Treatment-Related Uptake of O-(2-18F-Fluoroethyl)-l-Tyrosine and l-[Methyl-3H]-Methionine After Tumor Resection in Rat Glioma Models

Detailed characterization of partial tumor resection in the Syngeneic Fischer/F98 Glioma Model

BACKGROUND

Preclinical models of brain tumors play a fundamental role in understanding tumor biology and deploying anti-tumor strategies. However, preclinical studies evaluate their potential therapy in tumor model without prior resection. Nevertheless, maximal safe resection, the first step in the clinical treatment of glioblastoma (GBM), is known to have a significant effect on adjuvant treatments.

NEW METHOD

We have therefore characterized two techniques to perform tumor resection in F98 glioma-bearing rats to bring this model closer to the clinical context. A total of 65 animals were assigned in 5 different groups: control, catheter (1.74 mm diameter) and biopsy punch (1.5/ 2.5/ 3 mm diameter). On day 10 post-tumor implantation, some animals were sacrificed on day 11 for histological analysis whereas the remaining animals were used for survival estimates.

RESULTS

All animals in the survival groups that underwent tumor resection recurred. The resection cavities were visible on the H&E histological sections. No significant difference was observed between the control and resection groups in term of survival but there was a trend towards improved survival with increasing tool diameter.

COMPARISON WITH EXISTING METHODS

Few studies have investigated the development of tumor resection models, but the majority of these techniques require sophisticated equipment. To our knowledge, we are the first to develop an easy-to-perform partial tumour resection model using the Fischer-F98 glioma model.

CONCLUSIONS

Here we present a detailed characterization of the tumor resection procedure and recurrence model, which has potential for the investigation of local delivery strategies in the treatment of GBM.

Deep mutual learning on hybrid amino acid PET predicts H3K27M mutations in midline gliomas

Predicting H3K27M mutation status in midline gliomas non-invasively is of considerable interest, particularly using deep learning with 11C-methionine (MET) and 18F-fluoroethyltyrosine (FET) positron emission tomography (PET). To optimise prediction efficiency, we derived an assistance training (AT) scheme to allow mutual benefits between MET and FET learning to boost the predictability but still only require either PET as inputs for predictions. Our method significantly surpassed conventional convolutional neural network (CNN), radiomics-based, and MR-based methods, achieved an area under the curve (AUC) of 0.9343 for MET, and an AUC of 0.8619 for FET during internal cross-validation (n = 90). The performance remained high in hold-out testing (n = 19) and consecutive testing cohorts (n = 21), with AUCs of 0.9205 and 0.7404. The clinical feasibility of the proposed method was confirmed by the agreements to multi-departmental decisions and outcomes in pathology-uncertain cases. The findings positions our method as a promising tool for aiding treatment decisions in midline glioma.

Ferroptosis in Glioma Immune Microenvironment: Opportunity and Challenge

Glioma is the most common intracranial malignant tumor in adults and the 5-year survival rate of glioma patients is extremely poor, even in patients who received Stupp treatment after diagnosis and this forces us to explore more efficient clinical strategies. At this time, immunotherapy shows great potential in a variety of tumor clinical treatments, however, its clinical effect in glioma is limited because of tumor immune privilege which was induced by the glioma immunosuppressive microenvironment, so remodeling the immunosuppressive microenvironment is a practical way to eliminate glioma immunotherapy resistance. Recently, increasing studies have confirmed that ferroptosis, a new form of cell death, plays an important role in tumor progression and immune microenvironment and the crosstalk between ferroptosis and tumor immune microenvironment attracts much attention. This work summarizes the progress studies of ferroptosis in the glioma immune microenvironment.

Prognostic Potential of Postoperative 18F-Fluorocholine PET/CT in Patients With High-Grade Glioma. Clinical Validation of FuMeGA Postoperative PET Criteria

OBJECTIVE

The aim of this study was to assess the prognostic performance of postoperative 18F-fluorocholine PET/CT in patients with high-grade glioma (HGG).

METHODS

Patients with HGG who underwent preoperative and postoperative 18F-fluorocholine PET/CT were prospectively enrolled in the study. Postoperative MRI was classified as complete versus incomplete resection. Postoperative 18F-fluorocholine PET/CT was classified as negative (complete) or positive for metabolic residual tumor (incomplete resection) using a 5-point score system. The correlation of positive locations on PET/CT with the sites of subsequent tumor recurrence was evaluated. The concordance of postoperative imaging techniques (Cohen κ) and their relation with progression-free survival and overall survival were assessed using Kaplan-Meier method and Cox regression analysis.

RESULTS

Fifty-one studies, belonging to 47 patients, were assessed. Four patients underwent 2 postoperative 18F-fluorocholine PET/CT scans as they needed a second tumor resection for recurrence. In the follow-up, 42 patients progressed, and 37 died. Concordance between postoperative PET/CT and MRI assessment was poor. Resection grade on MRI did not show any significant association with prognosis. In multivariate analysis, only age and postoperative PET/CT showed significant association with progression-free survival (hazard ratio [HR], 1.03 [1.01-1.06, P = 0.006] and 1.88 [0.96-3.71, P = 0.067], respectively) and overall survival (HR, 1.04 [1.01-1.07, P = 0.004] and 2.63 [1.22-5.68, P = 0.014], respectively). Postoperative positive 18F-fluorocholine PET/CT locations correlated with the sites of subsequent tumor recurrence in 81.82% of cases.

CONCLUSION

Postoperative 18F-fluorocholine PET/CT seems superior to postoperative MRI in the outcome prediction of patients with HGG, outperforming it in the identification of the most probable location of tumor recurrence.

Role of Molecular Imaging with PET/MR Imaging in the Diagnosis and Management of Brain Tumors

Gliomas are the most common primary brain tumors. Hybrid PET/MR imaging has revolutionized brain tumor imaging, allowing for noninvasive, simultaneous assessment of morphologic, functional, metabolic, and molecular parameters within the brain. Molecular information obtained from PET imaging may aid in the detection, classification, prognostication, and therapeutic decision making for gliomas. ¹⁸F-fluorodeoxyglucose (FDG) has been widely used in the setting of brain tumor imaging, and multiple techniques may be employed to optimize this methodology. More recently, a number of non-¹⁸F-FDG-PET radiotracers have been applied toward brain tumor imaging and are used in clinical practice.

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.

Current trends in the use of O-(2-[18F]fluoroethyl)-L-tyrosine ([18F]FET) in neurooncology

The diagnostic potential of PET using the amino acid analogue O-(2-[18F]fluoroethyl)-L-tyrosine ([18F]FET) in brain tumor diagnostics has been proven in many studies during the last two decades and is still the subject of multiple studies every year. In addition to standard magnetic resonance imaging (MRI), positron emission tomography (PET) using [18F]FET provides important diagnostic data concerning brain tumor delineation, therapy planning, treatment monitoring, and improved differentiation between treatment-related changes and tumor recurrence. The pharmacokinetics, uptake mechanisms and metabolism have been well described in various preclinical studies. The accumulation of [18F]FET in most benign lesions and healthy brain tissue has been shown to be low, thus providing a high contrast between tumor tissue and benign tissue alterations. Based on logistic advantages of F-18 labelling and convincing clinical results, [18F]FET has widely replaced short lived amino acid tracers such as L-[11C]methyl-methionine ([11C]MET) in many centers across Western Europe. This review summarizes the basic knowledge on [18F]FET and its contribution to the care of patients with brain tumors. In particular, recent studies about specificity, possible pitfalls, and the utility of [18F]FET PET in tumor grading and prognostication regarding the revised WHO classification of brain tumors are addressed.

Flare Phenomenon in O-(2-18F-Fluoroethyl)-l-Tyrosine PET After Resection of Gliomas

PET using O-(2-¹⁸F-fluoroethyl)-l-tyrosine (¹⁸F-FET) is useful to detect residual tumor tissue after glioma resection. Recent animal experiments detected reactive changes in ¹⁸F-FET uptake at the rim of the resection cavity within the first 2 wk after resection of gliomas. In the present study, we evaluated pre- and postoperative ¹⁸F-FET PET scans of glioma patients with particular emphasis on the identification of reactive changes after surgery. Methods: Forty-three patients with cerebral gliomas (9 low-grade, 34 high-grade; 9 primary tumors, 34 recurrent tumors) who had preoperative (time before surgery: median, 23 d; range, 6-44 d) and postoperative ¹⁸F-FET PET (time after surgery: median, 14 d; range, 5-28 d) were included. PET scans (20-40 min after injection) were evaluated visually for complete or incomplete resection and compared with MRI. Changes in ¹⁸F-FET uptake were evaluated by tumor-to-brain ratios in residual tumor and by maximum lesion-to-brain ratios near the resection cavity. Results: Visual analysis of ¹⁸F-FET PET scans revealed complete resection in 16 of 43 patients and incomplete resection in the remaining patients. PET results were concordant with MRI in 69% of the patients. The maximum lesion-to-brain ratio for ¹⁸F-FET uptake near the resection cavity was significantly higher than preoperative values (1.59 ± 0.36 vs. 1.14 ± 0.17; n = 43; P < 0.001). In 11 patients (26%), a flare phenomenon was observed, with a considerable increase in ¹⁸F-FET uptake compared with preoperative values in either the residual tumor (n = 5) or areas remote from the tumor on the preoperative PET scan (n = 6) (2.92 ± 1.24 vs. 1.62 ± 0.75; P < 0.001). Further follow-up in 5 patients showed decreasing ¹⁸F-FET uptake in the flare areas in 4 patients and progress in 1 patient. Conclusion: Our study confirmed that ¹⁸F-FET PET provides valuable information for assessing the success of glioma resection. Postoperative reactive changes at the rim of the resection cavity appear to be mild. However, in 23% of the patients, a postoperative flare phenomenon was observed that warrants further investigation.