Comparison of Prostate-Specific Membrane Antigen-Based 18F-DCFBC PET/CT to Conventional Imaging Modalities for Detection of Hormone-Naïve and Castration-Resistant Metastatic Prostate Cancer

PSMA PET/CT SUVmax as a prognostic biomarker in patients with metachronous metastatic hormone-sensitive prostate cancer (mHSPC)

BACKGROUND

Metastatic hormone-sensitive prostate cancer (mHSPC) is treatment-resistant and generally considered incurable. The development of prostate-specific membrane antigen positron emission-computed tomography (PSMA PET/CT) has generated immense expectations due to its diagnostic accuracy in prostate cancer (PCa). PSMA expression of the primary tumor, quantified by SUVmax, is a predictor of oncological outcomes. The role of PSMA-PET/CT SUVmax in metachronous mHSPC treated with ADT plus second-generation antiandrogens (ARSI) is unknown. The main aim of this study was to evaluate 68Ga-PSMA-11expression (SUVmax) as a potential prognostic biomarker in patients with metachronous mHSPC treated with ADT and first or second-generation antiandrogens. A second aim was to determine the association between PSMA SUVmax and PSA response to hormone therapy.

MATERIAL AND METHODS

Patients diagnosed with metachronous mHSPC between July 2017 and February 2023 who developed biochemical recurrence following radical surgery (with or without salvage radiotherapy and/or ADT) or external radiation therapy (with or without ADT) were included. All patients underwent 68 Ga-PSMA-11 PET/CT imaging and the SUVmax value was determined for all measurable locations. The SUVmax value was used for the semiquantitative analysis. The Wilcoxon method was used to compare responders (PSA reduction ≥ 50%) to non-responders (PSA reduction < 50%). The SUVmax value and hormone therapy were evaluated as independent variables relative to the PSA response rate or PSA reduction using the linear regression method. A mixed-effects model (ANOVA) was used for the comparisons.

RESULTS

A total of 82 patients were included. Median follow-up was 11.7 months. On the linear regression analysis, patients with a high SUVmax treated with ADT + ARSI showed a greater PSA response (p = 0.034) than those treated with ADT + first-generation antiandrogens. In the mixed-effects model, SUVmax was significant (p = 0.041). On the univariate analysis, PSA at recurrence (HR, 3.2; 95% CI: 1.07-13.6; p = 0.078) and the number of metastases (HR, 4.77; 95% CI 1.1-26.1: p = 0.002) were associated with the type of hormone therapy administered.

CONCLUSIONS

PSMA-PET/CT SUVmax is a prognostic biomarker that can be used to predict a PSA response to ADT + ARSI in patients with metachronous mHSPC. However, these findings need to be confirmed in larger prospective studies.

Medicinal (Radio) Chemistry: Building Radiopharmaceuticals for the Future

Radiopharmaceuticals are increasingly playing a leading role in diagnosing, monitoring, and treating disease. In comparison with conventional pharmaceuticals, the development of radiopharmaceuticals does follow the principles of medicinal chemistry in the context of imaging-altered physiological processes. The design of a novel radiopharmaceutical has several steps similar to conventional drug discovery and some particularity. In the present work, we revisited the insights of medicinal chemistry in the current radiopharmaceutical development giving examples in oncology, neurology, and cardiology. In this regard, we overviewed the literature on radiopharmaceutical development to study overexpressed targets such as prostate-specific membrane antigen and fibroblast activation protein in cancer; β-amyloid plaques and tau protein in brain disorders; and angiotensin II type 1 receptor in cardiac disease. The work addresses concepts in the field of radiopharmacy with a special focus on the potential use of radiopharmaceuticals for nuclear imaging and theranostics.

Comparative study of 18F-DCFPyL PET/CT and 99mTc-MDP SPECT/CT bone imaging for the detection of bone metastases in prostate cancer

Purpose

This study aimed to compare the diagnostic efficiency of 18F-DCFPyL PET/CT imaging and 99mTc-MDP SPECT/CT bone imaging for the detection of bone metastases in prostate cancer.

Methods

A retrospective analysis was conducted on 31 patients with confirmed prostate cancer between September 2020 and September 2022 at China-Japan Union Hospital of Jilin University. All patients underwent 18F-DCFPyL PET/CT and 99mTc-MDP SPECT/CT bone imaging. The gold standard was the pathology or Best Valuable Comparator (BVC) result based on clinical follow-up. Diagnostic performance indicators, including sensitivity, specificity, accuracy, positive predictive value (PPV), and negative predictive value (NPV), were analyzed at both the patient and lesion levels. The paired sample chi-square test was used to compare the two imaging methods. Receiver operating characteristic (ROC) curves were plotted, and the area under the curve (AUC) was calculated for each method. The AUC values were compared using the Z-test, and a p-value < 0.05 was considered statistically significant.

Results

Of the 31 prostate cancer patients, 18 were diagnosed with bone metastases, with a total of 84 bone metastatic lesions. At the patient level, 18F-DCFPyL PET/CT imaging showed superior diagnostic performance compared to 99mTc-MDP SPECT/CT bone imaging in all indicators: sensitivity (100% vs. 77.8%, p < 0.01), specificity (92.3% vs. 69.2%, p < 0.05), accuracy (96.8% vs. 74.2%, p < 0.01), PPV (94.7% vs. 77.8%, p < 0.01), and NPV (100% vs. 69.2%, p < 0.01). The AUC values for 18F-DCFPyL PET/CT imaging and 99mTc-MDP SPECT/CT bone imaging were 0.962 and 0.735 (Z = 2.168, p < 0.05). At the lesion level, 18F-DCFPyL PET/CT imaging showed superior diagnostic performance compared to 99mTc-MDP SPECT/CT bone imaging in all indicators: sensitivity (97.6% vs. 72.6%, p < 0.01), specificity (95.7% vs. 73.9%, p < 0.01), accuracy (97.2% vs. 72.9%, p < 0.01), PPV (98.8% vs. 91.0%, p < 0.01), and NPV (91.7% vs. 42.5%, p < 0.01). The AUC values for 18F-DCFPyL PET/CT imaging and 99mTc-MDP SPECT/CT bone imaging were 0.966 and 0.733 (Z = 3.541, p < 0.001).

Conclusion

Compared with 99mTc-MDP SPECT/CT bone imaging, 18F-DCFPyL PET/CT imaging demonstrated higher diagnostic efficiency for bone metastases in prostate cancer, and it can more accurately determine the presence of bone metastases. It is an important supplement to imaging examination for prostate cancer patients and has great potential and broad application prospects.

Traditional and novel imaging modalities for advanced prostate cancer: A critical review

Accurate detection of metastatic prostate cancer in the setting of preoperative staging as well as posttreatment recurrence is crucial to provide patients with appropriate and timely treatment of their disease. This has traditionally been accomplished with a combination of computed tomography, magnetic resonance imaging, and bone scan. Recently, more novel imaging techniques have been developed to help improve the detection of advanced and metastatic prostate cancer. This review discusses the efficacy of the traditional imaging modalities as well as the novel imaging techniques in detecting metastatic prostate cancer. Articles discussed were gathered through a formal PubMed search.

In vitro and in vivo Evaluation of Folic Acid Modified DOX-Loaded 32P-nHA Nanoparticles in Prostate Cancer Therapy

Background

Prostate cancer (PCa) ranks second in the incidence of all malignancies in male worldwide. The presence of multi-organ metastases and tumor heterogeneity often leads to unsatisfactory outcomes of conventional radiotherapy treatments. This study aimed to develop a novel folate-targeted nanohydroxyapatite (nHA) coupling to deliver adriamycin (Doxorubicin, DOX), ³²P, and ^99mTc simultaneously for the diagnosis and treatment of prostate-specific membrane antigen (PSMA) positive prostate cancer.

Methods

The spherical nHA was prepared by the biomimetic method and characterized. Folic acid (FA) was coupled to nHA with polyethylene glycol (PEG), and the grafting ratio of PEG-nHA and FA-PEG-nHA was determined by the thermogravimetric analysis (TGA) method. In addition, ³²P, ^99mTc, and DOX were loaded on nHA by physisorption. And the labeling rate and stability of radionuclides were measured by a γ-counter. The loading and release of DOX at different pH were determined by the dialysis method. Targeting of FA-PEG-nHA loaded with ^99mTc was verified by in vivo SPECT imaging. In vitro anti-tumor effect of ³²P/DOX-FA-PEG-nHA was assessed with apoptosis assay. The safety of the nano-drugs was verified by histopathological analysis.

Results

The SEM images showed that the synthesized nHA was spherical with uniform particle size (average diameter of about 100nm). The grafting ratio is about 10% for PEG and about 20% for FA. The drug loading and the delayed release of DOX at different pH confirmed its long-term therapeutic ability. The labeling of ³²P and ^99mTc was stable and the labeling rate was great. SPECT showed that FA-PEG-nHA showed well in vivo tumor targeting and less damage to normal tissues.

Conclusion

FA-targeted nHA loaded with ³²P, ^99mTc, and DOX may be a new diagnostic and therapeutic strategy for targeting PSMA-positive prostate cancer tumors, which may achieve better therapeutic results while circumventing the severe toxic side effects of conventional chemotherapeutic agents.

Incorporating Prostate-specific Membrane Antigen Positron Emission Tomography in Management Decisions for Men with Newly Diagnosed or Biochemically Recurrent Prostate Cancer

CONTEXT

Prostate-specific membrane antigen (PSMA) is a promising molecular target for prostate cancer (PCa) that has allowed the development of a novel diagnostic approach to PCA in the primary and recurrent settings.

OBJECTIVE

To summarize available data and recommendations regarding the use of PSMA in newly diagnosed and recurrent PCa via a narrative review.

EVIDENCE ACQUISITION

A literature review was conducted using MEDLINE (via PubMed) and Scopus. The search strategy included meta-analyses, reviews, and original studies on staging and restaging with ⁶⁸Ga-PSMA positron emission tomography (PET)/computed tomography (CT).

EVIDENCE SYNTHESIS

Studies comparing PSMA-targeted imaging and conventional imaging suggest superior performance of PSMA-targeted imaging in primary and recurrent PCa, albeit with several clinically relevant limitations. Pretreatment ⁶⁸Ga-PSMA PET/CT allowed more accurate PCa staging in compared to routine practice for high-risk cases, and identified a number of otherwise unknown metastatic lesions. In biochemically recurrent PCa, PSMA PET can reveal sites of recurrence with greater sensitivity and specificity than conventional imaging, potentially detecting a major proportion of occult disease. This review will help providers in applying the most up-to-date and relevant literature to (1) determine which patients truly have oligometastatic disease and (2) ascertain who is most likely to experience a meaningful response to local consolidation in the biochemical recurrence setting.

CONCLUSIONS

Data on PSMA diagnostic studies in primary and recurrent PCa highlight the accuracy and clinical application of PSMA PET. While this review and the evidence to date might lead to a perception of superiority in metastasis directed therapy, fundamental lack of phase III clinical trials with clinically meaningful outcomes are yet to be determined.

PATIENT SUMMARY

PSMA (prostate-specific membrane antigen) scans have shown great promise for initial evaluation of prostate cancer (PCa) and in detection of PCa recurrence. The benefits are more apparent for initial staging of PCa. There are more limited clinical trial results for PCa recurrence on how best to use this new technique to guide cancer treatment.

Prostate-Specific Membrane Antigen-Based PET Brings New Insights into the Management of Prostate Cancer

Prostate cancer (PCa) is the third most common cancer diagnosed in the world. Since its first identification in 1987 and its first molecular cloning in 1993, prostate-specific membrane antigen (PSMA) has been developed as a theragnostic imaging biomarker and therapeutic agent for PCa. For metastatic castration-resistant PCa, PSMA-based PET imaging can be applied to the monitoring of disease and response assessment with PSMA-based therapeutics. This novel imaging modality is bringing new insights into diagnosis, stratification, and clinical decision-making and treatment.

Current role of prostate-specific membrane antigen-based imaging and radioligand therapy in castration-resistant prostate cancer

Castration-resistant prostate cancer (CRPC) is a therapy-resistant and lethal form of prostate cancer as well as a therapeutic challenge. Prostate-specific membrane antigen (PSMA) has been proved as a promising molecular target for optimizing the theranostics for CRPC patients. When combined with PSMA radiotracers, novel molecular imaging techniques such as positron emission tomography (PET) can provide more accurate and expedient identification of metastases when compared with conventional imaging techniques. Based on the PSMA-based PET scans, the accurate visualization of local and disseminative lesions may help in metastasis-directed therapy. Moreover, the combination of ⁶⁸Ga-labeled PSMA-based PET imaging and radiotherapy using PSMA radioligand therapy (RLT) becomes a novel treatment option for CRPC patients. The existing studies have demonstrated this therapeutic strategy as an effective and well-tolerated therapy among CRPC patients. PSMA-based PET imaging can accurately detect CRPC lesions and describe their molecular features with quantitative parameters, which can be used to select the best choice of treatments, monitor the response, and predict the outcome of RLT. This review discussed the current and potential role of PSMA‐based imaging and RLT in the diagnosis, treatment, and prediction of prognosis of CRPC.

Predictors of 18F-DCFPyL PET/CT Positivity in Patients with Biochemical Recurrence of Prostate Cancer After Local Therapy

Our objective was to investigate the factors predicting scan positivity and disease location in patients with biochemical recurrence (BCR) of prostate cancer (PCa) after primary local therapy using prostate-specific membrane antigen-targeted ¹⁸F-DCFPyL PET/CT. Methods: This was a 2-institution study including 245 BCR PCa patients after primary local therapy and negative results on conventional imaging. The patients underwent ¹⁸F-DCFPyL PET/CT. We tested for correlations of lesion detection rate and disease location with tumor characteristics, time from initial therapy, prostate-specific antigen (PSA) level, and PSA doubling time (PSAdt). Multivariate logistic regression analyses were used to determine predictors of a positive scan. Regression-based coefficients were used to develop nomograms predicting scan positivity and extrapelvic disease. Results: Overall, 79.2% (194/245) of patients had a positive ¹⁸F-DCFPyL PET/CT result, with detection rates of 48.2% (27/56), 74.3% (26/35), 84% (37/44), 96.7% (59/61), and 91.8% (45/49) for PSAs of <0.5, 0.5 to <1.0, 1.0 to <2.0, 2.0 to <5.0, and ≥5.0 ng/mL, respectively. Patients with lesions confined to the pelvis had lower PSAs than those with distant sites (1.6 ± 3.5 vs. 3.0 ± 6.3 ng/mL, P < 0.001). In patients treated with prostatectomy (n = 195), 24.1% (47/195) had a negative scan result, 46.1% (90/195) showed intrapelvic disease, and 29.7% (58/195) showed extrapelvic disease. In the postradiation subgroup (n = 50), ¹⁸F-DCFPyL PET/CT was always negative at a PSA lower than 1.0 ng/mL and extrapelvic disease was seen only when PSA was greater than 2.0 ng/mL. At multivariate analysis, PSA and PSAdt were independent predictive factors of scan positivity and the presence of extrapelvic disease in postsurgical patients, with area under the curve of 78% and 76%, respectively. PSA and PSAdt were independent predictors of the presence of extrapelvic disease in the postradiation cohort, with area under the curve of 85%. Time from treatment to scan was significantly longer for prostatectomy-bed-only recurrences than for those with bone or visceral disease (6.2 ± 6.4 vs. 2.4 ± 1.3 y, P < 0.001). Conclusion:¹⁸F-DCFPyL PET/CT offers high detection rates in BCR PCa patients. PSA and PSAdt are able to predict scan positivity and disease location. Furthermore, the presence of bone or visceral lesions is associated with shorter intervals from treatment than are prostate-bed-only recurrences. These tools might guide clinicians to select the most suitable candidates for ¹⁸F-DCFPyL PET/CT imaging.

The History of Prostate-Specific Membrane Antigen as a Theranostic Target in Prostate Cancer: The Foundational Role of the Prostate Cancer Foundation

Prostate-Specific Membrane Antigen (PSMA) is a credentialed imaging and therapy (theranostic) target for the detection and treatment of prostate cancer. PSMA-targeted positron emission tomography (PET) imaging and molecular radiotherapy (MRT) are promising evolving technologies that will improve the outcomes of prostate cancer patients. In anticipation of this new era in prostate cancer theranostics, this article will review the history of PSMA from discovery, through early and late stage clinical trials. Since 1993, the Prostate Cancer Foundation (PCF) has funded critical and foundational PSMA research that established this theranostic revolution. The history and role of PCF funding in this field will be discussed.

Value of PET imaging for radiation therapy

This comprehensive review written by experts in their field gives an overview on the current status of incorporating positron emission tomography (PET) into radiation treatment planning. Moreover, it highlights ongoing studies for treatment individualisation and per-treatment tumour response monitoring for various primary tumours. Novel tracers and image analysis methods are discussed. The authors believe this contribution to be of crucial value for experts in the field as well as for policy makers deciding on the reimbursement of this powerful imaging modality.

Value of PET imaging for radiation therapy

This comprehensive review written by experts in their field gives an overview on the current status of incorporating positron emission tomography (PET) into radiation treatment planning. Moreover, it highlights ongoing studies for treatment individualisation and per-treatment tumour response monitoring for various primary tumours. Novel tracers and image analysis methods are discussed. The authors believe this contribution to be of crucial value for experts in the field as well as for policy makers deciding on the reimbursement of this powerful imaging modality.

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.

Role of 18F-Fluciclovine and Prostate-Specific Membrane Antigen PET/CT in Guiding Management of Oligometastatic Prostate Cancer: AJR Expert Panel Narrative Review

Twenty-five years ago, oligometastatic disease was proposed as an intermediary clinical state of cancer with unique implications for therapies that may impact cancer evolution and patient outcome. Identification of limited metastases that are potentially amenable to targeted therapies fundamentally depends on the sensitivity of diagnostic tools, including new-generation imaging methods. For men with biochemical recurrence after definitive therapy of the primary prostate cancer, PET/CT using either the FDA-approved radiolabeled amino acid analogue ¹⁸F-fluciclovine or investigational radiolabeled agents targeting prostate-specific membrane antigen (PSMA) enables identification of early metastases at lower serum PSA levels than was previously feasible using conventional imaging. Evidence supports PSMA PET/CT as the most sensitive imaging modality available for identifying disease sites in oligometastatic prostate cancer. PSMA PET/CT will likely become the modality of choice after regulatory approval and will drive the development of trials of emerging metastasis-directed therapies such as stereotactic ablative body radiation and radioguided surgery. Indeed, numerous ongoing or planned clinical trials are studying advances in management of oligometastatic prostate cancer based on this heightened diagnostic capacity. In this rapidly evolving clinical environment, radiologists and nuclear medicine physicians will play major roles in facilitating clinical decision making and management of patients with oligometastatic prostate cancer.

Recent updates and developments in PET imaging of prostate cancer

A number of positron emission tomography (PET) radiotracers have been developed to improve the sensitivity and specificity of imaging for prostate cancer. These radiotracers include the bone-seeking agent Na¹⁸F as well as more tumor-specific compounds such as ¹¹C-choline and ¹⁸F-fluciclovine. In this review, we will discuss the advantages and disadvantages of these PET radiotracers for the imaging of men with prostate cancer across a range of clinical contexts. We will also touch upon radiotracers in late clinical development that have not gained regulatory approval, including those targeted against prostate-specific membrane antigen (PSMA) and gastrin-releasing peptide receptor (GRPR).

Toward the Discovery and Development of PSMA Targeted Inhibitors for Nuclear Medicine Applications

BACKGROUND

The rising incidence rate of prostate cancer (PCa) has promoted the development of new diagnostic and therapeutic radiopharmaceuticals during the last decades. Promising improvements have been achieved in clinical practice using prostate specific membrane antigen (PSMA) labeled agents, including specific antibodies and small molecular weight inhibitors. Focusing on molecular docking studies, this review aims to highlight the progress in the design of PSMA targeted agents for a potential use in nuclear medicine.

RESULTS

Although the first development of radiopharmaceuticals able to specifically recognize PSMA was exclusively oriented to macromolecule protein structure such as radiolabeled monoclonal antibodies and derivatives, the isolation of the crystal structure of PSMA served as the trigger for the synthesis and the further evaluation of a variety of low molecular weight inhibitors. Among the nuclear imaging probes and radiotherapeutics that have been developed and tested till today, labeled Glutamate-ureido inhibitors are the most prevalent PSMA-targeting agents for nuclear medicine applications.

CONCLUSION

PSMA represents for researchers the most attractive target for the detection and treatment of patients affected by PCa using nuclear medicine modalities. [99mTc]MIP-1404 is considered the tracer of choice for SPECT imaging and [68Ga]PSMA-11 is the leading diagnostic for PET imaging by general consensus. [18F]DCFPyL and [18F]PSMA-1007 are clearly the emerging PET PSMA candidates for their great potential for a widespread commercial distribution. After paving the way with new imaging tools, academic and industrial R&Ds are now focusing on the development of PSMA inhibitors labeled with alpha or beta minus emitters for a theragnostic application.

Bone scintigraphy as a gatekeeper for the detection of bone metastases in patients with prostate cancer: comparison with Ga-68 PSMA PET/CT

OBJECTIVES

Gallium-68-labeled prostate-specific membrane antigen (Ga-PSMA) positron emission tomography (PET)/computed tomography (CT) is a valuable diagnostic tool for the detection of bone metastases in patients with prostate cancer (PCa). However, bone scintigraphy (BS) with technetium-labeled diphosphonates is cheap and widely available for the same patient population. PSMA PET comes with a cost, and financial constraints in the present economic environment may require its more selective use. In this study, we aimed to compare the diagnostic performance of BS with Ga-PSMA PET/CT for the detection of bone metastases in patients with PCa and correlate the results with various clinical and biochemical variables.

MATERIALS AND METHODS

Ninety-five patients who underwent Ga-PSMA PET/CT and BS within 3 months for newly diagnosed or recurrent PCa were extracted from our database. Lesion, region and patient-based analyses were performed. Clinical and imaging follow-up was used as the reference test. Results were compared with tumor grade, serum prostate-specific antigen (PSA), and alkaline phosphatase (ALP) values.

RESULTS

On the patient-based analysis, 75% (42/56) and 98.2% (55/56) of the patients with bone metastases were correctly diagnosed by BS and Ga-PSMA PET, respectively. In 26/95 patients with equivocal lesions on BS, Ga-PSMA PET correctly reclassified skeletal involvement in 11 and excluded metastases in 15 patients BS missed bone metastases in 3 patients. The true-positive rate of BS in patients with serum ALP ≥ 120U/L and PSA ≥ 50 ng/ml was 95.8% and 87.5 respectively.

CONCLUSION

Ga-PSMA is superior to BS for the evaluation of metastatic disease in patients with PCa. However, BS can also detect bone metastases in patients with PCa with a minimum sensitivity of 75%. Biochemical data are helpful to select patients with a high pretest probability who should undergo BS first as a part of the initial workup from an economic point of view. Due to its higher cost, Ga-PSMA PET should be performed in a selective group of patients when BS results are inconclusive or metastasis-directed therapy is planned.

Reporting and handling of equivocal imaging findings in diagnostic studies of bone metastasis in prostate cancer

BACKGROUND

Equivocal scanning results occur. It remains unclear how these results are presented and their management influence diagnostic characteristics.

PURPOSE

To investigate the reporting and handling of equivocal imaging findings in diagnostic studies of bone metastases, and to assess the impact on diagnostic performance of the methods used to analyze equivocal findings. The conceptual issue was reified based on two actual observations.

MATERIAL AND METHODS

A recent meta-analysis of bone metastases in prostate cancer was conducted and data were obtained from a large clinical trial with a true reference of bone metastasis, where diagnostic characteristics were calculated with equivocal scans handled by: removal; considered malignant; considered benign; and intention-to-diagnose.

RESULTS

The meta-analysis included 18 trials where the median proportion of reported equivocal results was 27%. Eleven (61%) studies reported an equivocal option for the index test, 42% reported equivocal results and described how these were analyzed. The clinical trial included 583 prostate cancer patients with 20% equivocal results. The different methods of managing equivocal findings resulted in highly variable outcomes: sensitivity = 85%-100%; specificity = 78%-99%; and positive and negative predictive values = 44%-94% and 97%-100%, respectively. The diagnostic performances obtained using the four methods were differentially susceptible to the proportion of equivocal imaging findings and the prevalence of bone metastases.

CONCLUSION

Reporting of equivocal results was inadequate in bone imaging trials. The handling of equivocal findings strongly influenced diagnostic accuracy.

Positron emission tomography (PET) radiotracers for prostate cancer imaging

Imaging plays an increasing role in prostate cancer diagnosis and staging. Accurate staging of prostate cancer is required for optimal treatment planning. In detecting extraprostatic cancer and sites of early recurrence, traditional imaging methods (computed tomography, magnetic resonance imaging, radionuclide bone scan) have suboptimal performance. This leaves a gap between known disease recurrence as indicated by rising prostate-specific antigen and the ability to localize the recurrence on imaging. Novel positron emission tomography (PET) agents including radiolabeled choline, fluciclovine (¹⁸F-FACBC), and agents targeting prostate-specific membrane antigen are being developed and tested to increase diagnostic performance of non-invasive prostate cancer localization. When combined with CT or MRI, these tracers offer a combination of functional information and anatomic localization that is superior to conventional imaging methods. These PET radiotracers have varying mechanisms and excretion patterns affecting their pharmacokinetics and diagnostic performance, which will be reviewed in this article.

Prostate-Specific Membrane Antigen-Targeted Radiopharmaceuticals in Diagnosis and Therapy of Prostate Cancer: Current Status and Future Perspectives

Prostate cancer is the most common cancer to affect men in the United States and the second most common cancer in men worldwide. Prostate-specific membrane antigen (PSMA)-based positron emission tomography (PET) imaging has become increasingly popular as a novel molecular imaging technique capable of improving the clinical management of patients with prostate cancer. To date, several ⁶⁸Ga and ¹⁸F-labeled PSMA-targeted molecules have shown promising results in imaging patients with recurrent prostate cancer using PET/computed tomography (PET/CT). Studies of involving PSMA-targeted radiopharmaceuticals also suggest a higher sensitivity and specificity, along with an improved detection rate over conventional imaging (CT scan and methylene diphosphonate bone scintigraphy) and ¹¹C/¹⁸F-choline PET/CT. In addition, PSMA-617 and PSMA I&T ligands can be labeled with α- and β-emitters (e.g., ²²⁵Ac, ⁹⁰Y, and ¹⁷⁷Lu) and serve as a theranostic tool for patients with metastatic prostate cancer. While the clinical impact of such concept remains to be verified, the preliminary results of PSMA molecular radiotherapy are very encouraging. Herein, we highlighted the current status of development and future perspectives of PSMA-targeted radiopharmaceuticals and their clinical applications.

Comparison of cross-sectional imaging techniques for the detection of prostate cancer lymph node metastasis: a critical review

Conventional staging for prostate cancer (PCa) is performed for men diagnosed with unfavorable-intermediate or higher risk disease. Computed tomography (CT) of the abdomen and pelvis and whole body bone scan remains the standard of care for the detection of visceral, nodal, and bone metastasis. The implementation of the 2012 United States Preventive Services Task Force recommendation against routine prostate specific antigen (PSA) screening resulted in a rise of metastatic PCa at the time of diagnosis, emphasizing the importance of effective imaging modalities for evaluating metastatic disease. CT plays a major role in clinical staging at the time of PCa diagnosis, but multi-parametric magnetic resonance imaging (MRI) is now integrated into many prostate biopsy protocols for the detection of primary PCa, and may be a surrogate for CT for nodal staging. Current guidelines incorporate both CT and MRI as appropriate cross-sectional imaging modalities for the identification of nodal metastasis in indicated patients. There is an ongoing debate about the utility of traditional cross-sectional imaging modalities as well as advanced imaging modalities in detection of both organ-confined PCa detection and nodal involvement.

Uptake of prostate-specific membrane antigen-targeted 18F-DCFPyL in avascular necrosis of the femoral head

In recent years, the emergence of prostate-specific membrane antigen (PSMA)-targeted positron-emission tomography (PET) imaging has brought about a paradigm shift in the way that prostate cancer (PCa) is imaged in many parts of the world. Although PSMA-targeted PET imaging has been demonstrated to be a highly sensitive and specific imaging modality for the identification of sites of PCa, its clinical utility hinges on the ability of imaging specialists and their clinical colleagues to recognize potential false-positive sources of uptake and to tailor therapy based on that recognition. In this manuscript, we report the case of a 74-year-old male with a history of recurrent PCa who was referred for a restaging PSMA-targeted ¹⁸F-DCFPyL PET/computed tomography (PET/CT). PET images demonstrated low level but focal and definitive uptake in the left femoral head. This uptake corresponded to sclerotic changes on CT whose morphology was most compatible with avascular necrosis without femoral head collapse. In the presented case, the integrated assessment of the CT imaging together with the PET findings was fundamental to avoid misinterpretation of the left femur finding as metastatic disease, which would have ultimately altered the clinical management of the patient.

Current Status of PSMA-Radiotracers for Prostate Cancer: Data Analysis of Prospective Trials Listed on ClinicalTrials.gov

The recent development of dedicated prostate-specific membrane antigen (PSMA) targeted radioligands shows the potential to change and improve the diagnosis and therapy of prostate cancer. There is an increasing number of prospective trials to further establish these tracers in the clinical setting. We analyzed data from the ClinicalTrials.gov registry including all listed prospective trials with PSMA-ligands for prostate cancer as of October 2019 concerning the different tracers and study characteristics. We found n = 104 eligible studies with a total of n = 25 different tracers in use: most frequently [⁶⁸Ga]Ga-PSMA-11 (32%), followed by [¹⁸F]DCFPyL (24%) and [¹⁷⁷Lu]Lu-PSMA-617 (10%). 85% are single-center, 15% multi-center studies. 95% national and 5% international studies. 34% are phase-II, 24% phase-I, 13% phase-I/-II, 12% phase-II/-III and phase-III and 7% early-phase-I. The primary purpose was classified as diagnostic in 72% of cases and therapeutic in 23% of cases. Most studies were executed in the USA (70%), followed by Canada (13%) and France (6%). This quantitative descriptive registry analysis indicates the rapid and global clinical developments and current status of PSMA-radioligands with emphasis on radiopharmaceutical and organizational aspects. It will be very interesting to see which tracers will prevail in the clinical setting.

18F-Labeled, PSMA-Targeted Radiotracers: Leveraging the Advantages of Radiofluorination for Prostate Cancer Molecular Imaging

Prostate-specific membrane antigen (PSMA)-targeted PET imaging for prostate cancer with 68Ga-labeled compounds has rapidly become adopted as part of routine clinical care in many parts of the world. However, recent years have witnessed the start of a shift from 68Ga- to 18F-labeled PSMA-targeted compounds. The latter imaging agents have several key advantages, which may lay the groundwork for an even more widespread adoption into the clinic. First, facilitated delivery from distant suppliers expands the availability of PET radiopharmaceuticals in smaller hospitals operating a PET center but lacking the patient volume to justify an onsite 68Ge/68Ga generator. Thus, such an approach meets the increasing demand for PSMA-targeted PET imaging in areas with lower population density and may even lead to cost-savings compared to in-house production. Moreover, 18F-labeled radiotracers have a higher positron yield and lower positron energy, which in turn decreases image noise, improves contrast resolution, and maximizes the likelihood of detecting subtle lesions. In addition, the longer half-life of 110 min allows for improved delayed imaging protocols and flexibility in study design, which may further increase diagnostic accuracy. Moreover, such compounds can be distributed to sites which are not allowed to produce radiotracers on-site due to regulatory issues or to centers without access to a cyclotron. In light of these advantageous characteristics, 18F-labeled PSMA-targeted PET radiotracers may play an important role in both optimizing this transformative imaging modality and making it widely available. We have aimed to provide a concise overview of emerging 18F-labeled PSMA-targeted radiotracers undergoing active clinical development. Given the wide array of available radiotracers, comparative studies are needed to firmly establish the role of the available 18F-labeled compounds in the field of molecular PCa imaging, preferably in different clinical scenarios.

Fibrous dysplasia as a possible false-positive finding in 68Ga-labeled prostate-specific membrane antigen positron emission tomography/computed tomography study in the follow-up of prostate cancer

Positron emission tomography/computed tomography (PET/CT) using ⁶⁸Ga-labeled prostate-specific membrane antigen (⁶⁸Ga-PSMA) has become an important tool in restaging patients with prostate cancer (PCa). Despite its high sensitivity and specificity, this method may produce false-positive findings, as indicated by previous studies. This case report aims to warn nuclear medicine physicians, oncologists, and urologists about the possibility of false-positive findings using this imaging modality, especially when the detected site is unusual for bone metastasis. A 68-year-old man with PCa underwent restaging tests after presenting with increased prostate-specific antigen. ⁶⁸Ga-PSMA PET/CT imaging revealed abnormal uptake in the left humeral head, which anatomically corresponded to the intramedullary and cortical sclerotic area. A biopsy was performed, and the pathology showed a lesion consisting of hard bone tissue with a small focal spot of fibrous dysplasia. Diagnostic issues related to ⁶⁸Ga-PSMA PET/CT imaging should be disseminated to help physicians make appropriate treatment choices for each patient.

18F-DCFPyL PET/CT Imaging in Patients with Biochemically Recurrent Prostate Cancer After Primary Local Therapy

Our objective was to investigate the lesion detection rate of ¹⁸F-DCFPyL PET/CT, a prostate-specific membrane antigen (PSMA)-targeted PET agent, in patients with biochemically relapsed prostate cancer after primary local therapy. Methods: This was a prospective institutional review board-approved study of 90 patients with documented biochemical recurrence (median prostate-specific antigen [PSA], 2.5 ng/mL; range, 0.21-35.5 ng/mL) and negative results on conventional imaging after primary local therapies, including radical prostatectomy (n = 38), radiation (n = 27), or a combination of the two (n = 25). Patients on androgen deprivation therapy were excluded. Patients underwent whole-body ¹⁸F-DCFPyL PET/CT (299.9 ± 15.5 MBq) at 2 h after injection. The PSMA PET lesion detection rate was correlated with PSA, PSA kinetics, and original primary tumor grade. Results: Seventy patients (77.8%) showed positive PSMA PET results, with a total of 287 lesions identified: 37 prostate bed foci, 208 lesions in lymph nodes, and 42 in distant sites in bones or organs, Eleven patients had negative results, and 9 patients showed indeterminate lesions, which were considered negative in this study. The detection rates were 47.6% (n = 10/21), 50% (n = 5/10), 88.9% (n = 8/9), and 94% (n = 47/50) for PSA levels of >0.2 to <0.5, 0.5 to <1.0, 1 to <2.0, and ≥2.0 ng/mL, respectively. In postsurgical patients, PSA, PSA doubling time, and PSA velocity correlated with PET results, but the same was not true for postradiation patients. These parameters also correlated with the extent of disease on PET (intrapelvic vs. extrapelvic). There was no significant difference in the rate of positive scans between patients with higher-grade and lower-grade primary tumors (Gleason score of ≥4 + 3 vs. <3 + 4). Tumor recurrence was histology-confirmed in 40% (28/70) of patients. On a per-patient basis, positive predictive value was 93.3% (95% confidence interval, 77.6%-99.2%) by histopathologic validation and 96.2% (95% confidence interval, 86.3%-99.7%) by the combination of histology and imaging/clinical follow-up. Conclusion: ¹⁸F-DCFPyL PET/CT imaging offers high detection rates in biochemically recurrent prostate cancer patients and is positive in about 50% of patients with a PSA level of less than 0.5 ng/mL, which could substantially impact clinical management. In postsurgical patients, ¹⁸F-DCFPyL PET/CT correlates with PSA, PSA doubling time, and PSA velocity, suggesting it may have prognostic value. ¹⁸F-DCFPyL PET/CT is highly promising for localizing sites of recurrent prostate cancer.

Prospective Comparison of PET Imaging with PSMA-Targeted 18F-DCFPyL Versus Na18F for Bone Lesion Detection in Patients with Metastatic Prostate Cancer

Bone metastases in prostate cancer (PCa) have important prognostic significance, and imaging modalities used for PCa staging should have high sensitivity for detecting such lesions. Prostate-specific membrane antigen (PSMA)-targeted PET radiotracers are promising new agents for imaging PCa. We undertook a head-to-head comparison of PSMA-targeted 2-(3-{1-carboxy-5-[(6-¹⁸F-fluoro-pyridine-3-carbonyl)-amino]-pentyl}-ureido)-pentanedioic acid (¹⁸F-DCFPyL) PET to Na¹⁸F PET to determine which modality was more sensitive for the detection of lesions suggestive of bone metastases in a group of patients with metastatic PCa. Methods: Patients with progressive, metastatic PCa were prospectively imaged with both ¹⁸F-DCFPyL and Na¹⁸F PET/CT, with both scans occurring within 24 h of each other. A consensus 2-reader central review was performed to identify all bone lesions suggestive of sites of PCa involvement on both scans, and maximized SUVs corrected for body weight (SUV_max) and lean body mass (SUL_max) were recorded. Soft-tissue lesions were also noted on both scans, and SUV_max, SUL_max, and PSMA reporting and data system (RADS) version 1.0 scores were recorded. Data from the 2 scans were compared using a generalized estimating equation. Results: In total, 16 patients meeting all inclusion criteria were enrolled in this study, and 15 of the 16 (93.8%) were imaged with both PET radiotracers. In total, 405 bone lesions suggestive of sites of PCa were identified on at least 1 scan. On ¹⁸F-DCFPyL PET/CT, 391 (96.5%) were definitively positive, 4 (1.0%) were equivocally positive, and 10 (2.5%) were negative. On Na¹⁸F PET/CT, the corresponding values were 388 (95.8%), 4 (1.0%), and 13 (3.2%). Of the definitively negative lesions on ¹⁸F-DCFPyL PET, 8 of 10 (80.0%) were sclerotic and 2 of 10 (20.0%) were infiltrative or marrow-based. Additionally, 12 of 13 (92.3%) of the definitively negative lesions on Na¹⁸F PET were infiltrative or marrow-based and 1 of 13 (7.7%) was lytic. Also identified were 78 PSMA-RADS-4, 17 PSMA-RADS-5, and 1 PSMA-RADS-3C soft-tissue lesions. Conclusion: PET/CT imaging using ¹⁸F-DCFPyL and Na¹⁸F PET had nearly identical sensitivities for the detection of bone lesions in patients with metastatic PCa. As would be expected, PSMA-targeted PET provides more information on soft-tissue disease. There may be little additional value to imaging PCa patients with Na¹⁸F after a PSMA-targeted PET scan has already been performed.

177Lu-labeled low-molecular-weight agents for PSMA-targeted radiopharmaceutical therapy

PURPOSE

To develop a prostate-specific membrane antigen (PSMA)-targeted radiotherapeutic for metastatic castration-resistant prostate cancer (mCRPC) with optimized efficacy and minimized toxicity employing the β-particle radiation of ¹⁷⁷Lu.

METHODS

We synthesized 14 new PSMA-targeted, ¹⁷⁷Lu-labeled radioligands (¹⁷⁷Lu-L1-¹⁷⁷Lu-L14) using different chelating agents and linkers. We evaluated them in vitro using human prostate cancer PSMA(+) PC3 PIP and PSMA(-) PC3 flu cells and in corresponding flank tumor models. Efficacy and toxicity after 8 weeks were evaluated at a single administration of 111 MBq for ¹⁷⁷Lu-L1, ¹⁷⁷Lu-L3, ¹⁷⁷Lu-L5 and ¹⁷⁷Lu-PSMA-617. Efficacy of ¹⁷⁷Lu-L1 was further investigated using different doses, and long-term toxicity was determined in healthy immunocompetent mice.

RESULTS

Radioligands were produced in high radiochemical yield and purity. Cell uptake and internalization indicated specific uptake only in PSMA(+) PC3 cells. ¹⁷⁷Lu-L1, ¹⁷⁷Lu-L3 and ¹⁷⁷Lu-L5 demonstrated comparable uptake to ¹⁷⁷Lu-PSMA-617 and ¹⁷⁷Lu-PSMA-I&T in PSMA-expressing tumors up to 72 h post-injection. ¹⁷⁷Lu-L1, ¹⁷⁷Lu-L3 and ¹⁷⁷Lu-L5 also demonstrated efficient tumor regression at 8 weeks. ¹⁷⁷Lu-L1 enabled the highest survival rate. Necropsy studies of the treated group at 8 weeks revealed subacute damage to lacrimal glands and testes. No radiation nephropathy was observed 1 year post-treatment in healthy mice receiving 111 MBq of ¹⁷⁷Lu-L1, most likely related to the fast renal clearance of this agent.

CONCLUSIONS

¹⁷⁷Lu-L1 is a viable clinical candidate for radionuclide therapy of PSMA-expressing malignancies because of its high tumor-targeting ability and low off-target radiotoxic effects.

Deformable registration of PET/CT and ultrasound for disease-targeted focal prostate brachytherapy

We propose a deformable registration algorithm for prostate-specific membrane antigen (PSMA) PET/CT and transrectal ultrasound (TRUS) fusion. Accurate registration of PSMA PET to intraoperative TRUS will allow physicians to customize dose planning based on the regions involved. The inputs to the registration algorithm are the PET/CT and TRUS volumes as well as the prostate segmentations. PET/CT and TRUS volumes are first rigidly registered by maximizing the overlap between the segmented prostate binary masks. Three-dimensional anatomical landmarks are then automatically extracted from the boundary as well as within the prostate. Then, a deformable registration is performed using a regularized thin plate spline where the landmark localization error is optimized between the extracted landmarks that are in correspondence. The proposed algorithm was evaluated on 25 prostate cancer patients treated with low-dose-rate brachytherapy. We registered the postimplant CT to TRUS using the proposed algorithm and computed target registration errors (TREs) by comparing implanted seed locations. Our approach outperforms state-of-the-art methods, with significantly lower ( mean ± standard deviation ) TRE of 1.96 ± 1.29    mm while being computationally efficient (mean computation time of 38 s). The proposed landmark-based PET/CT-TRUS deformable registration algorithm is simple, computationally efficient, and capable of producing quality registration of the prostate boundary as well as the internal gland.

PSMA-Targeted Radiopharmaceuticals for Imaging and Therapy

As described in more detail in other contributions in this issue of Seminars in Nuclear Medicine, prostate-specific membrane antigen (PSMA) has become one of the most promising molecular targets in nuclear medicine. Due to its overexpression on prostate cancer cells in proportion to the stage and grade of tumour progression, especially in androgen-independent, advanced and metastatic disease, various tracers for the detection and treatment of prostate cancer by means of radioligand imaging, radioligand therapy or radioguided surgery have been developed and transferred to clinical applications. Even though monoclonal antibodies were investigated and introduced as first PSMA-targeted probes, the inherent advantage of fast tumour uptake and rapid excretion of small molecules has shifted the research focus during the last decade to low molecular weight inhibitors with high affinity to PSMA, such as [¹⁸F]FDCFPyL, [¹⁸F]PSMA-1007, [⁶⁸Ga]PSMA-HBED, [¹⁷⁷Lu]PSMA-617, [¹⁷⁷Lu]PSMA-I&T, [^99mTc]MIP-1404 or [^99mTc]PSMA I&S, to mention only a few. Due to the plethora of such PSMA probes described during the last years, this review aims to give an overview over the specific characteristics of those radiopharmaceuticals that have already found widespread clinical application. In addition, recently introduced concepts such as PSMA-tracers with increased plasma protein binding, are discussed.

Recent Advances in Prostate-Specific Membrane Antigen-Based Radiopharmaceuticals

BACKGROUND

Prostate cancer (PCa) is the most common sex-related malignancy with high mortality in men worldwide. Prostate-specific membrane antigen (PSMA) is overexpressed on the surface of most prostate tumor cells and considered a valuable target for both diagnosis and therapy of prostate cancer. A series of radiolabeled agents have been developed based on the featured PSMA ligands in the previous decade and have demonstrated promising outcomes in clinical research of primary and recurrent PCa. Furthermore, the inspiring response and safety of lutetium-177-PSMA-617 (177Lu-PSMA-617) radiotherapy represent the potential for expanded therapeutic options for metastatic castration-resistant PCa. Retrospective cohort studies have revealed that radiolabeled PSMA agents are the mainstays of the current success, especially in detecting prostate cancer with metastasis and biochemical recurrence.

OBJECTIVE

This review is intended to present a comprehensive overview of the current literature on PSMA ligand-based agents for both radionuclide imaging and therapeutic approaches, with a focus on those that have been clinically adopted.

CONCLUSION

PSMA-based diagnosis and therapy hold great promise for improving the clinical management of prostate cancer.

Prostate-specific markers to identify rare prostate cancer cells in liquid biopsies

Despite improvements in early detection and advances in treatment, patients with prostate cancer continue to die from their disease. Minimal residual disease after primary definitive treatment can lead to relapse and distant metastases, and increasing evidence suggests that circulating tumour cells (CTCs) and bone marrow-derived disseminated tumour cells (BM-DTCs) can offer clinically relevant biological insights into prostate cancer dissemination and metastasis. Using epithelial markers to accurately detect CTCs and BM-DTCs is associated with difficulties, and prostate-specific markers are needed for the detection of these cells using rare cell assays. Putative prostate-specific markers have been identified, and an optimized strategy for staining rare cancer cells from liquid biopsies using these markers is required. The ideal prostate-specific marker will be expressed on every CTC or BM-DTC throughout disease progression (giving high sensitivity) and will not be expressed on non-prostate-cancer cells in the sample (giving high specificity). Some markers might not be specific enough to the prostate to be used as individual markers of prostate cancer cells, whereas others could be truly prostate-specific and would make ideal markers for use in rare cell assays. The goal of future studies is to use sensitive and specific prostate markers to consistently and reliably identify rare cancer cells.

Imaging of Prostate-Specific Membrane Antigen with Small-Molecule PET Radiotracers: From the Bench to Advanced Clinical Applications

In recent years, small-molecule inhibitors of prostate-specific membrane antigen (PSMA) labeled with radionuclides that allow for positron emission tomography (PET) imaging have been extensively studied in many clinical contexts in men with prostate cancer (PCa). The high sensitivity and specificity of these agents for identifying sites of PCa has quickly led to their widespread adoption as a de facto clinical standard of care throughout much of the world. PSMA-targeted PET radiotracers have been particularly well-studied in preoperatively staging men with high-risk PCa, evaluating biochemical recurrence following definitive therapy, and guiding metastasis-directed therapy in patients suspected of having oligorecurrent/oligometastatic disease. Furthermore, the expression of PSMA on the tumor neovasculature of many nonprostate malignancies has enabled a burgeoning subfield concentrated on delineating the potential utility of PSMA-targeted PET agents for imaging other cancers. In this review, we highlight the preclinical development of key small molecules that are now being clinically utilized for PCa imaging, discuss the roles of PSMA-targeted agents in guiding patient management, and consider the role these compounds may play in imaging nonprostate cancers.

Imaging as a Personalized Biomarker for Prostate Cancer Risk Stratification

Biomarkers provide objective data to guide clinicians in disease management. Prostate-specific antigen serves as a biomarker for screening of prostate cancer but has come under scrutiny for detection of clinically indolent disease. Multiple imaging techniques demonstrate promising results for diagnosing, staging, and determining definitive management of prostate cancer. One such modality, multiparametric magnetic resonance imaging (mpMRI), detects more clinically significant disease while missing lower volume and clinically insignificant disease. It also provides valuable information regarding tumor characteristics such as location and extraprostatic extension to guide surgical planning. Information from mpMRI may also help patients avoid unnecessary biopsies in the future. It can also be incorporated into targeted biopsies as well as following patients on active surveillance. Other novel techniques have also been developed to detect metastatic disease with advantages over traditional computer tomography and magnetic resonance imaging, which primarily rely on defined size criteria. These new techniques take advantage of underlying biological changes in prostate cancer tissue to identify metastatic disease. The purpose of this review is to present literature on imaging as a personalized biomarker for prostate cancer risk stratification.

A Prospective Comparison of 18F-Sodium Fluoride PET/CT and PSMA-Targeted 18F-DCFBC PET/CT in Metastatic Prostate Cancer

The purpose of this study was to compare the diagnostic performance of 18F-DCFBC PET/CT, a first-generation 18F-labeled prostate-specific membrane antigen (PSMA)-targeted agent, and 18F-NaF PET/CT, a sensitive marker of osteoblastic activity, in a prospective cohort of patients with metastatic prostate cancer. Methods: Twenty-eight prostate cancer patients with metastatic disease on conventional imaging prospectively received up to 4 PET/CT scans. All patients completed baseline 18F-DCFBC PET/CT and 18F-NaF PET/CT scans, and 23 patients completed follow-up imaging, with a median follow-up interval of 5.7 mo (range, 4.2-12.6 mo). Lesion detection was compared across the 2 PET/CT agents at each time point. Detection and SUV characteristics of each PET/CT agent were compared with serum prostate-specific antigen (PSA) levels and treatment status at the time of baseline imaging using nonparametric statistical testing (Spearman correlation, Wilcoxon rank). Results: Twenty-six patients had metastatic disease detected on 18F-NaF or 18F-DCFBC at baseline, and 2 patients were negative on both scans. Three patients demonstrated soft tissue-only disease. Of 241 lesions detected at baseline, 56 were soft-tissue lesions identified by 18F-DCFBC only and 185 bone lesions detected on 18F-NaF or 18F-DCFBC. 18F-NaF detected significantly more bone lesions than 18F-DCFBC (P < 0.001). Correlation of PSA with patient-level SUV metrics was strong in 18F-DCFBC (ρ > 0.5, P < 0.01) and poor in 18F-NaF (ρ < 0.3, P > 0.1). When PSA levels were combined with treatment status, patients with below-median levels of PSA (<2 ng/mL) on androgen deprivation therapy (n = 11) demonstrated more lesions on 18F-NaF than 18F-DCFBC (P = 0.02). In PSA greater than 2 ng/mL, patients on androgen deprivation therapy (n = 8) showed equal to or more lesions on 18F-DCFBC than on 18F-NaF. Conclusion: The utility of PSMA-targeting imaging in metastatic prostate cancer appears to depend on patient disease course and treatment status. Compared with 18F-NaF PET/CT, 18F-DCFBC PET/CT detected significantly fewer bone lesions in the setting of early or metastatic castrate-sensitive disease on treatment. However, in advanced metastatic castrate-resistant prostate cancer, 18F-DCFBC PET/CT shows good concordance with NaF PET/CT.

Keeping up with the prostate-specific membrane antigens (PSMAs): an introduction to a new class of positron emission tomography (PET) imaging agents

Prostate-specific membrane antigen (PSMA) targeted positron emission tomography (PET) is an emerging prostate cancer imaging method, which has been reported to have a higher sensitivity and specificity than the currently approved PET imaging agents. Multiple PSMA ligands are being investigated around the world and applications range from primary tumor characterization, to local staging, biochemical recurrence, metastasis, and image-guided interventions. The most investigated PET tracers are labelled with 68-Gallium or 18-Fluoride and are discussed in this review. Additionally, 99mTc labeled PSMA agents for single photon emission computed tomography (SPECT) imaging are elucidated as an alternative method of PSMA image acquisition.

Follow-up of Lesions with Equivocal Radiotracer Uptake on PSMA-Targeted PET in Patients with Prostate Cancer: Predictive Values of the PSMA-RADS-3A and PSMA-RADS-3B Categories

Prostate-specific membrane antigen (PSMA)-targeted PET imaging has become commonly used in patients with prostate cancer (PCa). The PSMA reporting and data system version 1.0 (PSMA-RADS version 1.0) categorizes lesions on the basis of the likelihood of PCa involvement, with PSMA-RADS-3A (soft-tissue) and PSMA-RADS-3B (bone) lesions being indeterminate for the presence of disease. We retrospectively reviewed the imaging follow-up of such lesions to determine the rate at which they underwent changes suggestive of underlying PCa. Methods: PET/CT imaging with ¹⁸F-DCFPyL was performed in 110 patients with PCa, and lesions were categorized according to PSMA-RADS version 1.0. The study reported herein is a retrospective analysis of those patients. Fifty-six of 110 (50.9%) patients were determined to have indeterminate PSMA-RADS-3A or PSMA-RADS-3B lesions, and 22 of 56 (39.3%) patients had adequate follow-up to be included in the analysis (median follow-up time was 10 mo [range, 3-22 mo]). The SUV_max of the lesions was obtained, and the ratios of SUV_max of the lesions to SUV_mean of blood pool (SUV_max-lesion/SUV_{mean-bloodpool}) were calculated. Predetermined criteria were used to evaluate the PSMA-RADS-3A and PSMA-RADS-3B lesions on follow-up imaging to determine whether they demonstrated evidence of underlying malignancy. Results: A total of 46 lesions in 22 patients were considered indeterminate for PCa (i.e., PSMA-RADS-3A [32 lesions] or PSMA-RADS-3B [14 lesions]) and were evaluable on follow-up imaging. Twenty-seven of 46 (58.7%) lesions demonstrated changes suggesting they were true-positive for PCa. These lesions included 24 of 32 (75.0%) PSMA-RADS-3A lesions and 3 of 14 (21.4%) lesions categorized as PSMA-RADS-3B. The ranges of SUV_max and SUV_max-lesion/SUV_{mean-bloodpool} overlapped between those lesions demonstrating changes consistent with malignancy on follow-up imaging and those lesions that remained unchanged on follow-up. The presence of additional definitive sites of PCa (PSMA-RADS-4 and PSMA-RADS-5) increases the likelihood that indeterminate lesions will manifest as true-positive on follow-up imaging. Conclusion: PSMA-RADS-3A and PSMA-RADS-3B lesions are truly indeterminate in that proportions of findings in both categories demonstrate evidence of malignancy on follow-up imaging. Overall, PSMA-RADS-3A lesions are more likely than PSMA-RADS-3B lesions to represent sites of PCa, and this information should be considered when guiding patient therapy.

Role of PET imaging for biochemical recurrence following primary treatment for prostate cancer

Prostate cancer is one of the most common cancers in men worldwide, and primary prostate cancer is typically treated with surgery, radiation, androgen deprivation, or a combination of these therapeutic modalities. Despite technical advances, approximately 30% of men will experience biochemical recurrent within 10 years of definitive treatment. Upon detection of a rise in serum prostate specific antigen (PSA), there is great need to accurately stage these patients to help guide further therapy. As a result, there are considerable efforts underway to establish the role of positron emission tomography (PET) in the diagnostic algorithm of biochemically recurrent prostate cancer. This manuscript provides an overview of PET tracers used for the detection and localization of prostate cancer in the setting of biochemical recurrence with a focus on PET tracers that are currently being used in clinical practice in the United States.

Current and potential future role of PSMA-PET in patients with castration-resistant prostate cancer

PURPOSE

To review the current literature and discuss potential future roles of the novel positron emission tomography (PET) tracers targeting the prostate-specific membrane antigen (PSMA) in patients with castration-resistant prostate cancer (CRPC).

METHODS

A literature search on February 19th 2018 was conducted using the Medline database and www.clinicaltrials.gov . Additionally, illustrative cases of CRPC patients from our own institution who were restaged and treated based on PSMA-PET scan results are provided.

RESULTS

11 Studies met the inclusion criteria. PSMA-PET detected more metastatic lesions compared to conventional bone scan. Several patients were up-staged from non-metastatic CRPC (nmCRPC) to metastatic CRPC (mCRPC). Currently, no clear consensus exists regarding treatment response assessment in PSMA-PET scans for mCRPC patients undergoing treatment. Also, the role of PSMA-PET as a gatekeeper for systemic therapy or radioligands is currently undefined. PSMA-guided metastasis-directed radiotherapy may not only alleviate local symptoms but has the potential to defer systemic treatment in patients with oligoprogressive CRPC.

CONCLUSION

Compared to bone scan, PSMA-PET is more sensitive and specific to detect metastases but the therapeutic consequences of PSMA-PET results in the setting of CRPC remain unclear. Until future studies define the role of PSMA-PET in patients with CRPC, the current standard for imaging remains bone scan and computerized tomography.

Theranostics of prostate cancer: from molecular imaging to precision molecular radiotherapy targeting the prostate specific membrane antigen

Alterations at the molecular level are a hallmark of cancer. Prostate cancer is associated with the overexpression of prostate-specific membrane antigen (PSMA) in a majority of cases, predominantly in advanced tumors, increasing with the grade or Gleason's score. PSMA can be selectively targeted using radiolabeled PSMA ligands. These small molecules binding the PSMA can be radiolabeled with γ-emitters like ^99mTc and ¹¹¹In or positron emitters like ⁶⁸Ga and ¹⁸F for diagnosis as well as with their theranostic pairs such as ¹⁷⁷Lu (β-emitter) or ²²⁵Ac (α-emitter) for therapy. This review summarizes the theranostic role of PSMA ligands for molecular imaging and targeted molecular radiotherapy, moving towards precision oncology.