the choice of imaging modality in diagnosis and posttreatment evaluation, its role is limited in distinguishing recurrent lesion from postoperative change. 68Ga-DOTATATE is a somatostatin analog PET tracer which has high affinity to meningioma expressing somatostatin receptor. Methods and subjects: In this case series review, we described 8 patients with brain MRI suspected of recurrent meningioma who underwent focused 68Ga-DOTATATE PET/CT scan for radiation treatment planning. Results: The combined brain MRI and PET/CT allowed improved conspicuity of the lesions and aided radiation treatment planning. The time from the initial surgery to PET/CT scans varied widely ranging from 1 year to 12 years. Three patients had PET/CT shortly after the initial surgery (1-3 years) and underwent targeted radiation therapy. Subsequent imaging showed no evidence of recurrence. Four patients had prolonged time between the PET/CT and the initial surgery (7-12 years) which showed extensive tumor burden. All four patients expired shortly after the last PET/CT scan. Conclusion: 68Ga-DOTATATE PET shows promising complementary role in detection and treatment planning of recurrent meningioma.

Management of a Patient With Metastatic Gastrointestinal Neuroendocrine Tumor and Meningioma Submitted to Peptide Receptor Radionuclide Therapy With 177Lu-DOTATATE

ABSTRACT

A 76-year-old woman affected by pancreatic neuroendocrine tumor previously subjected to surgery with progressive liver disease and a concomitant mild symptomatic meningioma of the left pontocerebellar angle underwent 4 cycles of peptide receptor radionuclide therapy with 177Lu-DOTATATE. A prophylactic therapy with corticosteroids was carried out before each treatment cycle, and the neurosurgery unit was alerted in case of cerebral edema and related neurologic symptoms. A 68Ga-DOTATOC PET/CT scan performed after the completion of the 4 cycles' treatment documented a hepatic partial response and a substantial stability of the brain mass. No neurological complications occurred during treatment and follow-up.

Investigational PET tracers in neuro-oncology-What's on the horizon? A report of the PET/RANO group

Many studies in patients with brain tumors evaluating innovative PET tracers have been published in recent years, and the initial results are promising. Here, the Response Assessment in Neuro-Oncology (RANO) PET working group provides an overview of the literature on novel investigational PET tracers for brain tumor patients. Furthermore, newer indications of more established PET tracers for the evaluation of glucose metabolism, amino acid transport, hypoxia, cell proliferation, and others are also discussed. Based on the preliminary findings, these novel investigational PET tracers should be further evaluated considering their promising potential. In particular, novel PET probes for imaging of translocator protein and somatostatin receptor overexpression as well as for immune system reactions appear to be of additional clinical value for tumor delineation and therapy monitoring. Progress in developing these radiotracers may contribute to improving brain tumor diagnostics and advancing clinical translational research.

The Current Role of Peptide Receptor Radionuclide Therapy in Meningiomas

Meningiomas are the most common primary intracranial tumors. The majority of patients can be cured by surgery, or tumor growth can be stabilized by radiation. However, the management of recurrent and more aggressive tumors remains difficult because no established alternative treatment options exist. Therefore, innovative therapeutic approaches are needed. Studies have shown that meningiomas express somatostatin receptors. It is well known from treating neuroendocrine tumors that peptide radioreceptor therapy that targets somatostatin receptors can be effective. As yet, this therapy has been used for treating meningiomas only within individual curative trials. However, small case series and studies have demonstrated stabilization of the disease. Therefore, we see potential for optimizing this therapeutic option through the development of new substances and specific adaptations to the different meningioma subtypes. The current review provides an overview of this topic.

68Ga-DOTATATE PET-based Radiation Contouring Creates More Precise Radiation Volumes for Meningioma Patients

INTRODUCTION

Radiation treatment planning for meningiomas traditionally involves MRI contrast enhanced images to define residual tumor. However, the gross tumor volume may be difficult to delineate for patients with a meningioma in the skull base, sagittal sinus, or post resection. Advanced PET imaging using ⁶⁸Ga-DOTATATE PET, which has been shown to be more sensitive and specific than MRI imaging, can be used for target volume delineation in these circumstances. We hypothesize that ⁶⁸Ga-DOTATATE PET scan-based treatment planning will lead to smaller radiation volumes and will detect additional areas of disease compared to standard MRI alone.

METHODS

Our data evaluated retrospective, deidentified, and blinded gross tumor volume (GTV) contour delineation with 7 central nervous system (CNS) specialists (4 CNS radiation oncologists and 3 neuroradiologists) for 25 patients diagnosed with a meningioma who received both a ⁶⁸Ga-DOTATATE PET and an MRI for radiation treatment planning. Both the MRI and the PET were non-sequentially contoured by each physician for each patient.

RESULTS

The median MRI volume for each physician ranged from 16.94-25.53 ccs. The median PET volume for each physician ranged from 2.09-8.36 ccs. The median PET volume was smaller for each physician. In addition, 7/25 (28%) patients had new non-adjacent areas contoured on PET by at least 6 of the 7 physicians that were not contoured by these physicians on the corresponding MRI. These new areas would not have been in the traditional MRI based volumes.

CONCLUSION

Our study supports that ⁶⁸Ga-DOTATATE PET imaging may help radiation oncologists create more precise radiation treatment volumes through finding undetected areas of disease not seen on MRI. ⁶⁸Ga-DOTATATE PET guided treatment planning should be studied prospectively.

Somatostatin Receptor 2: A Potential Predictive Biomarker for Immune Checkpoint Inhibitor Treatment

Somatostatin receptor 2 (SSTR2), the most abundant receptor of somatostatin (SST), possesses immunoreactivity and is altered in many cancers. However, the association between SSTR2 and efficacy of immune checkpoint inhibitors (ICIs) has not yet been reported. Immunohistochemistry (IHC) information across 20 cancers was collected from the Human Protein Atlas (HPA) and used to analyze the expression of SSTR2. Immune signatures collected from public databases, such as BioCarta or Reactome, were used to investigate the association between SSTR2 and the tumor microenviroment in the Cancer Genome Atlas (TCGA). Data from cohorts treated with ICIs were collected to assess whether SSTR2 is associated with benefits from ICIs treatment. In the HPA, we found the SSTR2 IHC-positive rate of 13 cancers to be above 50%. Five types of cancer express SSTR2 mildly (positive rate: 25%-50%), while the remaining two types of cancer barely stained SSTR2-positive (positive rate: 0%-24%). In TCGA analysis, immune cell signatures and immune function pathways were enriched in high SSTR2 expression groups in most cancers. In each ICIs treated cohort, patients with high SSTR2 expression experienced numerically superior objective response rate (Braun: 14.8% vs 13.4%, p = 0.85; Gide: 69.4% vs 40.5%, p = 0.025; Mariathasan: 22.4% vs 16.7%, p = 0.233; Miao: 37.5% vs 11.8%; Riaz: 32.0% vs 7.7%, p = 0.067) and overall survival (Braun: HR (95%CI): 0.80 [0.62-1.04], p = 0.80; Gide: HR (95%CI): 0.61 [0.29-1.30], p = 0.20; Mariathasan: HR (95%CI): 0.83 [0.64-1.08], p = 0.16; Miao: HR (95%CI): 0.24 [0.086-0.65], p = 0.0028; Nathanson cohort: HR (95%CI): 0 [0-inf], p = 0.18; Riaz: HR (95%CI): 0.24 [0.086-0.65], p = 0.028) than patients with low SSTR2 expression. In pooled cohort, we found these differences were significant (Pool: 24.6% vs 16.7%, p = 0.0077; HR (95% CI): 0.77 [0.65-0.91], p = 0.0018). Our results suggest that SSTR2 is a potential predictive biomarker for response to ICIs.

Use of advanced neuroimaging and artificial intelligence in meningiomas

Anatomical cross‐sectional imaging methods such as contrast‐enhanced MRI and CT are the standard for the delineation, treatment planning, and follow‐up of patients with meningioma. Besides, advanced neuroimaging is increasingly used to non‐invasively provide detailed insights into the molecular and metabolic features of meningiomas. These techniques are usually based on MRI, e.g., perfusion‐weighted imaging, diffusion‐weighted imaging, MR spectroscopy, and positron emission tomography. Furthermore, artificial intelligence methods such as radiomics offer the potential to extract quantitative imaging features from routinely acquired anatomical MRI and CT scans and advanced imaging techniques. This allows the linking of imaging phenotypes to meningioma characteristics, e.g., the molecular‐genetic profile. Here, we review several diagnostic applications and future directions of these advanced neuroimaging techniques, including radiomics in preclinical models and patients with meningioma.

PET Imaging in Neuro-Oncology: An Update and Overview of a Rapidly Growing Area

Simple Summary

Positron emission tomography (PET) is a functional imaging technique which plays an increasingly important role in the management of brain tumors. Owing different radiotracers, PET allows to image different metabolic aspects of the brain tumors. This review outlines currently available PET radiotracers and their respective indications in neuro-oncology. It specifically focuses on the investigation of gliomas, meningiomas, primary central nervous system lymphomas as well as brain metastases. Recent advances in the production of PET radiotracers, image analyses and translational applications to peptide radionuclide receptor therapy, which allow to treat brain tumors with radiotracers, are also discussed. The objective of this review is to provide a comprehensive overview of PET imaging’s potential in neuro-oncology as an adjunct to brain magnetic resonance imaging (MRI).

Abstract

PET plays an increasingly important role in the management of brain tumors. This review outlines currently available PET radiotracers and their respective indications. It specifically focuses on ¹⁸F-FDG, amino acid and somatostatin receptor radiotracers, for imaging gliomas, meningiomas, primary central nervous system lymphomas as well as brain metastases. Recent advances in radiopharmaceuticals, image analyses and translational applications to therapy are also discussed. The objective of this review is to provide a comprehensive overview of PET imaging’s potential in neuro-oncology as an adjunct to brain MRI for all medical professionals implicated in brain tumor diagnosis and care.

Somatostatin Receptors in Human Meningiomas-Clinicopathological Aspects

Simple Summary

Meningioma diagnostics and grading are currently based on subjective histopathological criteria given by the 2016 World Health Organization (WHO) classification. However, biomarkers may provide a more objective approach to diagnostics. This study was designed to elucidate the diagnostic and prognostic value of somatostatin receptors (SSTRs) as biomarkers in meningiomas, which could help to identify patients with a higher risk of recurrence and provide more personalized treatment. We have confirmed, in a population of 162 patients, that SSTRs have diagnostic value and may aid in the differentiation between WHO grade 1 and grade 2 tumors. Furthermore, SSTR1, SSTR2 and SSTR5 were associated with higher malignancy grades. SSTR2 expression was found to be characteristic in meningiomas. To maintain objectiveness, we scoped for a digital evaluation of immunoreactivity. We aim to impact and motivate researchers to further investigations towards more objective criteria in meningioma diagnostics, which in turn will improve patient care.

Abstract

Meningiomas have high recurrence rates despite frequently benign histopathological appearances. Somatostatin receptors (SSTRs) may be reliable biomarkers that could identify patients with increased risk of recurrence. Even though SSTRs are previously detected in meningiomas, their associations to clinicopathological features remain unclear. The aim of this study was to investigate the diagnostic and prognostic value of SSTRs in a large series of human meningiomas with long follow-up data. Immunohistochemistry was used to measure the expression of SSTR1-SSTR5 in tissue samples from 162 patients diagnosed with intracranial meningiomas of World Health Organization (WHO) grade 1 or 2. Digital scoring and a manual staining index were applied to assess immunoreactivity. All SSTRs, except SSTR4, were upregulated in our series of meningiomas. SSTR1 (p = 0.036), SSTR2 (p = 0.036) and SSTR5 (p = 0.029) were associated with a higher malignancy grade. SSTR2 presented as the most reliable marker. Only SSTR2 was associated with time to recurrence (TTR) in univariate Cox regression analyses. Manual staining index was strongly correlated with digital scoring for all SSTRs (r > 0.65, p < 0.001). SSTRs, and especially SSTR2, are useful in the diagnostics of meningiomas, even though their prognostic value appears limited. Digital scoring is valuable to ensure reproducibility.

Peptide Receptor Radionuclide Therapy and Primary Brain Tumors: An Overview

Primary brain tumors (PBTs) are some of the most difficult types of cancer to treat, and despite advancements in surgery, chemotherapy and radiotherapy, new strategies for the treatment of PBTs are needed, especially for those with poor prognosis such as inoperable/difficult-to-reach lesions or relapsing disease. In regard to the last point, malignant primary brain tumors remain some of the most lethal types of cancer. Nuclear medicine may provide exciting new weapons and significant contributions in the treatment of PBTs. In this review, we performed literature research in order to highlight the possible role of peptide receptor radionuclide therapy (PRRT) in the treatment of PBTs with radiolabeled molecules that bind with high-affinity transmembrane receptors such as somatostatin receptors (SSTRs), neurokinin type-1 receptor and prostate-specific membrane antigen (PSMA). These receptors are overexpressed in some cancer types such as gliomas, meningiomas, pituitary tumors and medulloblastomas. A comprehensive overview of possible applications in this field will be shown, providing knowledge about benefits, feasibility, developments and limitations of PRRT in this type of tumor, also revealing new advantages in the management of the disease.

Theranostics in Brain Tumors

Theranostic nuclear oncology, mainly in neuro-oncology (neurotheranostics), aims to combine cancer imaging and therapy using the same targeting molecule. This approach tries to identify patients who are most likely to benefit from tumor molecular radionuclide therapy. The ability of radioneurotheranostic agents to interact with cancer cells at the molecular level with high specificity can significantly improve the effectiveness of cancer therapy. A variety of biologic targets are under investigation for treating brain tumors. PET-based precision imaging can substantially improve the therapeutic efficacy of radiotheranostic approach in brain tumors.

Differences in the expression of SSTR1-5 in meningiomas and its therapeutic potential

Beyond microsurgical resection and radiation therapy, there are currently no established treatment alternatives for meningioma patients. In selected cases, peptide radio receptor therapy (PRRT) can be implemented. For this purpose, a radionuclide is bound to a substance targeting specific receptors in meningiomas. One of them is somatostatin receptor 2, which can be found in most meningiomas. However, other somatostatin receptors (SSTR) exist, but their expressions have only been described in small case series. In this study, we analyzed the expression of SSTR1, 2A, 3, 4, and 5 in a large cohort of meningiomas in order to enable further refinement of this innovative treatment option. Overall, 726 tumor samples were processed into tissue microarrays and stained for SSTR1, 2A, 3, 4, and 5 immunohistochemically. Microscopic evaluation was done with an established semiquantitative score regarding percentual quantification and staining intensity, and results were correlated with clinical data. There was a significant lower rate of SSTR1 expression in meningiomas of male patients. Older age was associated with higher expression of SSTR1, 2A, and 5 and lower scores for SSTR3 and 4. Tumors treated with radiotherapy before resection showed lower rates of SSTR1 and 5 expression, while recurrent meningiomas had lower SSTR1 scores. Tumor tissue from patients suffering from neurofibromatosis type 2 had lower expression scores for SSTR1, 2, and 5. For SSTR3 and 4, NF2 patients showed higher scores than sporadic tumors. Spinal meningiomas had higher scores for SSTR1, 4, and 5 compared tumor location of the skull base and convexity/falx. Overall, higher WHO grade was associated with lower SSTR scores. While all SSTRs were expressed, there are marked differences of SSTR expression between meningioma subgroups. This has the potential to drive the development of more selective PRRT substances with higher treatment efficacy.

A Critical Review of PET Tracers Used for Brain Tumor Imaging

The brain is a common site for metastases as well as primary tumors. Although evaluation of these malignancies with contrast-enhanced MR imaging defines current clinical practice, ¹⁸F-fluorodeoxyglucose (FDG)-PET has shown considerable utility in this area. In addition, many other tracers targeting various aspects of tumor biology have been developed and tested. This article discusses recent developments in PET imaging and the anticipated role of FDG and other tracers in the assessment of brain tumors.

Primary and Secondary Optic Nerve Sheath Meningioma

Objective  This study was aimed to review issues relating to the recognition, radiographic diagnosis, monitoring, and management of primary and secondary optic nerve sheath meningioma (ONSM). Design  This study is a review of peer-reviewed literature combined with illustrative case studies. Participants and Methods  A literature search was conducted via the PubMed database using pertinent search terms. Selected articles were limited to those written or translated into English. Additional works cited within articles were also included. Individual cases were drawn from the experience of a tertiary academic neuroophthalmic and orbital practice. Tables summarize radiotherapeutic and surgical studies, excluding single case reports and studies focusing on meningioma of intracranial origin. Main Outcome Measurements  Review of reported surgical and radiotherapeutic series is the primary measurement. Results  The natural history of optic nerve sheath meningiomas is primarily characterized by progressive ipsilateral vision loss. Diagnosis is typically based on radiographic imaging findings, with biopsy remaining indicated in some patients. Management strategies may include observation, radiation, and/or surgical intervention, or a combination of these approaches. The role of surgery, especially with respect to primary ONSM (pONSM), remains controversial. Advancement of radiotherapy techniques has shifted modern treatment paradigms in pONSM toward radiation as primary treatment, as surgical outcomes are inferior in major studies. Although radiation remains the treatment of choice in many cases, selected patients may benefit from surgery, especially in the setting of secondary ONSM (sONSM). Conclusion  A wide variety of radiotherapeutic and surgical treatment modalities for ONSM exist. The specific indications for each management strategy continue to be redefined.

Clinical Significance of Somatostatin Receptor (SSTR) 2 in Meningioma

Somatostatin receptor (SSTR) 2, widely expressed in meningioma, is a G-protein-coupled receptor and can be activated by somatostatin or its synthetic analogs. SSTR2 is therefore extensively studied as a marker and target for the diagnosis and treatment of meningioma. Accumulating studies have revealed the crucial clinical significance of SSTR2 in meningioma. Summarizing the progress of these studies is urgently needed as it may not only provide novel and better management for patients with meningioma but also indicate the direction of future research. Pertinent literature is reviewed to summarize the recent collective knowledge and understanding of SSTR2’s clinical significance in meningioma in this review. SSTR2 offers novel ideas and approaches in the diagnosis, treatment, and prognostic prediction for meningioma, but more and further studies are required.

Simpson Grade Revisited – Intraoperative Estimation of the Extent of Resection in Meningiomas Versus Postoperative Somatostatin Receptor Positron Emission Tomography/Computed Tomography and Magnetic Resonance Imaging

BACKGROUND

Surgeon's intraoperative estimation of meningioma extent of resection (Simpson Grade, SG) is widely used as a prognostic factor for recurrence. However, the validity of SG is still a matter of debate. In preoperative imaging, 68Ga-DOTATATE/PET-CT has been shown to detect meningioma tissue even more sensitively than magnetic resonance imaging (MRI).

OBJECTIVE

To evaluate the Simpson grading within the framework of modern postoperative imaging techniques (MRI; PET-CT).

METHODS

At first, patients with WHO grade I meningioma, surgical resection, and postoperative 68Ga-DOTATATE/PET-CT within 6 mo after surgery were retrospectively analyzed. Second, an analogous prospective cohort of patients with WHO grade I meningioma was investigated by comparing SG after meningioma removal with postoperative MRI and 68Ga-DOTATATE/PET-CT within 6 mo after surgery.

RESULTS

A total of 37 patients were retrospectively analyzed. In total, 5/8 patients with SG-I and II resections showed tumor remnants according to postoperative PET-CT (SG 62.5% false negative). In the prospective cohort of 52 tumors, PET-CT displayed tracer uptake in 15/37 SG-I or II resections indicating unexpected tumor remnants (SG 40.5% false negative). MRI was false negative in 7 of these 15 cases (MRI 18.9% false negative) (P = .037). Discordant results according to PET-CT were more often found in convexity (40%) and falcine (46.7%) meningiomas than in skull base meningiomas (18.2%).

CONCLUSION

Intraoperative Simpson grading is at risk to underestimate tumor remnants, predominantly in grade I and II resections. Postoperative PET-CT improves detection rates compared to MRI. Prognostic impact of postoperative meningioma remnants according to PET-CT needs to be investigated prospectively.

Imaging and diagnostic advances for intracranial meningiomas

The archetypal imaging characteristics of meningiomas are among the most stereotypic of all central nervous system (CNS) tumors. In the era of plain film and ventriculography, imaging was only performed if a mass was suspected, and their results were more suggestive than definitive. Following more than a century of technological development, we can now rely on imaging to non-invasively diagnose meningioma with great confidence and precisely delineate the locations of these tumors relative to their surrounding structures to inform treatment planning. Asymptomatic meningiomas may be identified and their growth monitored over time; moreover, imaging routinely serves as an essential tool to survey tumor burden at various stages during the course of treatment, thereby providing guidance on their effectiveness or the need for further intervention. Modern radiological techniques are expanding the power of imaging from tumor detection and monitoring to include extraction of biologic information from advanced analysis of radiological parameters. These contemporary approaches have led to promising attempts to predict tumor grade and, in turn, contribute prognostic data. In this supplement article, we review important current and future aspects of imaging in the diagnosis and management of meningioma, including conventional and advanced imaging techniques using CT, MRI, and nuclear medicine.

68Ga-DOTATOC PET/CT in detecting neuroendocrine tumours responsible for initial or recurrent paraneoplastic Cushing's syndrome

PURPOSE

Paraneoplastic Cushing's syndrome (PCS) is frequently caused by neuroendocrine tumours (NETs). Approximately 20% of tumours are still occult years later. Gallium-68 somatostatin receptor-PET/CT is promising for the detection of the causal primary NET, but its role in case of recurrent PCS is rarely reported. We report our experience with DOTATOC PET/CT in localising the causal NET in cases of initial but also recurrent PCS, and its clinical impact.

METHODS

A retrospective review of all DOTATOC PET/CTs performed in consecutive patients referred for PCS to our centre, between January 2011 and June 2017, was done. Nineteen patients underwent 26 PET/CTs, 13 for detection of a primary NET, seven for persistent or recurrent PCS after resection, and six for surveillance after resection of NETs previously detected on a DOTATOC PET/CT in our centre.

RESULTS

Among the 13 PET/CTs performed to search for primary NET, five were positive: four carcinoid lung tumours were confirmed after resection and one lung focus was not confirmed since surgery would have carried a high risk. Clinical impact was 23% (3/13). Among the seven PET/CTs performed for persistent or recurrent PCS, six were true-positive, with confirmation of metastatic lymph nodes after resection. Clinical impact was 57% (4/7). All PET/CTs performed for surveillance were true-negative.

CONCLUSIONS

DOTATOC PET/CT seems to be a valuable tool for detection of the NET responsible for persistent or recurrent PCS after surgery. In this context, DOTATOC PET/CT was more effective than for the detection of the causal tumour in initial PCS.

Utilidad de la tomografía por emisión de positrones/tomografía computada (PET/CT) en pacientes con diagnóstico de meduloblastoma

"PET/CT (positron emission tomography/computed tomography, for its acronym in English) is a unique imaging method that provides in vivo evidence of both biochemical and physiological activities of the brain, spinal cord and tumors that involve these structures. Medulloblastoma is the most common malignant tumor of the central nervous system (CNS) in pediatric patients, so PET/CT plays an important role as it provides information on the grade and extent of the tumor as well as to determine the appropriate site for the biopsy, assessing the response to the treatment and the patient’s prognosis. There are different radiopharmaceuticals for the evaluation of central nervous system tumors, but 18F FDG (Fluor-2-fluoro-2-desoxy-D-glucose) and 68Ga-DOTA-NOC (68Ga-DOTA0-1NaI3-octreotide) have been studied to help us evaluate and follow up patients diagnosed with medulloblastoma. Medulloblastoma has an overexpression of glucose transporters, mainly type 1, and an overexpression of predominantly type 2 somatostatin receptors, which allows a high affinity for these radiopharmaceuticals. Key words: Medulloblastoma; positron emission tomography; PET/C; 18F-FDG; 68Ga-DOTA-NOC; brain tumor.

Somatostatin receptor expression and mTOR pathway activation in glioneuronal tumours of childhood

PURPOSE

To investigate the expression of somatostatin receptors (SSTRs) and markers of mTOR pathway in paediatric glioneuronal tumours and correlate these findings with tumour type, BRAFV600E mutational status and clinical characteristics such as tumour location, seizure frequency and duration, and age.

METHOD

37 children and adolescents with a neuropathological diagnosis of glioneuronal tumour were identified over a 22-year period. Immunohistochemical analyses for SSTRs type 1, 2A, 3, 5 and ezrin-radixin-moesin (ERM) and phosphorylated S6 (pS6), which are indicators of mTOR pathway activation, were performed in tumour specimens from 33 patients and evaluated using the immunoreactive score (IRS). The IRS were compared to tumour type, BRAFV600E status and clinical characteristics.

RESULTS

Ganglioglioma (GG) was the most frequently encountered subgroup (n = 27), followed by dysembryoplastic neuroepithelial tumour (DNET; n = 4). GGs expressed SSTR2A and SSTR3 to a high extent, 56 % and 44 % respectively. Expression of SSTR2A was also found in DNETs. Signs of mTOR pathway activation were abundant in GGs, but only present in one DNET. No correlations with BRAFV600E presence or clinical characteristics were found.

CONCLUSIONS

Expression of SSTRs and activation of mTOR pathway in paediatric glioneuronal tumour suggest that somatostatin analogues and mTOR inhibitors may have potential therapeutic implications in a subset of inoperable childhood glioneuronal tumours causing medically refractory epilepsy and/or tumour growth. Further clinical studies are warranted to validate these findings.

Benefits of re-do surgery for recurrent intracranial meningiomas

Meningiomas are the most common intracranial extra-axial tumor. While the literature is abundant on the therapeutic management of meningioma recurrence after the initial surgery, the natural history of repeated recurrences is poorly described, as well as and their respective management. A partly retrospective, partly prospective review was conducted in a Norwegian cohort of 1469 consecutive cases of meningioma surgically treated, totaling 11 414 patient-years of follow-up. 114 recurrences (7.7%) were treated surgically with a risk a surgical retreatment of 1% per patient-year of follow-up. 36 patients were operated on 3 times or more. The time-to-retreatment (TTR) decreased significantly and steadily between surgeries, from 4.3 ± 4 years after the first surgery to 2.4 ± 2.9 years after the third surgery. The primary driver for recurrence was the WHO grade (OR 7.13 [4.40;11.55], p < 0.001 for the first recurrence and OR 4.13 [1.49;12.15], p 0.008 for the second), the second predictive factor being a skull base location (OR 2.76 [1.95;3.99] p < 0.001 and OR 0.24 [0.09;0.65], p0.006 respectively). The rates of postoperative hematomas and infections were not influenced by the number of surgeries, whereas the rate of postoperative neurological worsening increased from 3.9% to 16.6% and 13.9%, respectively, after the first, second, and third surgeries. We observed that the TTR decreased significantly between surgeries in patients requiring repeated resections, indicating that surgical treatment of recurrences does not reset the clock but is indeed a "race against time". This should be considered when assessing the benefit-to-risk ratio of patients undergoing repeated surgeries for a recurrent meningioma.

An update on PET-based molecular imaging in neuro-oncology: challenges and implementation for a precision medicine approach in cancer care

PET imaging using novel radiotracers show promises for tumor grading and molecular characterization through visualizing molecular and functional properties of the tumors. Application of PET tracers in brain neoplasm depends on both type of the neoplasm and the research or clinical significance required to be addressed. In clinical neuro-oncology, 18F-FDG is used mainly to differentiate tumor recurrence from radiation-induced necrosis, and novel PET agents show attractive imaging properties. Novel PET tracers can offer biologic information not visible via contrast-enhanced MRI or 18F-FDG PET. This review aims to provide an update on the complementary role of PET imaging in neuro-oncology both in research and clinical settings along with presenting interesting cases in this context.

How we read: the combined use of MRI and novel PET tracers for the characterisation and treatment planning of masses in neuro-oncology

Technical advances in imaging are well demonstrated by MRI (Magnetic Resonance Imaging) and PET (Positron Emission Tomography). Excellent anatomical detail and a lack of ionising radiation make MRI the standard of care for most neuroimaging indications, and advanced sequences are providing an ever-growing ability for lesion characterisation. PET utilising the tracer fluorine-18 fluorodeoxyglucose is widely used in oncology, while newer PET tracers are able to target a growing number of metabolic pathways and cell membrane receptors. The sequential use of these modalities harnesses the strengths of both, providing complementary diagnostic and therapeutic information.Here we outline the ways in which we use MRI and PET in a complementary manner to improve lesion characterisation in neuro-oncology. Most commonly, an abnormality is detected on either PET or MRI, and the addition of the other modality allows a more confident diagnosis and/or demonstrates additional lesions, guiding treatment decisions and, in some cases, obviating the need for biopsy. These modalities may also be combined to guide the treatment of intracranial masses for which the diagnosis is known, such as neuro-endocrine tumour metastases or meningiomas refractory to conventional therapies.

Current status of PET imaging in neuro-oncology

Over the past decades, a variety of PET tracers have been used for the evaluation of patients with brain tumors. For clinical routine, the most important clinical indications for PET imaging in patients with brain tumors are the identification of neoplastic tissue including the delineation of tumor extent for the further diagnostic and therapeutic management (ie, biopsy, resection, or radiotherapy planning), the assessment of response to a certain anticancer therapy including its (predictive) effect on the patients’ outcome and the differentiation of treatment-related changes (eg, pseudoprogression and radiation necrosis) from tumor progression at follow-up. To serve medical professionals of all disciplines involved in the diagnosis and care of patients with brain tumors, this review summarizes the value of PET imaging for the latter-mentioned 3 clinically relevant indications in patients with glioma, meningioma, and brain metastases.