[18F]FDG PET/CT-Avid Discordant Volume as a Biomarker in Patients with Gastroenteropancreatic Neuroendocrine Neoplasms: A Multicenter Study.

[18F]FDG PET/CT and [68Ga]Ga-DOTATATE PET/CT are both used to predict tumor biology in neuroendocrine neoplasms. Although the presence of discordant ([18F]FDG-avid/non-[68Ga]Ga-DOTATATE-avid) disease predicts poor prognosis, the significance of the volume of such discordant disease remains undetermined. The aim of this study is to investigate discordant tumor volume as a potential biomarker in patients with advanced gastroenteropancreatic neuroendocrine neoplasms (GEPNENs). Methods: A multicenter retrospective study in patients with advanced GEPNENs and paired [18F]FDG and [68Ga]Ga-DOTATATE PET/CT no more than 85 d apart was conducted. Patients with discordant disease were identified by the NETPET score, and discordant lesions were contoured with a flat [18F]FDG SUV cutoff of 4. The primary variable of interest was the total discordant volume (TDV), which was the sum of the volumes of discordant lesions. Patients were dichotomized into high- and low-TDV cohorts by the median value. The primary endpoint was overall survival. Results: In total, 44 patients were included (50% men; median age, 60 y), with primary cancers in the pancreas (45%), small bowel (23%), colon (20%), and other (12%). Of the patients, 5% had grade 1 disease, 48% had grade 2 disease, and 48% had grade 3 disease (24% well differentiated, 67% poorly differentiated, 10% unknown within the grade 3 cohort). The overall median survival was 14.1 mo. Overall survival was longer in the low-TDV cohort than in the high-TDV cohort (median volume, 43.7 cm3; survival time, 23.8 mo vs. 9.4 mo; hazard ratio, 0.466 [95% CI, 0.229-0.948]; P = 0.0221). Patients with no more than 2 discordant intrahepatic lesions survived longer than those with 2 or more lesions (31.8 mo vs. 10.2 mo, respectively; hazard ratio, 0.389 [95% CI, 0.194-0.779]; P = 0.0049). Conclusion: TDV is a potential prognostic biomarker in GEPNENs and should be investigated in future neuroendocrine neoplasm trials.

The predictive impact of dual somatostatin receptor/fluorodeoxyglucose (FDG) positron emission tomography (PET) in metastatic gastroenteropancreatic neuroendocrine tumors (GEP-NETs): review of literature and a single institution experience.

Treatment with radiolabelled somatostatin analogs, a form of peptide receptor radionuclide therapy (PRRT), has changed the management of patients with advanced gastroenteropancreatic neuroendocrine tumors (GEP-NETs). There is a subgroup of patients who have suboptimal benefit and rapidly progress on PRRT, indicating that accurate prognostic and predictive markers are urgently needed. Currently, most of the literature concentrate on the prognostic impact of the dual positron emission tomography (PET) scan with very few information regarding the predictive value. We report a case series and review the literature to summarizes the predictive value of combined somatostatin receptor (SSTR) and fluorodeoxyglucose (FDG) PET in metastatic GEP-NETs. We conducted a review of the literature for data published from 2010 to 2021 in MEDLINE, Embase, the National Institutes of Health trial registry, Cochrane CENTRAL, and published proceedings from major gastrointestinal and neuroendocrine cancer meetings. Our main criteria included all published prospective and retrospective data in which the predictive value of dual PET scans using SSTR and FDG was correlated with PRRT response in patients with metastatic GEP-NETs. We summarized clinical outcomes including progression-free survival (PFS), overall survival (OS), and post-therapy complications associated with PRRT according to FDG avidity. We excluded studies that did not include FDG PET scan, GEP patients, studies with no clear predictive value of the FDG PET scan, and studies that did not report a direct correlation between FDG avidity and primary outcome. Additionally, we summarized our institutional experience in eight patients who progressed during or within the first year of PRRT treatment. Our search identified 1306 articles; most of them showed only the prognostic value of Integrated SSTR/FDG PET imaging biomarker in GEP-NETs. Only three studies (n=75 patients) met our inclusion criteria and retrospectively investigated the predictive value of dual SSTR and FDG imaging in subjects being considered for PRRT. The results confirmed that FDG avidity correlates with advanced NET grades. Lesions that are both SSTR and FDG avid had early disease progression. In one study, at multivariate analysis, FDG PET results were independently predictive of lower PFS for PRRT. In our case series, there were eight patients with metastatic well-differentiated GEP-NETs (grades 2 and 3) who progressed within one year of PRRT. Seven of them had positive FDG PET scan at the time of progression. In conclusion, Dual SSTR/FDG PET imaging has a potential predictive impact for PRRT in GEP-NETs. It permits the capturing of the disease complexity and aggressiveness, which correlates with PRRT response. Therefore, prospective future trials should validate the predictive value of dual SSTRs/FDG PET for better PRRT stratification.

Synchronous Colorectal and Prostate Cancer: Dual PET/CT Approach for Detecting and Distinguishing Metastatic Patterns.

Prostate cancer (PC) and colorectal cancer (CRC) are two of the leading causes of cancer-related mortality. The incidence of synchronous neoplasms in patients with CRC is increasing, though synchronous PC and CRC remains a rare occurrence in clinical practice. Early diagnosis, accurate staging, and characterization of tumors are essential for selecting patient-tailored therapy. The origin of metastatic disease in synchronous cases presents a challenge for conventional imaging modalities, but advances in molecular imaging have addressed this limitation. Positron emission tomography/computed tomography (PET/CT) is now the preferred modality for assessing synchronous cases. The authors present a 72-year-old male patient with the rare occurrence of two coexisting primary cancers. At first, fluorine-18 fluorodeoxyglucose (18F-FDG) PET/CT detected the first colorectal primary tumor extension along with evidence of heterogeneous 18F-FDG activity within an enlarged prostate, warranting further evaluation. Subsequently, gallium-68 prostate-specific membrane antigen (68 Ga-PSMA) PET/CT imaging revealed the second prostate primary cancer with evidence of bone metastases. Adoption of a dual PET/CT approach in cases where biopsy is impractical can achieve accurate staging results during the initial diagnostic workup.

Gliosis and Neurodegenerative Diseases: The Role of PET and MR Imaging.

Glial activation characterizes most neurodegenerative and psychiatric diseases, often anticipating clinical manifestations and macroscopical brain alterations. Although imaging techniques have improved diagnostic accuracy in many neurological conditions, often supporting diagnosis, prognosis prediction and treatment outcome, very few molecular imaging probes, specifically focused on microglial and astrocytic activation, have been translated to a clinical setting. In this context, hybrid positron emission tomography (PET)/magnetic resonance (MR) scanners represent the most advanced tool for molecular imaging, combining the functional specificity of PET radiotracers (e.g., targeting metabolism, hypoxia, and inflammation) to both high-resolution and multiparametric information derived by MR in a single imaging acquisition session. This simultaneity of findings achievable by PET/MR, if useful for reciprocal technical adjustments regarding temporal and spatial cross-modal alignment/synchronization, opens still debated issues about its clinical value in neurological patients, possibly incompliant and highly variable from a clinical point of view. While several preclinical and clinical studies have investigated the sensitivity of PET tracers to track microglial (mainly TSPO ligands) and astrocytic (mainly MAOB ligands) activation, less studies have focused on MR specificity to this topic (e.g., through the assessment of diffusion properties and T2 relaxometry), and only few exploiting the integration of simultaneous hybrid acquisition. This review aims at summarizing and critically review the current state about PET and MR imaging for glial targets, as well as the potential added value of hybrid scanners for characterizing microglial and astrocytic activation.