68Ga-PSMA is a novel PET-CT tracer for imaging of hepatocellular carcinoma: A prospective pilot study

PSMA radioligand therapy for solid tumors other than prostate cancer: background, opportunities, challenges, and first clinical reports

In the past decade, a growing body of literature has reported promising results for prostate-specific membrane antigen (PSMA)-targeted radionuclide imaging and therapy in prostate cancer. First clinical studies evaluating the efficacy of [¹⁷⁷Lu]Lu-PSMA radioligand therapy (PSMA-RLT) demonstrated favorable results in prostate cancer patients. [¹⁷⁷Lu]Lu-PSMA is generally well tolerated due to its limited side effects. While PSMA is highly overexpressed in prostate cancer cells, varying degrees of PSMA expression have been reported in other malignancies as well, particularly in the tumor-associated neovasculature. Hence, it is anticipated that PSMA-RLT could be explored for other solid cancers. Here, we describe the current knowledge of PSMA expression in other solid cancers and define a perspective towards broader clinical implementation of PSMA-RLT. This review focuses specifically on salivary gland cancer, glioblastoma, thyroid cancer, renal cell carcinoma, hepatocellular carcinoma, lung cancer, and breast cancer. An overview of the (pre)clinical data on PSMA immunohistochemistry and PSMA PET/CT imaging is provided and summarized. Furthermore, the first clinical reports of non-prostate cancer patients treated with PSMA-RLT are described.

68Ga-PSMA PET/CT Versus 18F-FDG PET/CT for Imaging of Hepatocellular Carcinoma

Objectives:

This study aimed to compare the metabolic parameters obtained from ¹⁸fluorine-fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography/computed tomography (PET/CT) and gallium-68 (⁶⁸Ga)-prostate-specific membrane antigen (PSMA) PET/CT and investigate the relationship between serum alpha-fetoprotein and PET scan parameters in patients with hepatocellular carcinoma.

Methods:

Fourteen patients were recruited after dynamic magnetic resonance imaging (MRI) of the upper abdomen, and ¹⁸F-FDG and ⁶⁸Ga-PSMA PET/CT imaging studies were conducted. Regions of interest (ROIs) were drawn from lesion-free liver tissue, abdominal aorta (A), and right medial gluteal muscle (G) for the background activity. Maximum standard uptake value (SUV_max) of these regions were compared with the SUV_max of primary tumor (T).

Results:

On visual assessment, five patients (36%) experienced low ¹⁸F-FDG uptake in the primary lesion, three patients (21%) experienced moderate uptake, and six patients (43%) experienced high uptake. However, only one patient (7%) showed low ⁶⁸Ga-PSMA uptake, two patients (14%) showed moderate uptake, and 11 patients (79%) showed high uptake. Four patients with a low ¹⁸F-FDG uptake showed high ⁶⁸Ga-PSMA uptake, while one patient exhibited low uptake with both ¹⁸F-FDG and ⁶⁸Ga-PSMA. The number of lesions on ⁶⁸Ga-PSMA PET/CT and MRI was significantly higher than ¹⁸F-FDG PET/CT (p=0.042 and 0.026, respectively). T/A and T/G values were significantly higher in ⁶⁸Ga-PSMA than ¹⁸F-FDG (p=0.002 and 0.002, respectively).

Conclusion:

⁶⁸Ga-PSMA PET/CT is superior to ¹⁸F-FDG PET/CT in the staging of hepatocellular carcinoma. High ⁶⁸Ga-PSMA uptake could be promising for PSMA-targeted radionuclide treatments.

PET/CT Variants and Pitfalls in Liver, Biliary Tract, Gallbladder and Pancreas

A wide variety of pathological anomalies may occur in the liver, biliary system, and pancreas. It is a necessity to use many different imaging techniques in order to distinguish such varied pathologies, especially those from malignant processes. Positron Emission Tomography/Computed Tomography (PET/CT) is an imaging method that has proven its diagnostic value in oncology and can be used for different clinical purposes. Fluoro-18 fluoro-2-deoxy-D-glucose has a wide range of uses as a dominant radiopharmaceutical in routine molecular imaging, however, molecular imaging has started to play a more important role in personalized cancer treatment in recent years with new Fluoro-18 and Gallium-68 labeled tracers. Although molecular imaging has a strong diagnostic effect, the surprises and pitfalls of molecular imaging can lead us to unexpected and misleading results. Prior to PET/CT analysis and reporting, information about possible technical and physiological pitfalls, normal histological features of tissues, inflammatory pathologies, specific clinical features of the case, treatment-related complications and past treatments should be evaluated in advance to avoid misinterpretation. In this review, the physiological and pathophysiological variants as well as pitfalls encountered in PET/CT imaging of the liver, biliary tract, gallbladder, and pancreas will be examined. Other benign and malignant pathologies that have been reported to date and that have led to incorrect evaluation will be listed. It is expected that the devices, software, and artificial intelligence applications that will be developed in the near future will enable much more effective and faster imaging that will reduce the potential causes of error. However, as a result of the dynamic and evolving structure of the information obtained by molecular imaging, the inclusion of the newly developed radiopharmaceuticals in routine practice will continue to carry new potentials as well as new troubles. Although molecular imaging will be the flagship of diagnostic oncology in the 21st century, the correct analysis and interpretation by the physician will continue to form the basis of achieving optimal performance.

Automatic radiosynthesis and preclinical evaluation of 18F-AlF-PSMA-NF as a potential PET probe for prostate cancer imaging

Facile automatic production is important for the application of prostate-specific membrane antigen (PSMA) tracers in clinical practice. We developed a new ¹⁸F-AlF-labelled PSMA probe-¹⁸F-AlF-PSMA-NF-and explore its automated production method and potential value in clinical settings. ¹⁸F-AlF-PSMA-NF was prepared using an automated method with dimethylformamide (DMF) as the solvent in a positron emission tomography (PET)-MF-2 V-IT-I synthesizer. Tracer characteristics were examined both in vitro and in vivo. Micro-PET/computed tomography (CT) was performed to investigate the utility of ¹⁸F-AlF-PSMA-NF for imaging PSMA-positive tumours in vivo. ¹⁸F-AlF-PSMA-NF was prepared automatically within 35 min with a non-attenuation correction yield of 37.9 ± 11.2%. The tracer was hydrophilic, had a high affinity for PSMA (Kd = 2.58 ± 0.81 nM), and showed stability in both in vitro and in vivo conditions. In the cellular experiments, ¹⁸F-AlF-PSMA-NF uptake in PSMA-positive LNCaP cells was significantly higher than that in PSMA-negative PC-3 cells (P < 0.001), and could be blocked by excess ZJ-43-a PSMA inhibitor (P < 0.001). LNCaP tumours were clearly visualized by ¹⁸F-AlF-PSMA-NF on micro-PET/CT, with a high level of uptake (13.72 ± 2.01 percent injected dose per gram of tissue [%ID/g]) and high tumour/muscle ratio (close to 50:1). The PSMA-positive LNCaP tumours had a significantly higher uptake than PSMA-negative PC-3 tumours (13.72 ± 2.01%ID/g vs. 1.07 ± 0.48%ID/g, t = 10.382, P < 0.001), and could be blocked by ZJ-43 (13.72 ± 2.01%ID/g vs. 2.77 ± 1.44%ID/g, t = 8.14, P < 0.001). A new ¹⁸F-AlF-labelled PSMA probe-¹⁸F-AlF-PSMA-NF-was successfully developed and can be prepared automatically. It has the biological characteristics resembling that of a PSMA-based probe and can potentially be used in clinical settings.

E-PSMA: the EANM standardized reporting guidelines v1.0 for PSMA-PET

RATIONALE

The development of consensus guidelines for interpretation of Prostate-Specific Membrane Antigen (PSMA)-Positron Emission Tomography (PET) is needed to provide more consistent reports in clinical practice. The standardization of PSMA-PET interpretation may also contribute to increasing the data reproducibility within clinical trials. Finally, guidelines in PSMA-PET interpretation are needed to communicate the exact location of findings to referring physicians, to support clinician therapeutic management decisions.

METHODS

A panel of worldwide experts in PSMA-PET was established. Panelists were selected based on their expertise and publication record in the diagnosis or treatment of PCa, in their involvement in clinical guidelines and according to their expertise in the clinical application of radiolabeled PSMA inhibitors. Panelists were actively involved in all stages of a modified, nonanonymous, Delphi consensus process.

RESULTS

According to the findings obtained by modified Delphi consensus process, panelist recommendations were implemented in a structured report for PSMA-PET.

CONCLUSIONS

The E-PSMA standardized reporting guidelines, a document supported by the European Association of Nuclear Medicine (EANM), provide consensus statements among a panel of experts in PSMA-PET imaging, to develop a structured report for PSMA-PET in prostate cancer and to harmonize diagnostic interpretation criteria.

Prostate-specific Membrane Antigen PET in Prostate Cancer

Prostate-specific membrane antigen (PSMA)-targeted radiopharmaceuticals are playing a large role at the time of initial staging and biochemical recurrence for localizing prostate cancer, as well as in other emerging clinical settings. PSMA PET has demonstrated increased detection rate compared with conventional imaging and has been shown to change management plans in a substantial percentage of cases. The aims of this narrative review are to highlight the development and clinical impact of PSMA PET radiopharmaceuticals, to compare PSMA to other agents such as fluorine 18 fluciclovine and carbon 11 choline, and to highlight some of the individual PSMA PET agents that have contributed to the advancement of prostate cancer imaging.

68Ga-Prostate-Specific Membrane Antigen Uptake as a Surrogate Biomarker of Neovascularity in Hepatocellular Carcinoma

⁶⁸Ga-prostate-specific membrane antigen (⁶⁸Ga-PSMA) is expressed in the endothelium of tumor-associated neovasculature of various solid malignancies possibly due to tumor-associated angiogenic factors and endothelial cell sprouting. We report a case of a 45-year-old man with known colorectal cancer, cirrhosis, and hepatitis C. Contrast-enhanced computed tomography (CT) showed a hypervascular lesion in the liver, and ¹⁸F-fluorodeoxyglucose positron emission tomography (PET) did not show any suspicious hepatic uptake. ⁶⁸Ga-PSMA PET-CT showed predominantly heterogeneous perilesional uptake in a configuration similar to the arterial enhancement pattern on the diagnostic CT. ⁶⁸Ga-PSMA uptake in hepatocellular carcinoma appears to be primarily neoangiogenesis driven, and its morphological and functional characterization can subsequently influence the selection of anti-neoangiogenic chemotherapy agents as well as guiding radionuclide ligand therapy.

Incidental Finding of a PSMA-Positive Pancreatic Cancer in a Patient Suffering from a Metastasized PSMA-Positive Prostate Cancer

An 82-year-old man suffering from prostate cancer that was scheduled for a radioreceptor-ligand therapy (RLT) presented with jaundice to our service. An abdominal ultrasound (US) revealed obstructive extrahepatic cholestasis due to a solid lesion located in the uncinate process of the pancreas. The Prostate Specific Membrane Antigen (PSMA) PET/CT prior to RLT showed multilocular PSMA positive tumor lesions in the lymph nodes, the lung and the pancreas. On request of the cancer board, an Endoscopic Ultrasound (EUS)-guided Fine-Needle Aspiration (FNA) of the pancreatic mass was performed revealing invasive pancreatic ductal adenocarcinoma incompatible with a prostate cancer metastasis leading to the diagnosis of a PSMA positive pancreatic ductal adenocarcinoma.

Prostate-specific membrane antigen expression in hepatocellular carcinoma, cholangiocarcinoma, and liver cirrhosis

BACKGROUND

Primary liver cancer includes three subtypes: Hepatocellular carcinoma (HCC), intrahepatic cholangiocarcinoma (CCA), and combined hepatocellular carcinoma. Patients with primary liver cancer experienced poor prognosis and high mortality, so early detection of liver cancer and improved management of metastases are both key strategies to reduce the death toll from liver cancer. Prostate-specific membrane antigen (PSMA) expression in the tumor-associated neovasculature of nonprostate malignancies including liver cancer has been reported recently, but conclusive evidence of PSMA expression based on the pathological type of liver cancer remains limited.

AIM

To study the expression of PSMA in HCC, CCA, and liver cirrhosis.

METHODS

A total of 446 formalin-fixed paraffin-embedded (FFPE) liver tumor and liver cirrhosis tissue samples were obtained retrospectively from the Pathology Department of Tongji Hospital. Immunohistochemistry was used to detect PSMA expression in these 446 FFPE liver biopsy specimens (213 HCC, 203 CCA, and 30 liver cirrhosis). The tumor compartment and the associated neovascular endothelium were separately analyzed. PSMA expression was examined by two certified pathologists, and the final results were presented in a 4-point scoring system (0-3 points). Correlation between PSMA expression and clinicopathological information was also assessed.

RESULTS

PSMA was expressed primarily in the neovascular endothelium associated with tumors. The positive rate of PSMA staining in HCC was significantly higher than that in CCA (86.8% vs 79.3%; P = 0.001) but was only 6.6% in liver cirrhosis (P = 0.000). HCC cases had more 3-score PSMA staining than CCA had (89/213, 41.8% vs 35/203, 17.2%; P = 0.001). PSMA expression correlated positively with the stage and grade of HCC and CCA. In both liver cancer subtypes, there were more PSMA⁺ cases in stages III–V diseases than in stages I and II. High staining intensity of PSMA was more frequently observed in liver cancers at high grade and advanced stage. There was no significant association of PSMA expression with sex, age, region, α-fetoprotein, hepatitis B surface antigen, or tumor size in both tumor subtypes.

CONCLUSION

Neovascular PSMA may be a promising marker to differentiate HCC from liver cirrhosis and a prognostic marker for anti-tumor angiogenesis therapy for HCC.

Radiolabelled PSMA PET/CT or PET/MRI in hepatocellular carcinoma (HCC): a systematic review

Introduction

Radiolabelled prostate-specific membrane antigen PSMA-based PET/CT or PET/MRI is a whole-body imaging technique usually performed for the detection of prostate cancer lesions. PSMA has been also demonstrated to be expressed by the neovasculature of many other solid tumors. The aim of this review is to evaluate the possible diagnostic role of radiolabelled PSMA PET/CT or PET/MRI in patients with hepatocellular carcinoma, by summarizing the available literature data.

Methods

A wide literature search of the PubMed/MEDLINE, Scopus, Embase and Cochrane library databases was made to find relevant published articles about the diagnostic performance of radiolabelled PSMA binding agents in PET/CT or PET/MRI imaging of patients with hepatocellular carcinoma.

Results

Ten case reports and three studies showed that hepatocellular carcinoma is PSMA-avid.

Conclusion

Radiolabelled PSMA imaging seems to be useful in analyzing hepatocellular carcinoma. Further studies enrolling a wider population are needed to clarify the real clinical and diagnostic role of radiolabelled PSMA in this setting.

Comparison of PET imaging of activated fibroblasts and 18F-FDG for diagnosis of primary hepatic tumours: a prospective pilot study

PURPOSE

This study aimed to compare the performance of ⁶⁸Ga-labelled fibroblast activating protein inhibitor (FAPI) PET and ¹⁸F-FDG PET for imaging of hepatic tumours.

METHODS

We prospectively assessed 20 patients with suspected intrahepatic lesions. Tumour radiological features, pathology, or follow-up examinations were assessed as ground truth in correlation with PET scans. Semiquantitative analysis was additionally performed by measuring the standardised uptake value (SUV). Tumour-to-liver background ratios (TBR) were calculated and compared between ⁶⁸Ga-FAPI PET and ¹⁸F-FDG PET. FAPI expression was assessed by immunochemistry in samples obtained from 7 patients with hepatocellular carcinomas (HCC)/intrahepatic cholangiocarcinoma (ICC) or granulomas.

RESULTS

Primary intrahepatic tumours, including 16 HCC in 14 patients and 4 ICC in 3 patients with extrahepatic metastases, were determined by histology (n = 14) and clinical examinations (n = 3). Based on visual analysis, 17 patients presented elevated ⁶⁸Ga-FAPI uptake (sensitivity: 100%, specificity: 100%), while 7 patients presented ¹⁸F-FDG avid tumours (sensitivity: 58.8%, specificity: 100%). ⁶⁸Ga-FAPI PET/CT identified 17 extrahepatic metastases vs. 13 in ¹⁸F-FDG PET/CT in 2 ICC patients. Three benign liver nodules in three patients showed negligible uptake in dual-PET scans. The SUV_{max_HCC} = 8.47 ± 4.06 and TBR_{max_HCC} = 7.13 ± 5.52, and SUV_{max_ICC} = 14.14 ± 2.20 TBR_{max_ICC} = 26.46 ± 4.94 in ⁶⁸Ga-FAPI-04 PET/CT were significantly higher than the ¹⁸F-FDG uptake presenting SUV_{max_HCC} = 4.86 ± 3.58 and TBR_{max_HCC} = 2.39 ± 2.21, and SUV_{max_ICC} = 9.19 ± 3.60 and TBR_{max_ICC} = 2.39 ± 2.21 (all p values < 0.05). ICC patients showed higher levels of FAPI uptake in the primary hepatic lesions compared to extrahepatic metastases, TBR_{max_ICC} = 15.18 ± 5.80 (p = 0.04).

CONCLUSIONS

⁶⁸Ga-FAPI PET-CT has superior potential in the detection of primary hepatic malignancy compared to ¹⁸F-FDG.

Incidental detection of primary hepatocellular carcinoma on 18F-prostate-specific membrane antigen-1007 positron emission tomography/computed tomography imaging in a patient with prostate cancer: A case report

RATIONALE

Prostate-specific membrane antigen positron emission tomography-computed tomography (F-PSMA-1007 PET/CT) imaging is an emerging method for the diagnosis of prostate cancer (PC), but its efficiency in detecting other accompanying diseases has rarely been investigated.

PATIENT CONCERNS

A 77-year-old man presented with a complaint of bone pain throughout his entire body lasting for 2 weeks. Routine preoperative whole-body bone scanning revealed multiple osteogenic metastases. His alpha-fetoprotein and prostate-specific antigen levels were 108.2 ng/mL and 53.32 ng/mL, respectively. F-PSMA-1007 PET/CT imaging revealed high tracer uptake in the primary lesion in the liver and the peripheral zone of the prostate.

DIAGNOSES

Due to the results from imaging and pathological examinations, a diagnosis of PC with multiple bone metastases accompanied by primary hepatocellular carcinoma was made.

INTERVENTIONS

Taking into consideration the patient's age, interventional therapy was performed for the liver lesion, whereas the prostate and bone lesions were treated with endocrine therapy.

OUTCOMES

The patient recovered well and was discharged uneventfully postoperatively. The patient was also doing well at the 6-month follow-up.

LESSONS

PSMA-PET/CT imaging results must be interpreted cautiously when the uptake of PSMA increases in a single lesion instead of the most common sites of PC metastasis. Pathological examination of the suspected lesions is also recommended.

Comparative Findings Between 68Ga-PSMA and 18F-FDG PET/CT for Hepatocellular Carcinoma

We have reported here the case of a 69-year-old man who presented with spinal cord compression due to bone metastases as the first manifestation of hepatocellular carcinoma (HCC). For the initial staging, the patient underwent ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography/computerized tomography (PET/CT) imaging, which demonstrated mild ¹⁸F-FDG uptake in the multiple expansile osteolytic bone lesions, but no remarkable atypical ¹⁸F-FDG uptake in the liver lesion on low-doses CT. An additional PET/CT scan was performed to evaluate the prostate-specific membrane antigen (PSMA) expression, which has recently been reported to be a potential biological marker in a variety of tumors including HCC. High PSMA uptake was recorded in both the metastatic bone lesions and the primary liver lesion/tumor by the ⁶⁸Ga-PSMA PET/CT.

Non-FDG PET/CT

The major applications for molecular imaging with PET in clinical practice concern cancer imaging. Undoubtedly, 18F-FDG represents the backbone of nuclear oncology as it remains so far the most widely employed positron emitter compound. The acquired knowledge on cancer features, however, allowed the recognition in the last decades of multiple metabolic or pathogenic pathways within the cancer cells, which stimulated the development of novel radiopharmaceuticals. An endless list of PET tracers, substantially covering all hallmarks of cancer, has entered clinical routine or is being investigated in diagnostic trials. Some of them guard significant clinical applications, whereas others mostly bear a huge potential. This chapter summarizes a selected list of non-FDG PET tracers, described based on their introduction into and impact on clinical practice.

[68 Ga]Ga-Prostate-Specific Membrane Antigen PET/CT: a novel method for imaging patients with hepatocellular carcinoma

Purpose

Prostate-specific membrane antigen (PSMA) is not only highly expressed on the surface prostate cancer cells but is also elevated during angiogenesis in other cancer cell types, including hepatocellular carcinoma (HCC). This study aimed to evaluate the feasibility of using PET/CT imaging with [⁶⁸Ga]Ga-PSMA-11 in HCC and its impact on patient management.

Methods

Fifteen patients (13 men and two women; aged 55.6 ± 18.2 years) with HCC were enrolled in this prospective, single-institution study. All patients underwent contrast-enhanced MRI/CT, [⁶⁸Ga]Ga-PSMA-11 PET/CT, and histopathological verification of lesions.

Results

No radiopharmaceutical-related adverse events were noted. Visual interpretation showed increased accumulation of [⁶⁸Ga]Ga-PSMA-11 in all HCC patients. The tumor-to-liver ratio (TLR) was 3.6 ± 2.1, and the maximal standardized uptake value (SUV_max) was 13.5 ± 7.1. There were no significant differences in the SUVs or TLR between newly diagnosed and recurrent patients. No statistically significant relationship was found between serum concentration of tumor markers (i.e., AFP, CA 19-9, CEA) and PET parameters. Results of the [⁶⁸Ga]Ga-PSMA-11 PET/CT changed the treatment strategy in five (33%) patients. PSMA staining showed visible heterogeneity in terms of intensity and distribution: the reaction was weak and only observed in a few vessels in pseudoglandular patterns of HCC, while it was homogeneously strong, with some hot spots, in trabecular patterns of HCC.

Conclusion

[⁶⁸Ga]Ga-PSMA-11 PET/CT can detect PSMA expression in vivo in patients with HCC and is useful for guiding treatment strategies. Further investigation of the clinical utility of this method in HCC is warranted.

The Interaction of Genomics, Molecular Imaging, and Therapy in Gastrointestinal Tumors

In the past 20 years there have been great advances in our understanding of the molecular genetics of gastrointestinal tumors. In general, cancers develop and proliferate due to: driver mutations or related alterations in the genome resulting in overactivity of oncogenes, underactivity of tumor suppressor genes allowing tumors to grow, and impaired DNA repair mechanisms either from sequential mutations with or without germline mutations predisposing patients to cancer. Infections such as hepatitis B and C, and Human Papilloma Virus (HPV) can lead to hepatocellular cancers and anal cancers, respectively. This genomic knowledge has helped us better define unique subsets within diseases like colon and pancreatic cancer which may benefit from precisely targeted therapies. Alterations in key proteins on tumors and in the tumor microenvironment can be targets for molecular-targeted radiopharmaceutical therapies, immunotherapies and other targeted treatments. Molecular imaging may be deployed more aggressively in high-risk groups for possible detection of tumor occurrence, progression, and response to therapy. This chapter provides a brief summary of the genomics of gastrointestinal tumors, selected examples of targeted therapies, and examples of how current and emerging molecular imaging tools, assessing the tumor phenotype, inform our management of patients with tumors.

Molecular Imaging and Therapy of Liver Tumors

Liver cancer is one of the top leading causes of mortality worldwide. Conventional imaging using contrast enhanced CT and MRI are currently the mainstay of oncologic imaging of the liver for the diagnosis and management of cancer. In the past two decades, especially since the advent of hybrid imaging in the form of PET/CT and SPECT/CT, molecular imaging has been increasingly utilized for oncologic imaging and the variety of radionuclide probes for imaging liver cancers have been expanding. Beyond the usual workhorse of FDG as an oncologic tracer, there is a growing body of evidence showing that radiolabeled choline tracers, C-11 acetate and other new novel tracers may have increasing roles to play for the imaging of liver tumors. On the therapy front, there have also been advances in recent times in terms of targeted therapies for both primary and secondary liver malignancies, particularly with transarterial radioembolization. The concept of theranostics can be applied to transarterial radioembolization by utilizing a pretreatment planning scan, such as Tc-99m macroaggregated albumin scintigraphy, coupled with post treatment imaging. Radiation dose planning by personalized dosimetric calculations to the liver tumors is also being advocated. This article explores the general trends in the field of nuclear medicine for the imaging and treatment of liver cancer above and beyond routine diagnosis and management.

Radiotheranostics: a roadmap for future development

Radiotheranostics, injectable radiopharmaceuticals with antitumour effects, have seen rapid development over the past decade. Although some formulations are already approved for human use, more radiopharmaceuticals will enter clinical practice in the next 5 years, potentially introducing new therapeutic choices for patients. Despite these advances, several challenges remain, including logistics, supply chain, regulatory issues, and education and training. By highlighting active developments in the field, this Review aims to alert practitioners to the value of radiotheranostics and to outline a roadmap for future development. Multidisciplinary approaches in clinical trial design and therapeutic administration will become essential to the continued progress of this evolving therapeutic approach.

Fibroblast imaging of hepatic carcinoma with 68Ga-FAPI-04 PET/CT: a pilot study in patients with suspected hepatic nodules

PURPOSE

⁶⁸Ga-FAPI-04 is a rapidly evolving PET tracer for whole-body imaging in a variety of cancers. We aimed to evaluate the diagnostic performance of ⁶⁸Ga-FAPI-04 for detecting and characterizing hepatic nodules in patients with suspected carcinoma.

METHODS

Twenty-five patients showing suspicious hepatic lesions for malignancy underwent ⁶⁸Ga-FAPI-04 PET. The maximum and mean standardised uptake values (SUV_max, SUV_mean) were measured for all detected lesions and normal hepatic tissues, respectively. The target-to-background ratio (TBR) was calculated by dividing the lesion SUV_max with the SUV_mean of non-tumour liver tissue. Lesion uptake value was correlated with the in vitro hepatic FAP expression determined by immunohistochemistry (IHC).

RESULTS

In total, 17 patients who underwent surgery or biopsy were recruited for the final analysis. A total of 28 intrahepatic malignant lesions were detected in 16 patients; the mean SUV_max was 8.36 ± 4.21 (range 2.21 to 15.86), and mean TBR was 13.15 ± 9.48 (range 2.79 to 38.12) in all detected lesions (n = 28). One benign patient showed negligible hepatic uptake (SUV_max = 0.47), whereas 75% of the primary intrahepatic hepatocellular carcinoma (HCC) lesions (n = 6) showed prominent FAP expression, 12.5% of the lesions (n = 1) showed moderate expression in stromal cells, and one showed negligible expression.

CONCLUSIONS

⁶⁸Ga-FAPI-04 showed high sensitivity in detecting hepatic malignancies, particularly in poorly differentiated forms with concordantly elevated FAP expression.

Radionuclide Therapy With 177Lu-PSMA in a Case of Metastatic Adenoid Cystic Carcinoma of the Parotid

In vivo prostate-specific membrane antigen (PSMA) overexpression creates an opportunity for PSMA-directed theranostic approach in adenoid cystic carcinoma of the parotid. Herein, we illustrate a patient with metastatic PSMA-directed theranostic approach in adenoid cystic carcinoma of the parotid who had intense PSMA uptake on metastatic lesions, followed by radionuclide therapy with Lu-PSMA.

Evidence of Prostate-Specific Membrane Antigen Expression in Hepatocellular Carcinoma Using 68Ga-PSMA PET/CT

Prostate specific membrane antigen (PSMA) expression has been demonstrated in tumor neovasculature of many solid tumors, including hepatocellular carcinoma (HCC). The purpose of this study is to evaluate PSMA expression in patients with HCC.

MATERIALS AND METHODS

Nineteen HCC patients who underwent F-fluorodeoxyglucose (F-FDG) positron emission tomography (PET) as part of restaging procedure also underwent Ga-PSMA PET. F-FDG PET and Ga-PSMA findings were compared visually as well as quantitatively using maximized standardized uptake values (SUVmax).

RESULTS

FDG was positive in 15 patients while 16 patients demonstrated PSMA expression. The only extrahepatic finding was one metastatic lymph node detected by both tracers. Mean SUVmax of liver lesions on FDG PET/CT was 8.3 ± 2.3 and mean tumor to background ratio was 2.3 ± 1.5. Respective values for Ga-PSMA PET/CT were 17.4 ± 9 and 3.3 ± 2.2. On visual and quantitative evaluation uptake was higher with PSMA in nine patients and higher with FDG in four patients. PSMA and FDG activity were similar in three patients. One of the FDG positive patients was PSMA negative whereas two patients were PSMA positive but FDG negative. Heterogeneous uptake pattern was observed in three patients. Comparison of mean SUVmax and T/B values between PET studies revealed no statistically significant difference (P > 0.1). The mean survival was 25 months (range: 18-32 months) and SUVmax of PSMA (P = 0.05) and FDG (P = 0.012) showed medium strength of correlation with overall survival.

CONCLUSION

PSMA expression in advanced HCC can be demonstrated by Ga-PSMA PET but is not superior to FDG PET however it could be useful for identifying patients with limited therapeutic options.

PSMA-Targeting Positron Emission Agents for Imaging Solid Tumors Other Than Non-Prostate Carcinoma: A Systematic Review

Despite its name, prostate-specific membrane antigen (PSMA) has been shown using immunohistochemistry (IHC) to also be over-expressed in the tumor neovasculature of a wide variety of solid tumors other than prostate carcinoma. Accordingly, positron-emitting radiolabeled small molecules targeting PSMA, initially developed for positron emission tomography in prostate carcinomas, are currently being explored for their staging and restaging potential as an alternative imaging modality in other solid tumor types where 18-F-fluorodeoxyglucose (FDG)-PET imaging has low diagnostic accuracy. In this paper, the currently available literature in this field is reviewed. Preliminary, mainly retrospective studies are encouraging, with evidence of improved diagnostic sensitivity and specificity in clear cell renal carcinoma, glioma, and hepatocellular carcinoma, leading to a change in patient management in several patients. However, the results published thus far warrant confirmation by larger prospective studies additionally assessing the longitudinal impact on patient outcomes.

Multimodality Imaging of Prostate Cancer

Prostate cancer is a very heterogeneous disease, and contemporary management is focused on identification and treatment of the prognostically adverse high-risk tumors while minimizing overtreatment of indolent, low-risk tumors. In recent years, imaging has gained increasing importance in the detection, staging, posttreatment assessment, and detection of recurrence of prostate cancer. Several imaging modalities including conventional and functional methods are used in different clinical scenarios with their very own advantages and limitations. This continuing medical education article provides an overview of available imaging modalities currently in use for prostate cancer followed by a more specific section on the value of these different imaging modalities in distinct clinical scenarios, ranging from initial diagnosis to advanced, metastatic castration-resistant prostate cancer. In addition to established imaging indications, we will highlight some potential future applications of contemporary imaging modalities in prostate cancer.

The beginning of the end for conventional RECIST - novel therapies require novel imaging approaches

Owing to improvements in our understanding of the biological principles of tumour initiation and progression, a wide variety of novel targeted therapies have been developed. Developments in biomedical imaging, however, have not kept pace with these improvements and are still mainly designed to determine lesion size alone, which is reflected in the Response Evaluation Criteria in Solid Tumors (RECIST). Imaging approaches currently used for the evaluation of treatment responses in patients with solid tumours, therefore, often fail to detect successful responses to novel targeted agents and might even falsely suggest disease progression, a scenario known as pseudoprogression. The ability to differentiate between responders and nonresponders early in the course of treatment is essential to allowing the early adjustment of treatment regimens. Various imaging approaches targeting a single dedicated tumour feature, as described in the hallmarks of cancer, have been successful in preclinical investigations, and some have been evaluated in pilot clinical trials. However, these approaches have largely not been implemented in clinical practice. In this Review, we describe current biomedical imaging approaches used to monitor responses to treatment in patients receiving novel targeted therapies, including a summary of the most promising future approaches and how these might improve clinical practice.

Prostate-specific membrane antigen expression in hepatocellular carcinoma: potential use for prognosis and diagnostic imaging

Aim

The prostate-specific membrane antigen (PSMA) is currently being established as a potent diagnostic marker in many tumor types. So far, its evidence in hepatocellular carcinoma (HCC) is sparse. The aim of our study was a comprehensive evaluation of PSMA expression and its prognostic role in patients with hepatocellular carcinoma as well as feasibility test of PSMA as an agent for diagnostic imaging.

Methods

The cohort for immunohistochemistry consisted of 153 patients with HCC. For validation purposes the HCC cohort (n = 359) of The Cancer Genome Atlas was analyzed on transcript level as well.

Results

On immunohistochemistry, non-tumorous liver tissue showed PSMA expression on canalicular membranes in all cases. In tumor tissue two patterns of expression, with a canalicular (41.1% of tumors) and a neovascular (89.9% of tumors) staining were seen. Completely negative for both two patterns were only 4.1% of tumors; conversely, 79.2% of the tumors showed high levels of PSMA protein expression at any location. At mRNA level higher FOLH1 (PSMA) expression rates were statistically significant and independently associated with longer overall survival times.Additionally, a case report of successful diagnostic ⁶⁸Ga-PSMA-11 PET/CT in a patient with HCC progression on multiple therapy lines is provided.

Conclusions

Majority of hepatocellular carcinomas show high levels of PSMA expression on tumor vessels and on canalicular membrane of the tumor cells. Putative diagnostic, prognostic and therapeutic value of PSMA in HCC warrants further clinically oriented investigations.

Gallium-68-Labeled Prostate-Specific Membrane Antigen-11 PET/CT of Prostate and Nonprostate Cancers

OBJECTIVE. The purpose of this study is to provide a concise summary of the current experience with ⁶⁸Ga-labeled prostate-specific membrane antigen (PSMA)-11 imaging of prostate and nonprostate malignancies and benign conditions. CONCLUSION. PSMA is overexpressed in prostate cancer and in the neovasculature of many other malignancies. The relevance of PSMA as a biologic target, coupled with advances in the design, synthesis, and evaluation of PSMA-based radionuclides for imaging and therapy, is anticipated to play a major role in patient care.

Expression of Prostate-Specific Membrane Antigen in Tumor-Associated Vasculature Predicts Poor Prognosis in Hepatocellular Carcinoma

INTRODUCTION

Prostate-specific membrane antigen (PSMA) was originally found to be specifically expressed in normal prostate, and its expression was upregulated in almost all stages of prostate cancer. In recent years, PSMA was also found to be expressed in tumor-associated vasculature in many nonprostatic solid tumors. However, the expression pattern of PSMA in hepatocellular carcinoma (HCC) is not well studied.

METHODS

In this study, we examined PSMA expression in 103 HCC tissues using immunohistochemical staining and analyzed the association between PSMA expression and other clinicopathological features and prognosis.

RESULTS

Among the 103 cases, 27 cases (26%) showed PSMA expression in more than 50% of tumor-associated vasculature, 49 cases (48%) showed PSMA expression in less than 50% of vasculature, and 27 cases (26%) did not have detectable PSMA expression. Vascular PSMA expression was associated with several clinicopathological features, such as tumor stage, tumor differentiation, lymph node metastasis, and Ki-67 index. Furthermore, high vascular PSMA expression was also associated with poor prognosis in patients with HCC. Univariate and multivariate analyses showed that high vascular PSMA expression can be used as an independent prognostic marker for HCC.

DISCUSSION

Our study provides the evidence that PSMA is specifically expressed in tumor-associated vasculature of HCC, and vascular PSMA expression may be used as a novel prognostic marker and a vascular therapeutic target for HCC.

One-Step 18F-Labeling and Preclinical Evaluation of Prostate-Specific Membrane Antigen Trifluoroborate Probes for Cancer Imaging

After the identification of the high-affinity glutamate-ureido scaffold, the design of several potent ¹⁸F- and ⁶⁸Ga-labeled tracers has allowed spectacular progress in imaging recurrent prostate cancer by targeting the prostate-specific membrane antigen (PSMA). We evaluated a series of PSMA-targeting probes that are ¹⁸F-labeled in a single step for PET imaging of prostate cancer. Methods: We prepared 8 trifluoroborate constructs for prostate cancer imaging, to study the influence of the linker and the trifluoroborate prosthetic on pharmacokinetics and image quality. After 1-step labeling by ¹⁹F-¹⁸F isotopic exchange, the radiotracers were injected in mice bearing LNCaP xenografts, with or without blocking controls, to assess specific uptake. PET/CT images and biodistribution data were acquired at 1 h after injection and compared with ¹⁸F-DCFPyL on the same mouse strain and tumor model. Results: All tracers exhibited nanomolar affinities, were labeled in good radiochemical yields at high molar activities, and exhibited high tumor uptake in LNCaP xenografts with clearance from nontarget organs. Most derivatives with a naphthylalanine linker showed significant gastrointestinal excretion. A radiotracer incorporating this linker with a dual trifluoroborate-glutamate labeling moiety showed high tumor uptake, low background activity, and no liver or gastrointestinal track accumulation. Conclusion: PSMA-targeting probes with trifluoroborate prosthetic groups represent promising candidates for prostate cancer imaging because of facile labeling while affording high tumor uptake values and contrast ratios that are similar to those obtained with ¹⁸F-DCFPyL.