Appropriate use of positron emission tomography with [(18)F]fluorodeoxyglucose for staging of oncology patients

Noninvasively Deciphering the Immunosuppressive Tumor Microenvironment Using Galectin-1 PET to Inform Immunotherapy Responses

Immune checkpoint blockade (ICB) has achieved groundbreaking results in clinical cancer therapy; however, only a subset of patients experience durable benefits. The aim of this study was to explore strategies for predicting tumor responses to optimize the intervention approach using ICB therapy. Methods: We used a bilateral mouse model for proteomics analysis to identify new imaging biomarkers for tumor responses to ICB therapy. A PET radiotracer was synthesized by radiolabeling the identified biomarker-targeting antibody with 124I. The radiotracer was then tested for PET prediction of tumor responses to ICB therapy. Results: We identified galectin-1 (Gal-1), a member of the carbohydrate-binding lectin family, as a potential negative biomarker for ICB efficacy. We established that Gal-1 inhibition promotes a sensitive immune phenotype within the tumor microenvironment (TME) for ICB therapy. To assess the pre-ICB treatment status of the TME, a Gal-1-targeted PET radiotracer, 124I-αGal-1, was developed. PET imaging with 124I-αGal-1 showed the pretreatment immunosuppressive status of the TME before the initiation of therapy, thus enabling the prediction of ICB resistance in advance. Moreover, the use of hydrogel scaffolds loaded with a Gal-1 inhibitor, thiodigalactoside, demonstrated that a single dose of thiodigalactoside-hydrogel significantly potentiated ICB and adoptive cell transfer immunotherapies by remodeling the immunosuppressive TME. Conclusion: Our study underscores the potential of Gal-1-targeted PET imaging as a valuable strategy for early-stage monitoring of tumor responses to ICB therapy. Additionally, Gal-1 inhibition effectively counteracts the immunosuppressive TME, resulting in enhanced immunotherapy efficacy.

Noninvasive interrogation of CD8+ T cell effector function for monitoring tumor early responses to immunotherapy

Accurately identifying patients who respond to immunotherapy remains clinically challenging. A noninvasive method that can longitudinally capture information about immune cell function and assist in the early assessment of tumor responses is highly desirable for precision immunotherapy. Here, we show that PET imaging using a granzyme B–targeted radiotracer named ⁶⁸Ga-grazytracer, could noninvasively and effectively predict tumor responses to immune checkpoint inhibitors and adoptive T cell transfer therapy in multiple tumor models. ⁶⁸Ga-grazytracer was designed and selected from several radiotracers based on non-aldehyde peptidomimetics, and exhibited excellent in vivo metabolic stability and favorable targeting efficiency to granzyme B secreted by effector CD8⁺ T cells during immune responses. ⁶⁸Ga-grazytracer permitted more sensitive discrimination of responders and nonresponders than did ¹⁸F-fluorodeoxyglucose, distinguishing between tumor pseudoprogression and true progression upon immune checkpoint blockade therapy in mouse models with varying immunogenicity. In a preliminary clinical trial with 5 patients, no adverse events were observed after ⁶⁸Ga-grazytracer injection, and clinical responses in cancer patients undergoing immunotherapy were favorably correlated with ⁶⁸Ga-grazytracer PET results. These results highlight the potential of ⁶⁸Ga-grazytracer PET to enhance the clinical effectiveness of granzyme B secretion–related immunotherapies by supporting early response assessment and precise patient stratification in a noninvasive and longitudinal manner.

Pineal gland hypermetabolic involvement without central nervous system symptoms in a pediatric patient with primary nodular sclerosis subtype classical Hodgkin Lymphoma

This case report presents the first reported pediatric case of primary classical nodular sclerosing Hodgkin Lymphoma (HL) with pineal gland involvement, presenting without CNS symptoms, which completely resolved after 2 cycles of chemotherapy. The 12 year-old male first presented with a right inguinal mass and external iliac lymphadenopathy accompanied by B symptoms. He was diagnosed with stage IV B classical HL, and as part of the staging work-up, a full-body PET/CT scan was performed. In addition to the right inguinal mass, the PET/CT demonstrated increased FDG uptake at the pineal gland along with level II lymph nodes. The patient was treated with ABVE-PC chemotherapy (Doxorubicin, Bleomycin, Vincristine, Etoposide, Prednisone, and Cyclophosphamide) as per standard arm of AHOD1331 COG protocol for newly diagnosed high-risk HL patients, which resolved the pineal mass after 2 cycles without requiring radiation therapy. Following 5 cycles, a full-body PET/CT showed no brain or neck activity, along with decreased size and activity of the right groin mass. To our knowledge, there are no other documented cases of primary HL with specific pineal involvement, and no cases that lack CNS symptoms altogether like this one did. Additionally, this is the third published pediatric case of primary CNS-HL, both of the previous cases were treated with radiotherapy and presented with CNS symptoms. Thus, this case demonstrates the importance of ordering a full-body PET/CT as part of the initial HL work-up and provides evidence that chemotherapy alone is a treatment option for some patients with primary intracranial HL.

The role of glycometabolic plasticity in cancer

Dysregulated glycometabolism represented by the Warburg effect is well recognized as a hallmark of cancer that can be driven by oncogenes (e.g., c-Myc, K-ras, and BRAF) and contribute to cellular malignant transformation. The Warburg effect reveals the different glycometabolic patterns of cancer cells, but this unique glycometabolic pattern has the characteristic of plasticity rather than changeless which can vary with different internal or external stimuli during evolution. Glycometabolic plasticity enables cancer cells to modulate glycometabolism to support progression, metastasis, treatment resistance and recurrence. In this review, we report the characteristics of glycometabolic plasticity during different stages of cancer evolution, providing insight into the molecular mechanisms of glycometabolic plasticity in cancer. In addition, we discussed the challenges and future research directions of glycometabolism research in cancer.

ICAM-1 orchestrates the abscopal effect of tumor radiotherapy

Compelling evidence indicates that radiotherapy (RT) has a systemic inhibitory effect on nonirradiated lesions (abscopal effect) in addition to the ablation of irradiated tumors. However, this effect occurs only in rare circumstances in clinical practice, and mechanisms underlying the abscopal effect of RT are neither fully understood nor therapeutically utilized. Here we identified that intercellular adhesion molecule-1 (ICAM-1), an inducible glycoprotein of the immunoglobulin superfamily, is up-regulated in nonirradiated tumors responsive to RT. ICAM-1 expression in preclinical animal models can be noninvasively detected by optical imaging and positron emission tomography (PET) using near-infrared fluorescence dye- and 64Cu-labeled imaging probes that we synthesized, respectively. Importantly, the expression levels of ICAM-1 determined by quantitative PET imaging showed a strong negative linear correlation with the growth of nonirradiated tumors. Moreover, genetic or pharmacologic up-regulation of ICAM-1 expression by either an intratumoral injection of engineered recombinant adenovirus or systemic administration of a Toll-like receptor 7 agonist-capsulated nanodrug could induce markedly increased abscopal responses to local RT in animal models. Mechanistic investigation revealed that ICAM-1 expression can enhance both the activation and tumor infiltration of CD8+ T cells to improve the responses of the nonirradiated tumors to RT. Together, our findings suggest that noninvasive PET imaging of ICAM-1 expression could be a powerful means to predict the responses of nonirradiated tumors to RT, which could facilitate the exploration of new combination RT strategies for effective ablation of primary and disseminated lesions.

Update on Quantitative Imaging for Predicting and Assessing Response in Oncology

Molecular imaging has revolutionized clinical oncology by imaging-specific facets of cancer biology. Through noninvasive measurements of tumor physiology, targeted radiotracers can serve as biomarkers for disease characterization, prognosis, response assessment, and predicting long-term response/survival. In turn, these imaging biomarkers can be utilized to tailor therapeutic regimens to tumor biology. In this article, we review biomarker applications for response assessment and predicting long-term outcomes. ¹⁸F-fluorodeoxyglucose (FDG), a measure of cellular glucose metabolism, is discussed in the context of lymphoma and breast and lung cancer. FDG has gained widespread clinical acceptance and has been integrated into the routine clinical care of several malignancies, most notably lymphoma. The novel radiotracers 16α-¹⁸F-fluoro-17β-estradiol and ¹⁸F-fluorothymidine are reviewed in application to the early prediction of response assessment of breast cancer. Through illustrative examples, we explore current and future applications of molecular imaging biomarkers in the advancement of precision medicine.

Clinical Translation of a 68Ga-Labeled Integrin αvβ6-Targeting Cyclic Radiotracer for PET Imaging of Pancreatic Cancer

The overexpression of integrin α_vβ₆ in pancreatic cancer makes it a promising target for noninvasive PET imaging. However, currently, most integrin α_vβ₆-targeting radiotracers are based on linear peptides, which are quickly degraded in the serum by proteinases. Herein, we aimed to develop and assess a ⁶⁸Ga-labeled integrin α_vβ₆-targeting cyclic peptide (⁶⁸Ga-cycratide) for PET imaging of pancreatic cancer. Methods: ⁶⁸Ga-cycratide was prepared, and its PET imaging profile was compared with that of the linear peptide (⁶⁸Ga-linear-pep) in an integrin α_vβ₆-positive BxPC-3 human pancreatic cancer mouse model. Five healthy volunteers (2 women and 3 men) underwent whole-body PET/CT imaging after injection of ⁶⁸Ga-cycratide, and biodistribution and dosimetry were calculated. PET/CT imaging of 2 patients was performed to investigate the potential role of ⁶⁸Ga-cycratide in pancreatic cancer diagnosis and treatment monitoring. Results: ⁶⁸Ga-cycratide exhibited significantly higher tumor uptake than did ⁶⁸Ga-linear-pep in BxPC-3 tumor-bearing mice, owing-at least in part-to markedly improved in vivo stability. ⁶⁸Ga-cycratide could sensitively detect the pancreatic cancer lesions in an orthotopic mouse model and was well tolerated in all healthy volunteers. Preliminary PET/CT imaging in patients with pancreatic cancer demonstrated that ⁶⁸Ga-cycratide was comparable to ¹⁸F-FDG for diagnostic imaging and postsurgery tumor relapse monitoring. Conclusion: ⁶⁸Ga-cycratide is an integrin α_vβ₆-specific PET radiotracer with favorable pharmacokinetics and a favorable dosimetry profile. ⁶⁸Ga-cycratide is expected to provide an effective noninvasive PET strategy for pancreatic cancer lesion detection and therapy response monitoring.

Malignant Cutaneous Melanoma: Updates in PET Imaging

BACKGROUND

Cutaneous malignant melanoma is a neoplasm whose incidence and mortality are dramatically increasing. 18F-FDG PET/CT gained clinical acceptance over the past 2 decades in the evaluation of several glucose-avid neoplasms, including malignant melanoma, particularly for the assessment for distant metastases, recurrence and response to therapy.

OBJECTIVE

To describe the advancements of nuclear medicine for imaging melanoma with particular attention to 18F-FDG-PET and its current state-of-the-art technical innovations.

METHODS

A comprehensive search strategy was used based on SCOPUS and PubMed databases. From all studies published in English, we selected the articles that evaluated the technological insights of 18FFDG- PET in the assessment of melanoma.

RESULTS

State-of-the-art silicon photomultipliers based detectors ("digital") PET/CT scanners are nowadays more common, showing technical innovations that may have beneficial implications for patients with melanoma. Steady improvements in detectors design and architecture, as well as the implementation of both software and hardware technology (i.e., TOF, point spread function, etc.), resulted in significant improvements in PET image quality while reducing radiotracer dose and scanning time.

CONCLUSION

Recently introduced digital PET detector technology in PET/CT and PET/MRI yields higher intrinsic system sensitivity compared with the latest generation analog technology, enabling the detection of very small lesions with potential impact on disease outcome.

68Ga-FAPI PET/CT: Tracer Uptake in 28 Different Kinds of Cancer

The recent development of quinoline-based PET tracers that act as fibroblast-activation-protein inhibitors (FAPIs) demonstrated promising preclinical and clinical results. FAP is overexpressed by cancer-associated fibroblasts of several tumor entities. Here, we quantify the tumor uptake on ⁶⁸Ga-FAPI PET/CT of various primary and metastatic tumors to identify the most promising indications for future application. Methods: ⁶⁸Ga-FAPI PET/CT scans were requested by various referring physicians according to individual clinical indications that were considered insufficiently covered by ¹⁸F-FDG PET/CT or other imaging modalities. All PET/CT was performed 1 h after injection of 122-312 MBq of ⁶⁸Ga-FAPI-04. We retrospectively identified 80 patients with histopathologically proven primary tumors or metastases or radiologically unequivocal metastatic lesions of histologically proven primary tumors. Tumor uptake was quantified by SUV_max and SUV_mean (60% isocontour). Results: Eighty patients with 28 different tumor entities (54 primary tumors and 229 metastases) were evaluated. The highest average SUV_max (>12) was found in sarcoma, esophageal, breast, cholangiocarcinoma, and lung cancer. The lowest ⁶⁸Ga-FAPI uptake (average SUV_max < 6) was observed in pheochromocytoma, renal cell, differentiated thyroid, adenoid cystic, and gastric cancer. The average SUV_max of hepatocellular, colorectal, head-neck, ovarian, pancreatic, and prostate cancer was intermediate (SUV 6-12). SUV varied across and within all tumor entities. Because of low background in muscle and blood pool (SUV_max < 2), the tumor-to-background contrast ratios were more than 3-fold in the intermediate and more than 6-fold in the high-intensity uptake group. Conclusion: Several highly prevalent cancers presented with remarkably high uptake and image contrast on ⁶⁸Ga-FAPI PET/CT. The high and rather selective tumor uptake may open up new applications for noninvasive tumor characterization, staging examinations, or radioligand therapy.

Preclinical Development and First-in-Human Imaging of the Integrin αvβ6 with [18F]αvβ6-Binding Peptide in Metastatic Carcinoma

PURPOSE

The study was undertaken to develop and evaluate the potential of an integrin αvβ6-binding peptide (αvβ6-BP) for noninvasive imaging of a diverse range of malignancies with PET.

EXPERIMENTAL DESIGN

The peptide αvβ6-BP was prepared on solid phase and radiolabeled with 4-[18F]fluorobenzoic acid. In vitro testing included ELISA, serum stability, and cell binding studies using paired αvβ6-expressing and αvβ6-null cell lines. In vivo evaluation (PET/CT, biodistribution, and autoradiography) was performed in a mouse model bearing the same paired αvβ6-expressing and αvβ6-null cell xenografts. A first-in-human PET/CT imaging study was performed in patients with metastatic lung, colon, breast, or pancreatic cancer.

RESULTS

[18F]αvβ6-BP displayed excellent affinity and selectivity for the integrin αvβ6 in vitro [IC50(αvβ6) = 1.2 nmol/L vs IC50(αvβ3) >10 μmol/L] in addition to rapid target-specific cell binding and internalization (72.5% ± 0.9% binding and 52.5% ± 1.8%, respectively). Favorable tumor affinity and selectivity were retained in the mouse model and excretion of unbound [18F]αvβ6-BP was rapid, primarily via the kidneys. In patients, [18F]αvβ6-BP was well tolerated without noticeable adverse side effects. PET images showed significant uptake of [18F]αvβ6-BP in both the primary lesion and metastases, including metastasis to brain, bone, liver, and lung.

CONCLUSIONS

The clinical impact of [18F]αvβ6-BP PET imaging demonstrated in this first-in-human study is immediate for a broad spectrum of malignancies.

Automated radiosynthesis of 5-[11C]l-glutamine, an important tracer for glutamine utilization

INTRODUCTION

The natural amino acid l-Glutamine (Gln) is essential for both cell growth and proliferation. In addition to glucose, cancer cells utilize Gln as a carbon source for ATP production, biosynthesis, and as a defense against reactive oxygen species. The utilization of [¹¹C]Gln has been previously reported as a biomarker for tissues with an elevated demand for Gln, however, the previous reports for the preparation of [¹¹C]Gln were found to be lacking several crucial aspects necessary for transition to human production. Namely, the presence of unreacted precursor and the use of non-commercialized, custom built, reaction platforms. Herein, we report the development and utilization of methodology for the automated production of [¹¹C]Gln that meets institutional criteria for human use.

METHODS

The preparation of [¹¹C]Gln was carried out on the GE FX₂N platform. Briefly, after trapping of [¹¹C]HCN with a solution of CsHCO₃ in DMF, the [¹¹C]CsCN was reacted with a commercially available precursor. This intermediate was then purified by HPLC and deprotected/hydrolyzed under acidic conditions. Following pH adjustment, the product was filtered to give the desired [¹¹C]Gln as a sterile injectable. The resulting product was then analyzed for quality assurance.

RESULTS

Automated production by this method reliably provides over 3.7 GBq (100 mCi) of [¹¹C]Gln. The resulting final drug product was found to have a >99% radiochemical purity, <5% of D-Gln present, no detectable impurities, and the total preparation time was roughly 45 min from the end-of-bombardment.

CONCLUSIONS

A fast, reliable and efficient automated radiosynthesis was developed using a commercially available module. Purifications used throughout allow for both a radiochemically and chemically pure final product solution of [¹¹C]Gln.

Non-Invasive Glutamine PET Reflects Pharmacological Inhibition of BRAFV600E In Vivo

PURPOSE

This study aimed to study whether cancer cells possess distinguishing metabolic features compared with surrounding normal cells, such as increased glutamine uptake. Given this, quantitative measures of glutamine uptake may reflect critical processes in oncology. Approximately, 10 % of patients with colorectal cancer (CRC) express BRAF ^V600E , which may be actionable with selective BRAF inhibitors or in combination with inhibitors of complementary signaling axes. Non-invasive and quantitative predictive measures of response to these targeted therapies remain poorly developed in this setting. The primary objective of this study was to explore 4-[¹⁸F]fluoroglutamine (4-[¹⁸F]F-GLN) positron emission tomography (PET) to predict response to BRAF^V600E-targeted therapy in preclinical models of colon cancer.

PROCEDURES

Tumor microarrays from patients with primary human colon cancers (n = 115) and CRC liver metastases (n = 111) were used to evaluate the prevalence of ASCT2, the primary glutamine transporter in oncology, by immunohistochemistry. Subsequently, 4-[¹⁸F]F-GLN PET was evaluated in mouse models of human BRAF ^V600E -expressing and BRAF wild-type CRC.

RESULTS

Approximately 70 % of primary colon cancers and 53 % of metastases exhibited positive ASCT2 immunoreactivity, suggesting that [¹⁸F]4-F-GLN PET could be applicable to a majority of patients with colon cancer. ASCT2 expression was not associated selectively with the expression of mutant BRAF. Decreased 4-[¹⁸F]F-GLN predicted pharmacological response to single-agent BRAF and combination BRAF and PI3K/mTOR inhibition in BRAF ^V600E -mutant Colo-205 tumors. In contrast, a similar decrease was not observed in BRAF wild-type HCT-116 tumors, a setting where BRAF^V600E-targeted therapies are ineffective.

CONCLUSIONS

4-[¹⁸F]F-GLN PET selectively reflected pharmacodynamic response to BRAF inhibition when compared with 2-deoxy-2[¹⁸F]fluoro-D-glucose PET, which was decreased non-specifically for all treated cohorts, regardless of downstream pathway inhibition. These findings illustrate the utility of non-invasive PET imaging measures of glutamine uptake to selectively predict response to BRAF-targeted therapy in colon cancer and may suggest further opportunities to inform colon cancer clinical trials using targeted therapies against MAPK activation.

Investigation of Association Between Borderline Pancreatic Head Cancer and Glucose Uptake by Using Positron-Emission Tomographic Studies

BACKGROUND In the background of the well-known importance of positron-emission tomographic studies (PET) in the prediction of pancreatic oncologic problems, we designed and performed this investigation to study the link between borderline pancreatic head cancer and glucose uptake by using PET. MATERIAL AND METHODS We retrospectively investigated patients during the period of almost 4 years (May 2013 to December 2016). Patients underwent potentially curative resection for borderline exocrine pancreatic head adenocarcinoma without undergoing neoadjuvant therapy. We divided our PET protocol into 2 sets of methods as per renal calyces: 1) U-RC type in which renal calyx (RC) has relatively higher value than that of 18F-fluoro-2-deoxyglucose (18F-FDG) uptake and 2) S-RC type in which renal calyx has similar value than that of 18F-FDG uptake. RESULTS A total of 67 patients were enrolled after reclassification on the basis of majority-agreement. Among these patients, U-RC type was found in 22 patients (32.8%) while S-RC type was found in 45 patients (67.2%). Significant statistical differences were observed for each of the 2 types of pancreatic head cancer (U-RC type and S-RC type) in terms of adjusted cancer antigen 19-9 (CA 19-9), size of the tumor, tumor volume (TV2.8), maximum standard uptake value (SUV↑), and lesion glycolysis (LG). A significantly longer disease-free survival time was shown by U-RC type (n=18) pancreatic cancer in comparison to S-RC type (n=42) (25.3 vs. 11.2 months). Additionally, U-RC type (n=4) had higher disease-free survival than did aS-RC type (n=3) (29.4 vs. 12.5 months). CONCLUSIONS Our PET protocol appears to be an indicator for estimation of recurrence of pancreatic head cancer and is as an indispensable asset to oncologists.

Development of a radiolabeled caninized anti-EGFR antibody for comparative oncology trials

Due to large homology of human and canine EGFR, dogs suffering from spontaneous EGFR+ cancer can be considered as ideal translational models. Thereby, novel immunotherapeutic compounds can be developed for both human and veterinary patients. This study describes the radiolabeling of a canine anti-EGFR IgG antibody (can225IgG) with potential diagnostic and therapeutic value in comparative clinical settings. Can225IgG was functionalized with DTPA for subsequent chelation with the radionuclide ^99mTc. Successful coupling of 10 DTPA molecules per antibody on average was proven by significant mass increase in MALDI-TOF spectroscopy, gel electrophoresis and immunoblots. Following functionalization and radiolabeling, ^99mTc-DTPA-can225IgG fully retained its binding capacity towards human and canine EGFR in flow cytometry, immuno- and radioblots, and autoradiography. The affinity of radiolabeled can225IgG was determined to K_D 0.8 ±0.0031 nM in a real-time kinetics assay on canine carcinoma cells by a competition binding technique. Stability tests of the radiolabeled compound identified TRIS buffered saline as the ideal formulation for short-term storage with 87.11 ±6.04% intact compound being still detected 60 minutes post radiolabeling. High stability, specificity and EGFR binding affinity pinpoint towards ^99mTc-radiolabeled can225IgG antibody as an ideal lead compound for the first proof-of-concept diagnostic and therapeutic applications in canine cancer patients.

Image improvement method for positron emission mammography

PURPOSE

To evaluate in clinical use a rapidly converging, efficient iterative deconvolution algorithm (RSEMD) for improving the quantitative accuracy of previously reconstructed breast images by a commercial positron emission mammography (PEM) scanner.

MATERIALS AND METHODS

The RSEMD method was tested on imaging data from clinical Naviscan Flex Solo II PEM scanner. This method was applied to anthropomorphic like breast phantom data and patient breast images previously reconstructed with Naviscan software to determine improvements in image resolution, signal to noise ratio (SNR) and contrast to noise ratio (CNR).

RESULTS

In all of the patients' breast studies the improved images proved to have higher resolution, contrast and lower noise as compared with images reconstructed by conventional methods. In general, the values of CNR reached a plateau at an average of 6 iterations with an average improvement factor of about 2 for post-reconstructed Flex Solo II PEM images. Improvements in image resolution after the application of RSEMD have also been demonstrated.

CONCLUSIONS

A rapidly converging, iterative deconvolution algorithm with a resolution subsets-based approach (RSEMD) that operates on patient DICOM images has been used for quantitative improvement in breast imaging. The RSEMD method can be applied to PEM images to enhance the resolution and contrast in cancer diagnosis to monitor the tumor progression at the earliest stages.

Evaluation and optimization of occupational eye lens dosimetry during positron emission tomography (PET) procedures

The last recommendations of the International Commission on Radiological Protection for eye lens dose suggest an important reduction on the radiation limits associated with early and late tissue reactions. The aim of this work is to quantify and optimize the eye lens dose associated to nurse staff during positron emission tomography (PET) procedures. PET is one of the most important diagnostic methods of oncological and neurological cancer disease involving an important number of workers exposed to the high energy isotope F-18. We characterize the relevant stages as preparation and administration of monodose syringes in terms of occupational dose. A direct reading silicon dosimeter was used to measure the lens dose to staff. The highest dose of radiation was observed during preparation of the fluorodesoxyglucose (FDG) syringes. By optimizing a suitable vials' distribution of FDG we find an important reduction in occupational doses. Extrapolation of our data to other clinical scenarios indicates that, depending on the work load and/or syringes activity, safety limits of the dose might be exceeded.

Variability of [18F]FDG administered activities among patients undergoing PET examinations: an international multicenter survey

Given the large number of [(18)F]fluorodeoxyglucose (FDG) PET examinations performed annually throughout the world, reduction of the administered activity without compromise of the clinical information being sought is encouraged. Guidelines issued by the SNMMI and European Association of Nuclear Medicine (EANM) differ greatly on the choice of the activity that should be administered to patients: the EANM suggests a personalised activity based on the patient's body weight, whereas the SNMMI recommends the administration of fixed activities. The authors analysed a database of 24 716 [(18)F]FDG administrations performed worldwide in 15 PET centres to assess the degree of heterogeneity, in relation to available technology, operational protocols and reference guidelines. Median activities based on the patients' body weight were 43 % lower than fixed-activity administrations (p < 0.001). When TOF scanners are available, the median activity is lowered, but when comparing centres with the same technology or those that use the same operational protocols, weight-based activities are still significantly lower than fixed activities.

Clinicopathologic Features and Molecular Characteristics of Glucose Metabolism Contributing to ¹⁸F-fluorodeoxyglucose Uptake in Gastrointestinal Stromal Tumors

Fluorine-18 fluorodeoxyglucose (18F-FDG) positron emission tomography-computed tomography (PET/CT) is useful in the preoperative diagnosis of gastrointestinal stromal tumors (GISTs); however, the molecular characteristics of glucose metabolism of GIST are unknown. We evaluated 18F-FDG uptake on preoperative PET/CT of 40 patients and analyzed the expression of glycolytic enzymes in resected GIST tissues by qRT-PCR, western blotting, and immunohistochemistry. Results of receiver operating characteristic curve analysis showed that the maximum standardized uptake value (SUVmax) cut-off value of 4.99 had a sensitivity of 89.5%, specificity was 76.2%, and accuracy of 82.5% for identifying tumors with a high risk of malignancy. We found that 18F-FDG uptake correlated positively with tumor size, risk grade, and expression levels of glucose transporter 1 (GLUT1), hexokinase 1 (HK1), and lactate dehydrogenase A (LDHA). Elevated HK and LDH activity was found in high-risk tumors. Among the isoforms of GLUT and HK, GLUT1 and HK1 expression increased with higher tumor risk grade. In addition, overexpression of glycolytic enzymes M2 isoform of pyruvate kinase (PKM2) and LDHA was observed in GISTs, especially in high-risk tumors. These results suggest that upregulation of GLUT1, HK1, PKM2, and LDHA may play an important role in GIST tumorigenesis and may be useful in the preoperative prediction of malignant potential.

(18)F-FDG PET/CT and Melanoma: Staging, Immune Modulation and Mutation-Targeted Therapy Assessment, and Prognosis

OBJECTIVE

Monoclonal antibodies that target the programmed cell death 1 (PD-1) immune checkpoint protein and its associated ligands, PD-L1 and PD-L2, and targeted inhibitors of mutated signal transduction molecules such as BRAF inhibitors show immense promise in treating patients with melanoma. We discuss the use of (18)F-FDG PET/CT for assessing therapy effectiveness, staging advanced disease, and determining prognosis of patients with melanoma.

CONCLUSION

FDG PET/CT is useful in staging disease, assessing therapy, and determining prognosis in patients with melanoma.

Evolving role of positron emission tomography (PET) in urological malignancy

We present a review on the increasing indications for the use of positron emission tomography (PET) in uro-oncology. In this review we describe the details of the different types of PET scans, indications for requesting PET scans in specific urological malignancy and the interpretation of the results.

Additional information gained by positron emission tomography with (68)Ga-DOTATOC for suspected unknown primary or recurrent neuroendocrine tumors

Objective

Positron emission tomography (PET)/computed tomography (CT) using ⁶⁸Ga-labeled 1,4,7,10-tetraazacyclododecane-N,N′,N″,N‴-tetraacetic acid-d-Phe¹-Tyr³-octreotide (DOTATOC) has been used to detect neuroendocrine tumors (NETs). The purpose of this study was to investigate the clinical efficacy of DOTATOC-PET/CT for detecting clinically suspected NETs when conventional imaging modalities were negative or inconclusive, in terms of additional value.

Methods

A total of 46 patients were analyzed retrospectively. Among them, 14 patients underwent a DOTATOC-PET/CT scan for detecting unknown primary tumors after histopathological confirmation of a NET at metastatic sites (group A): 7 patients for detecting metastasis or recurrence after surgery for NET because of their high hormone levels but with no recurrence detected by other imaging modalities (group B); the remaining 25 patients for detecting suspected NETs because their hormone levels were high with no history of histopathologically proven NET (group C). Additional information was assessed, according to each situation.

Results

In group A, unknown primary tumors were suspected by DOTATOC-PET/CT in 8 of 14 patients (gastrointestinal/pancreatic NET in 7 patients, prostatic cancer in 1 patient), but prostatic cancer was not confirmed by histopathology (i.e., false positive). In group B, DOTATOC-PET/CT depicted lesions in six of seven patients, including nodal metastasis (n = 5) and liver metastasis (n = 1). In group C, DOTATOC-PET/CT did not demonstrate any abnormal foci except in one case of pancreatic NET. Additional information was obtained in 50, 86, and 4 % of cases, in groups A, B, and C, respectively.

Conclusions

DOTATOC-PET/CT was useful for detecting NETs, especially when recurrence or metastases were suspected because of high hormone levels after surgery for a NET. It is unlikely, however, that additional information can be acquired in patients with no history of NET simply based on high hormone levels.