18F-Fluciclovine PET to distinguish treatment-related effects from disease progression in recurrent glioblastoma: PET fusion with MRI guides neurosurgical sampling

Utility of [18F]fluciclovine PET/MRI for identifying the optimal biopsy target region, helping to avoid underdiagnosis in patients with glioblastoma: illustrative case

BACKGROUND

Glioblastoma (GBM) is known for its significant intratumoral heterogeneity, making biopsies susceptible to underdiagnosis if samples are taken from less malignant regions. [18F]Fluciclovine, a novel PET tracer, has demonstrated high accumulation in glioma tissue, with minimal uptake in normal brain tissue.

OBSERVATIONS

A 50-year-old woman presented with sensory aphasia. MRI revealed a FLAIR lesion extending from the left parietal to the medial temporal lobe. [18F]Fluciclovine PET/MRI identified two areas of increased uptake, both FLAIR negative. Stereotactic biopsy was used to obtain samples from PET-positive (PET+) and FLAIR-positive (FLAIR+) lesions. Pathological analysis of the PET+ lesion revealed densely proliferating tumor cells with irregularly enlarged nuclei, while the FLAIR+ lesion exhibited sparsely proliferating cells. Molecular analysis showed that both lesions were IDH wildtype with MGMT promoter hypomethylation. Sanger sequencing identified a telomerase reverse transcriptase promoter -124 C>T mutation in the PET+ lesion but not in the FLAIR+ lesion. The integrated diagnosis, based primarily on the PET+ lesion, was GBM, IDH wildtype.

LESSONS

This case highlights the importance of [18F]fluciclovine PET/MRI in identifying high-cell-density regions, minimizing the risk of underdiagnosis in GBM. Further studies are necessary to evaluate its prognostic value in GBM management. https://thejns.org/doi/10.3171/CASE24677.

Interleukin 6 and cancer resistance in glioblastoma multiforme

Despite unprecedented survival in patients with glioblastoma (GB), the aggressive primary brain cancer remains largely incurable and its mechanisms of treatment resistance have gained particular attention. The cytokine interleukin 6 (IL-6) and its receptor weave through the hallmarks of malignant gliomas and may represent a key vulnerability to GB. Known for activating the STAT3 pathway in autocrine fashion, IL-6 is amplified in GB and has been recognized as a negative biomarker for GB prognosis, rendering it a putative target of novel GB therapies. While it has been recognized as a biologically active component of GB for three decades only with concurrent advances in understanding of complementary immunotherapy has the concept of targeting IL-6 for a human clinical trial gained scientific footing.

Circulating biomarkers literature in glioma patient populations

Liquid biopsy, the process of identifying circulating biomarkers in patients with cancer, has emerged as clinically significant in population screening, tumor status & subclassification, and individualized patient treatment from tumor genotyping. While advances in genome sequencing and mass spectrometry have yielded large datasets available for mining and identified promising biomarkers in breast, melanoma, and lung cancers, among others, challenges persist in identifying biomarkers in neuro-oncology. Despite growing efforts in biomarker research and promise in their emergent clinical potential, there presently exists no validated circulating biomarker test for patients presenting with gliomas, the most common primary brain cancer.

Pseudoprogression versus true progression in glioblastoma: what neurosurgeons need to know

Management of patients with glioblastoma (GBM) is complex and involves implementing standard therapies including resection, radiation therapy, and chemotherapy, as well as novel immunotherapies and targeted small-molecule inhibitors through clinical trials and precision medicine approaches. As treatments have advanced, the radiological and clinical assessment of patients with GBM has become even more challenging and nuanced. Advances in spatial resolution and both anatomical and physiological information that can be derived from MRI have greatly improved the noninvasive assessment of GBM before, during, and after therapy. Identification of pseudoprogression (PsP), defined as changes concerning for tumor progression that are, in fact, transient and related to treatment response, is critical for successful patient management. These temporary changes can produce new clinical symptoms due to mass effect and edema. Differentiating this entity from true tumor progression is a major decision point in the patient's management and prognosis. Providers may choose to start an alternative therapy, transition to a clinical trial, consider repeat resection, or continue with the current therapy in hopes of resolution. In this review, the authors describe the invasive and noninvasive techniques neurosurgeons need to be aware of to identify PsP and facilitate surgical decision-making.

18F-fluciclovine PET/CT to distinguish radiation necrosis from tumor progression for brain metastases treated with radiosurgery: results of a prospective pilot study

PURPOSE

Distinguishing radiation necrosis from tumor progression among patients with brain metastases previously treated with stereotactic radiosurgery represents a common diagnostic challenge. We performed a prospective pilot study to determine whether PET/CT with 18F-fluciclovine, a widely available amino acid PET radiotracer, repurposed intracranially, can accurately diagnose equivocal lesions.

METHODS

Adults with brain metastases previously treated with radiosurgery presenting with a follow-up tumor-protocol MRI brain equivocal for radiation necrosis versus tumor progression underwent an 18F-fluciclovine PET/CT of the brain within 30 days. The reference standard for final diagnosis consisted of clinical follow-up until multidisciplinary consensus or tissue confirmation.

RESULTS

Of 16 patients imaged from 7/2019 to 11/2020, 15 subjects were evaluable with 20 lesions (radiation necrosis, n = 16; tumor progression, n = 4). Higher SUVmax statistically significantly predicted tumor progression (AUC = 0.875; p = 0.011). Lesion SUVmean (AUC = 0.875; p = 0.018), SUVpeak (AUC = 0.813; p = 0.007), and SUVpeak-to-normal-brain (AUC = 0.859; p = 0.002) also predicted tumor progression, whereas SUVmax-to-normal-brain (p = 0.1) and SUVmean-to-normal-brain (p = 0.5) did not. Qualitative visual scores were significant predictors for readers 1 (AUC = 0.750; p < 0.001) and 3 (AUC = 0.781; p = 0.045), but not for reader 2 (p = 0.3). Visual interpretations were significant predictors for reader 1 (AUC = 0.898; p = 0.012) but not for reader 2 (p = 0.3) or 3 (p = 0.2).

CONCLUSIONS

In this prospective pilot study of patients with brain metastases previously treated with radiosurgery presenting with a contemporary MRI brain with a lesion equivocal for radiation necrosis versus tumor progression, 18F-fluciclovine PET/CT repurposed intracranially demonstrated encouraging diagnostic accuracy, supporting the pursuit of larger clinical trials which will be necessary to establish diagnostic criteria and performance.

The Role of Hypoxia and Cancer Stem Cells in Development of Glioblastoma

Glioblastoma multiform (GBM) is recognized as the most malignant brain tumor with a high level of hypoxia, containing a small population of glioblastoma stem like cells (GSCs). These GSCs have the capacity of self-renewal, proliferation, invasion and recapitulating the parent tumor, and are major causes of radio-and chemoresistance of GBM. Upregulated expression of hypoxia inducible factors (HIFs) in hypoxia fundamentally contributes to maintenance and progression of GSCs. Therefore, we thoroughly reviewed the currently acknowledged roles of hypoxia-associated GSCs in development of GBM. In detail, we recapitulated general features of GBM, especially GSC-related features, and delineated essential responses resulted from interactions between GSC and hypoxia, including hypoxia-induced signatures, genes and pathways, and hypoxia-regulated metabolic alterations. Five hypothesized GSC niches are discussed and integrated into one comprehensive concept: hypoxic peri-arteriolar niche of GSCs. Autophagy, another protective mechanism against chemotherapy, is also closely related to hypoxia and is a potential therapeutic target for GBM. In addition, potential causes of therapeutic resistance (chemo-, radio-, surgical-, immuno-), and chemotherapeutic agents which can improve the therapeutic effects of chemo-, radio-, or immunotherapy are introduced and discussed. At last, as a potential approach to reverse the hypoxic microenvironment in GBM, hyperbaric oxygen therapy (HBOT) might be an adjuvant therapy to chemo-and radiotherapy after surgery. In conclusion, we focus on demonstrating the important role of hypoxia on development of GBM, especially by affecting the function of GSCs. Important advantages have been made to understand the complicated responses induced by hypoxia in GBM. Further exploration of targeting hypoxia and GSCs can help to develop novel therapeutic strategies to improve the survival of GBM patients.

How Can We Optimize the Value Assessment and Appraisal of Orphan Drugs for Reimbursement Purposes? A Qualitative Interview Study Across European Countries

Introduction: The expansion of orphan drug treatment at increasing prices, together with uncertainties regarding their (cost-)effectiveness raises difficulties for decision-makers to assess these drugs for reimbursement. The present qualitative study aims to gain better insight into current value assessment and appraisal frameworks for orphan drugs, and provides guidance for improvement. Methods: 22 European experts from 19 different countries were included in a qualitative survey, followed by in-depth semi-structured interviews. These experts were academics, members of reimbursement agencies or health authorities, or members of regulatory or health/social insurance institutions. Adopting a Grounded Theory approach, transcripts were analysed according to the QUAGOL method, supported by the qualitative data analysis software Nvivo. Results: Although participants indicated several good practices (e.g., the involvement of patients and the presence of structure and consistency), several barriers (e.g., the lack of transparency) lead to questions regarding the efficiency of the overall reimbursement process. In addition, the study identified a number of "contextual" determinants (e.g., bias, perverse effects of the orphan drug legislation, and an inadequate consideration of the opportunity cost), which may undermine the legitimacy of orphan drug reimbursement decisions. Conclusion: The present study provides guidance for decision-makers to improve the efficiency of orphan drug reimbursement. In particular, decision-makers can generate quick wins by limiting the impact of contextual determinants rather than improving the methods included in the HTA. When implemented into a framework that promotes "Accountability for Reasonableness" (A4R), this allows decision-makers to improve the legitimacy of reimbursement decisions concerning future orphan drugs.

PET/MRI in Pediatric Neuroimaging: Primer for Clinical Practice

Modern pediatric imaging seeks to provide not only exceptional anatomic detail but also physiologic and metabolic information of the pathology in question with as little radiation penalty as possible. Hybrid PET/MR imaging combines exquisite soft-tissue information obtained by MR imaging with functional information provided by PET, including metabolic markers, receptor binding, perfusion, and neurotransmitter release data. In pediatric neuro-oncology, PET/MR imaging is, in many ways, ideal for follow-up compared with PET/CT, given the superiority of MR imaging in neuroimaging compared with CT and the lower radiation dose, which is relevant in serial imaging and long-term follow-up of pediatric patients. In addition, although MR imaging is the main imaging technique for the evaluation of spinal pathology, PET/MR imaging may provide useful information in several clinical scenarios, including tumor staging and follow-up, treatment response assessment of spinal malignancies, and vertebral osteomyelitis. This review article covers neuropediatric applications of PET/MR imaging in addition to considerations regarding radiopharmaceuticals, imaging protocols, and current challenges to clinical implementation.

Neuro-Oncology Practice Clinical Debate: FDG PET to differentiate glioblastoma recurrence from treatment-related changes

The ability to accurately differentiate treatment-related changes (ie, pseudoprogression and radiation necrosis) from recurrent glioma remains a critical diagnostic problem in neuro-oncology. Because these entities are treated differently and have vastly different outcomes, accurate diagnosis is necessary to provide optimal patient care. In current practice, this diagnostic quandary commonly requires either serial imaging or histopathologic tissue confirmation. In this article, experts in the field debate the utility of 2-deoxy-2[18F]fluoro-d-glucose positron emission tomography (FDG PET) as an imaging tool to distinguish tumor recurrence from treatment-related changes in a patient with glioblastoma and progressive contrast enhancement on magnetic resonance (MR) following chemoradiotherapy.

A perspective on the radiopharmaceutical requirements for imaging and therapy of glioblastoma

Despite numerous clinical trials and pre-clinical developments, the treatment of glioblastoma (GB) remains a challenge. The current survival rate of GB averages one year, even with an optimal standard of care. However, the future promises efficient patient-tailored treatments, including targeted radionuclide therapy (TRT). Advances in radiopharmaceutical development have unlocked the possibility to assess disease at the molecular level allowing individual diagnosis. This leads to the possibility of choosing a tailored, targeted approach for therapeutic modalities. Therapeutic modalities based on radiopharmaceuticals are an exciting development with great potential to promote a personalised approach to medicine. However, an effective targeted radionuclide therapy (TRT) for the treatment of GB entails caveats and requisites. This review provides an overview of existing nuclear imaging and TRT strategies for GB. A critical discussion of the optimal characteristics for new GB targeting therapeutic radiopharmaceuticals and clinical indications are provided. Considerations for target selection are discussed, i.e. specific presence of the target, expression level and pharmacological access to the target, with particular attention to blood-brain barrier crossing. An overview of the most promising radionuclides is given along with a validation of the relevant radiopharmaceuticals and theranostic agents (based on small molecules, peptides and monoclonal antibodies). Moreover, toxicity issues and safety pharmacology aspects will be presented, both in general and for the brain in particular.

Contribution of PET imaging to radiotherapy planning and monitoring in glioma patients - a report of the PET/RANO group

The management of patients with glioma usually requires multimodality treatment including surgery, radiotherapy, and systemic therapy. Accurate neuroimaging plays a central role for radiotherapy planning and follow-up after radiotherapy completion. In order to maximize the radiation dose to the tumor and to minimize toxic effects on the surrounding brain parenchyma, reliable identification of tumor extent and target volume delineation is crucial. The use of positron emission tomography (PET) for radiotherapy planning and monitoring in gliomas has gained considerable interest over the last several years, but Class I data are not yet available. Furthermore, PET has been used after radiotherapy for response assessment and to distinguish tumor progression from pseudoprogression or radiation necrosis. Here, the Response Assessment in Neuro-Oncology (RANO) working group provides a summary of the literature and recommendations for the use of PET imaging for radiotherapy of patients with glioma based on published studies, constituting levels 1-3 evidence according to the Oxford Centre for Evidence-based Medicine.

Tumor recurrence or treatment-related changes following chemoradiation in patients with glioblastoma: does pathology predict outcomes?

BACKGROUND

Despite surgical resection and chemoradiation, all patients with GBM invariably recur. Radiological imaging is limited in differentiating tumor recurrence (TR) from treatment-related changes (TRC); therefore, re-resection is often needed. Few studies have assessed the relationship between re-resection histopathology and overall survival (OS). We performed a large retrospective study to analyze the clinical significance of histopathology following re-resection and its influence on genomic sequencing results.

METHODS

Clinical, radiographic, and histological information was compiled from 675 patients with GBM (2005-2017). 137-patients met the inclusion criteria. IDH1 p.R132H immunohistochemistry was performed in all patients. Next-generation sequencing interrogating 205 tumor-related genes was performed in 68-patients. Molecular alterations from initial and subsequent resections were compared in a subset of cases.

RESULTS

There were no differences in OS (17.3-months TRC vs. 21-months TR, p = 0.881) and survival from progression (9.0 vs. 11.7-months, p = 0.778) between patients with TR and TRC on re-resection. TR patients were more likely to receive salvage radiotherapy (26% vs. 0%) and tumor-treating fields (25% vs. 5%,) after the 2nd surgery than the TRC group (p = < 0.045). There was no correlation between mutations and TRC. IDH status was not predictive of TRC. Fifteen-patients had sequencing results from multiple surgeries without evident differences in genomic alterations.

CONCLUSIONS

Histopathologic findings following chemoradiation do not correlate with clinical outcomes. Such findings should be considered during patient management and clinical trial enrollment. Standardization of tissue sampling and interpretation following reoperation is urgently needed. Future work is required to understand the relationship between the mutation profile following TRC and outcomes.

Molecular and Cellular Complexity of Glioma. Focus on Tumour Microenvironment and the Use of Molecular and Imaging Biomarkers to Overcome Treatment Resistance

This review highlights the importance and the complexity of tumour biology and microenvironment in the progression and therapy resistance of glioma. Specific gene mutations, the possible functions of several non-coding microRNAs and the intra-tumour and inter-tumour heterogeneity of cell types contribute to limit the efficacy of the actual therapeutic options. In this scenario, identification of molecular biomarkers of response and the use of multimodal in vivo imaging and in particular the Positron Emission Tomography (PET) based molecular approach, can help identifying glioma features and the modifications occurring during therapy at a regional level. Indeed, a better understanding of tumor heterogeneity and the development of diagnostic procedures can favor the identification of a cluster of patients for personalized medicine in order to improve the survival and their quality of life.

Current Landscape and Emerging Fields of PET Imaging in Patients with Brain Tumors

The number of positron-emission tomography (PET) tracers used to evaluate patients with brain tumors has increased substantially over the last years. For the management of patients with brain tumors, the most important indications are the delineation of tumor extent (e.g., for planning of resection or radiotherapy), the assessment of treatment response to systemic treatment options such as alkylating chemotherapy, and the differentiation of treatment-related changes (e.g., pseudoprogression or radiation necrosis) from tumor progression. Furthermore, newer PET imaging approaches aim to address the need for noninvasive assessment of tumoral immune cell infiltration and response to immunotherapies (e.g., T-cell imaging). This review summarizes the clinical value of the landscape of tracers that have been used in recent years for the above-mentioned indications and also provides an overview of promising newer tracers for this group of patients.