Brain PET/CT using prostate cancer radiopharmaceutical agents in the evaluation of gliomas

Prostate-Specific Membrane Antigen Use in Glioma Management: Past, Present, and Future

BACKGROUND

Prostate-specific membrane antigen (PSMA) is a membrane-bound metallopeptidase highly expressed in the neovasculature of many solid tumors including gliomas. It is a particularly enticing therapeutic target due to its ability to internalize, thereby delivering radioligands or pharmaceuticals to the intracellular compartment. Targeting the neovasculature of gliomas using PSMA for diagnosis and management has been a recent area of increased study and promise. The purpose of this review is to synthesize the current state and future directions of PSMA use in the histopathologic study, imaging, and treatment of gliomas.

METHODS

PubMed and Scopus databases were used to conduct a literature review on PSMA use in gliomas in June 2023. Terms searched included "PSMA," "Prostate-Specific Membrane Antigen" OR "PSMA" OR "PSMA PET" AND "glioma" OR "high grade glioma" OR "glioblastoma" OR "GBM."

RESULTS

Ninety-four publications were screened for relevance with 61 studies, case reports, and reviews being read to provide comprehensive context for the historical, contemporary, and prospective use of PSMA in glioma management.

CONCLUSIONS

PSMA PET imaging is currently a promising and accurate radiographic tool for the diagnosis and management of gliomas. PSMA histopathology likely represents a viable tool for helping predict glioma behavior. More studies are needed to investigate the role of PSMA-targeted therapeutics in glioma management, but preliminary reports have indicated its potential usefulness in treatment.

Prostate-Specific Membrane Antigen Positron Emission Tomography Oncological Applications beyond Prostate Cancer in Comparison to Other Radiopharmaceuticals

BACKGROUND

Prostate-specific membrane antigen (PSMA) is a type II transmembrane glycoprotein overexpressed on the surface of tumor cells in most of the patients affected by prostate adenocarcinoma (PCa). However, PSMA expression has also been demonstrated in the endothelial cells of newly formed vessels of various solid tumors, suggesting a role for PSMA in neoangiogenesis. In this scenario, gallium-68 (68Ga) or fluoro-18 (18F)-labeled PSMA positron emission tomography (PET) may play a role in tumors other than PCa, generally evaluated employing other radiopharmaceuticals targeting different pathways. This review aims to investigate the detection rate of PSMA-PET compared to other radiopharmaceuticals (especially [18F]FDG) in non-prostate tumors to identify patients who may benefit from the use of such a theragnostic agent.

METHODS

We performed a bibliographic search on three different databases until February 2024 using the following terms: "positron emission tomography", "PET", "PET/CT", "Prostate-specific membrane antigen", "PSMA", "non-prostate", "not prostate cancer", "solid tumor", "FDG", "Fluorodeoxyglucose", "FAPi", "FET", "MET", "DOPA", "choline", "FCH", "FES", "DOTATOC", "DOTANOC", and "DOTATATE". Only original articles edited in English with at least 10 patients were included.

RESULTS

Out of a total of 120 articles, only 25 original articles comparing PSMA with other radiotracers were included in this study. The main evidence was demonstrated in renal cell carcinoma, where PSMA showed a higher detection rate compared to [18F]FDG PET/CT, with implications for patient management. PSMA PET may also improve the assessment of other entities, such as gliomas, in defining regions of early neoangiogenesis. Further data are needed to evaluate the potential role of PSMA-PET in triple-negative breast cancer as a novel therapeutic vascular target. Finally, unclear applications of PSMA-PET include thyroid and gastrointestinal tumors.

CONCLUSIONS

The present review shows the potential use of PSMA-labeled PET/CT in solid tumors beyond PCa, underlining its value over other radiopharmaceuticals (mainly [18F]FDG). Prospective clinical trials with larger sample sizes are crucial to further investigate these possible clinical applications.

[11C]Choline PET/CT in a Patient with Prostate Cancer Biochemical Recurrence Showing Two Suspicious Findings in the Breast and Liver

A 79-year-old man with prostate cancer (PCa) was referred to our center to perform a [11C]Choline PET/CT for biochemical recurrence. Positron emission tomography/computed tomography (PET/CT) scan detected PCa recurrence in the prostate gland and several pelvic and abdominal lymph nodes. Two abnormal uptakes were also identified in the right breast and in the liver, respectively. Breast histological findings turned out to be gynecomastia, while the liver lesion resulted in a benign perfusion anomaly at follow-up magnetic resonance imaging (MRI). Although incidental findings were benign in this case, it is important to always investigate abnormal uptakes of [11C]Choline, as it could be an expression of further metastases or synchronous malignancies such as breast cancer and hepatocellular carcinoma.

Prostate Cancer Biochemical Recurrence Resulted Negative on [68Ga]Ga-PSMA-11 but Positive on [18F]Fluoromethylcholine PET/CT

For prostate cancer (PCa) biochemical recurrence (BCR), the primarily suggested imaging technique by the European Association of Urology (EAU) guidelines is prostate-specific membrane antigen (PSMA) positron emission tomography/computer tomography (PET/CT). Indeed, the increased detection rate of PSMA PET/CT for early BCR has led to a fast and wide acceptance of this novel technology. However, PCa is a very heterogeneous disease, not always easily assessable with the highly specific PSMA PET with around 10% of cases occuring without PSMA expression. In this paper, we present the case of a patient with PCa BCR that resulted negative on [⁶⁸Ga]Ga-PSMA-11 PET/CT, but positive on [¹⁸F]Fluoromethylcholine (Choline) PET/CT.

[68Ga]Ga-PSMA PET/MRI, histological PSMA expression and preliminary experience with [177Lu]Lu-PSMA therapy in relapsing high-grade glioma

Purpose

High-grade gliomas (HGG) are still associated with a dismal prognosis. Prostate specific membrane antigen (PSMA) is discussed as a theranostic target for PSMA-directed radioligand therapy ([¹⁷⁷Lu]Lu-PSMA RLT). Here, we report on the correlation of [⁶⁸Ga]Ga-PSMA uptake with histological PSMA expression and on our preliminary experience with [¹⁷⁷Lu]Lu-PSMA RLT in relapsing HGG.

Methods

Patients with relapsing HGG underwent [⁶⁸Ga]Ga-PSMA PET/MRI to evaluate eligibility for an individualized treatment approach with [¹⁷⁷Lu]Lu-PSMA. Standard uptake values (SUV) for tumor and liver and respective tumor-to-background ratios (compared to the liver) (TBR) on [⁶⁸Ga]Ga-PSMA PET/MRI were assessed. Eligibility criteria for [¹⁷⁷Lu]Lu-PSMA therapy were exhaustion of all standard treatment options available and TBR_max>1.0. In 11 samples, immunohistochemical PSMA expression was determined, quantified using the H-score and correlated with uptake on [⁶⁸Ga]Ga-PSMA PET/MRI.

Results

We included 20 patients with a median age of 53 years (IQR 42-57). The median SUV on [⁶⁸Ga]Ga-PSMA PET/MRI was 4.5 (3.7-6.2) for SUV_max and 1.4 (1.1-1.7) for SUV_mean. The respective TBR was maximum 0.6 (0.4-0.8) and mean 0.3 (0.2-0.4). High TBR_max correlated with increased endothelial PSMA expression [H-score of 65 (62.5-77.5)]. Three patients (15%) presented a TBR_max>1.0 and qualified for [¹⁷⁷Lu]Lu-PSMA RLT. No treatment related toxicity was observed.

Conclusion

Only a minority of patients with relapsing HGG qualified for [¹⁷⁷Lu]Lu-PSMA RLT. Our data demonstrates that PSMA expression in the neo-vasculature corresponds to PSMA uptake on [⁶⁸Ga]Ga-PSMA PET/MRI and might be used as a screening tool for patient selection. Future prospective studies need to focus the debate on TBR_max thresholds as inclusion criteria for PSMA RLT.

Intracranial Solitary Fibrous Tumor: A "New" Challenge for PET Radiopharmaceuticals

Solitary fibrous tumor (SFT) of the central nervous system, previously named and classified with the term hemangiopericytoma (HPC), is rare and accounts for less than 1% of all intracranial tumors. Despite its benign nature, it has a malignant behavior due to the high rate of recurrence and distant metastasis, occurring in up to 50% of cases. Surgical resection of the tumor is the treatment of choice. Radiotherapy represents the gold standard in the case of post-surgery residual disease, relapse, and distant metastases. In this context, imaging plays a crucial role in identifying the personalized therapeutic decision for each patient. Although the referring imaging approach in SFT is morphologic, an emerging role of positron emission tomography (PET) has been reported in the literature. However, there is still a debate on which radiotracers have the best accuracy for studying these uncommon tumors because of the histological or biological heterogeneity of SFT.

Feasibility on the Use of Radiomics Features of 11[C]-MET PET/CT in Central Nervous System Tumours: Preliminary Results on Potential Grading Discrimination Using a Machine Learning Model

Background/Aim: Nowadays, Machine Learning (ML) algorithms have demonstrated remarkable progress in image-recognition tasks and could be useful for the new concept of precision medicine in order to help physicians in the choice of therapeutic strategies for brain tumours. Previous data suggest that, in the central nervous system (CNS) tumours, amino acid PET may more accurately demarcate the active disease than paramagnetic enhanced MRI, which is currently the standard method of evaluation in brain tumours and helps in the assessment of disease grading, as a fundamental basis for proper clinical patient management. The aim of this study is to evaluate the feasibility of ML on 11[C]-MET PET/CT scan images and to propose a radiomics workflow using a machine-learning method to create a predictive model capable of discriminating between low-grade and high-grade CNS tumours. Materials and Methods: In this retrospective study, fifty-six patients affected by a primary brain tumour who underwent 11[C]-MET PET/CT were selected from January 2016 to December 2019. Pathological examination was available in all patients to confirm the diagnosis and grading of disease. PET/CT acquisition was performed after 10 min from the administration of 11C-Methionine (401–610 MBq) for a time acquisition of 15 min. 11[C]-MET PET/CT images were acquired using two scanners (24 patients on a Siemens scan and 32 patients on a GE scan). Then, LIFEx software was used to delineate brain tumours using two different semi-automatic and user-independent segmentation approaches and to extract 44 radiomics features for each segmentation. A novel mixed descriptive-inferential sequential approach was used to identify a subset of relevant features that correlate with the grading of disease confirmed by pathological examination and clinical outcome. Finally, a machine learning model based on discriminant analysis was used in the evaluation of grading prediction (low grade CNS vs. high-grade CNS) of 11[C]-MET PET/CT. Results: The proposed machine learning model based on (i) two semi-automatic and user-independent segmentation processes, (ii) an innovative feature selection and reduction process, and (iii) the discriminant analysis, showed good performance in the prediction of tumour grade when the volumetric segmentation was used for feature extraction. In this case, the proposed model obtained an accuracy of ~85% (AUC ~79%) in the subgroup of patients who underwent Siemens tomography scans, of 80.51% (AUC 65.73%) in patients who underwent GE tomography scans, and of 70.31% (AUC 64.13%) in the whole patients’ dataset (Siemens and GE scans). Conclusions: This preliminary study on the use of an ML model demonstrated to be feasible and able to select radiomics features of 11[C]-MET PET with potential value in prediction of grading of disease. Further studies are needed to improve radiomics algorithms to personalize predictive and prognostic models and potentially support the medical decision process.

Imaging and treatment of brain tumors through molecular targeting: Recent clinical advances

Molecular imaging techniques have rapidly progressed over recent decades providing unprecedented in vivo characterization of metabolic pathways and molecular biomarkers. Many of these new techniques have been successfully applied in the field of neuro-oncological imaging to probe tumor biology. Targeting specific signaling or metabolic pathways could help to address several unmet clinical needs that hamper the management of patients with brain tumors. This review aims to provide an overview of the recent advances in brain tumor imaging using molecular targeting with positron emission tomography and magnetic resonance imaging, as well as the role in patient management and possible therapeutic implications.

Assessment of the effect of therapy in a rat model of glioblastoma using [18F]FDG and [18F]FCho PET compared to contrast-enhanced MRI

Objective

We investigated the potential of [¹⁸F]fluorodeoxyglucose ([¹⁸F]FDG) and [¹⁸F]Fluoromethylcholine ([¹⁸F]FCho) PET, compared to contrast-enhanced MRI, for the early detection of treatment response in F98 glioblastoma (GB) rats.

Methods

When GB was confirmed on T2- and contrast-enhanced T1-weighted MRI, animals were randomized into a treatment group (n = 5) receiving MRI-guided 3D conformal arc micro-irradiation (20 Gy) with concomitant temozolomide, and a sham group (n = 5). Effect of treatment was evaluated by MRI and [¹⁸F]FDG PET on day 2, 5, 9 and 12 post-treatment and [¹⁸F]FCho PET on day 1, 6, 8 and 13 post-treatment. The metabolic tumor volume (MTV) was calculated using a semi-automatic thresholding method and the average tracer uptake within the MTV was converted to a standard uptake value (SUV).

Results

To detect treatment response, we found that for [¹⁸F]FDG PET (SUV_mean x MTV) is superior to MTV only. Using (SUV_mean x MTV), [¹⁸F]FDG PET detects treatment effect starting as soon as day 5 post-therapy, comparable to contrast-enhanced MRI. Importantly, [¹⁸F]FDG PET at delayed time intervals (240 min p.i.) was able to detect the treatment effect earlier, starting at day 2 post-irradiation. No significant differences were found at any time point for both the MTV and (SUV_mean x MTV) of [¹⁸F]FCho PET.

Conclusions

Both MRI and particularly delayed [¹⁸F]FDG PET were able to detect early treatment responses in GB rats, whereas, in this study this was not possible using [¹⁸F]FCho PET. Further comparative studies should corroborate these results and should also include (different) amino acid PET tracers.