Concordance between Response Assessment Using Prostate-Specific Membrane Antigen PET and Serum Prostate-Specific Antigen Levels after Systemic Treatment in Patients with Metastatic Castration Resistant Prostate Cancer: A Systematic Review and Meta-Analysis

Correlation of [68Ga]Ga-PSMA PET/CT response and PSA decline in first-line enzalutamide for metastatic castration-resistant prostate cancer patients

PURPOSE

to assess the utility of response monitoring to enzalutamide by using [68Ga]Ga-PSMA PET in mCRPC patients treated with enzalutamide as first-line therapy.

METHODS

patients underwent [68Ga]Ga-PSMA PET less than 8 weeks before and 3 months after starting enzalutamide. On the basis of EAU/EANM criteria, patients were categorized as PSMA responders (PET-R) or PSMA non-responders (PET-NR), whilst, based on PSA, they were classified as biochemical responders (PSA-R) or non-responders (PSA-NR). Survival analysis was performed using the Cox regression hazard model and the Kaplan-Meier method.

RESULTS

69 patients were considered fully evaluable. We observed 47.8% of concordance between [68Ga]Ga-PSMA PET and PSA monitoring at 3 months after starting enzalutamide. For discordant cases, the PSA reduction has a weak impact on PFS and a significant impact on OS in PET-NR patients, whilst this change has no impact either for PFS and OS in PET-R ones.

CONCLUSIONS

[68Ga]Ga-PSMA PET could be a useful imaging tool for monitoring response to enzalutamide in mCRPC patients, being more informative than PSA in this setting, and possibly better guiding clinicians in therapeutic decisions.

Value of Whole-body Magnetic Resonance Imaging Using the MET-RADS-P Criteria for Assessing the Response to Intensified Androgen Deprivation Therapy in Metastatic Hormone-naïve and Castration-resistant Prostate Cancer

BACKGROUND AND OBJECTIVES

We assessed the agreement between prostate-specific antigen (PSA) and imaging responses using whole-body magnetic resonance imaging (wbMRI). Our aim was to explore the potential prognostic value of PSA and wbMRI responses in metastatic hormone-naïve prostate cancer (mHNPC) and castration-resistant PC (mCRPC).

METHODS

wbMRI was prospectively performed in 37 patients with mHNPC and 51 with mCRPC before and after 6-12 mo of androgen deprivation therapy and an androgen receptor pathway inhibitor (ARPI). Imaging responses were defined according to the Metastasis Reporting and Data System for PC (MET-RADS-P) criteria. A PSA response was defined as PSA ≤0.2 ng/ml in mHNPC and a ≥50% decrease from the pretreatment level in mCRPC. Agreement between PSA and wbMRI responses was assessed using Cohen's κ. The association between time to subsequent treatment and overall survival (OS) was analyzed using Cox regression analysis.

KEY FINDINGS AND LIMITATIONS

Agreement between PSA and wbMRI responses was fair in mHNPC (κ = 0.30) but none to slight in mCRPC (κ = 0.15). In mHNPC, patients with a PSA or wbMRI response were less likely to receive subsequent treatments; wbMRI progression was associated with a significantly higher risk of death (hazard ratio 8.59; p = 0.002). In mCRPC, two-thirds of patients with a PSA response showed progression on wbMRI; neither PSA nor wbMRI progression changed the likelihood of starting a subsequent treatment or the risk of death.

CONCLUSIONS AND CLINICAL IMPLICATIONS

In mHNPC, wbMRI progression was associated with a higher risk of needing subsequent treatment and shorter OS.

PATIENT SUMMARY

We evaluated the agreement between routine PSA (prostate-specific antigen) test results and whole-body MRI (magnetic resonance imaging) scans for assessing the response of metastatic prostate cancer to treatment. There was disagreement between the PSA and MRI results, mainly for patients with cancer that was resistant to hormone-based treatment. Combining PSA with whole-body MRI might provide a more accurate picture of the response of advanced prostate cancer to treatment.

A prospective study on the early evaluation of response to androgen receptor-targeted agents with 11C-Choline, 68Ga-PSMA, and 18F-FACBC PET in metastatic castration-resistant prostate cancer: a single-center experience

BACKGROUND

The early identification of responsive and resistant patients to androgen receptor-targeting agents (ARTA) in metastatic castration-resistant prostate cancer (mCRPC) is not completely possible with prostate-specific antigen (PSA) assessment and conventional imaging. Considering its ability to determine metabolic activity of lesions, positron emission tomography (PET) assessment might be a promising tool.

PATIENTS AND METHODS

We carried out a monocentric prospective study in patients with mCRPC treated with ARTA to evaluate the role of different PET radiotracers: 49 patients were randomized to receive 11C-Choline, Fluorine 18 fluciclovine (anti-1-amino-3-18F-fluorocyclobutane-1-carboxylic acid - FACBC) (18F-FACBC), or Gallium-68-prostate-specific-membrane-antigen (68Ga-PSMA) PET, one scan before therapy and one 2 months later. The primary aim was to investigate the performance of three novel PET radiotracers for the early evaluation of response to ARTA in metastatic CRPC patients; the outcome evaluated was biochemical response (PSA reduction ≥50%). The secondary aim was to investigate the prognostic role of several semiquantitative PET parameters and their variations with the different radiotracers in terms of biochemical progression-free survival (bPFS) and overall survival (OS). The study was promoted by the Italian Department of Health (code RF-2016-02364809).

RESULTS

Regarding the primary endpoint, at log-rank test a statistically significant correlation was found between metabolic tumor volume (MTV) (P = 0.018) and total lesion activity (TLA) (P = 0.025) percentage variation among the two scans with 68Ga-PSMA PET and biochemical response. As for the secondary endpoints, significant correlations with bPFS were found for 68Ga-PSMA total MTV and TLA at the first scan (P = 0.001 and P = 0.025, respectively), and MTV percentage variation (P = 0.031). For OS, statistically significant correlations were found for different 68Ga-PSMA and 18F-FACBC parameters and for major maximum standardized uptake value at the first 11C-Choline PET scan.

CONCLUSIONS

Our study highlighted that 11C-Choline, 68Ga-PSMA, and 18F-FACBC semiquantitative PET parameters and their variations present a prognostic value in terms of OS and bPFS, and MTV and TLA variations with 68Ga-PSMA PET a correlation with biochemical response, which could help to assess the response to ARTA.

PSMA-Targeted Radiopharmaceuticals for Prostate Cancer Diagnosis and Therapy

ABSTRACT

Prostate cancer (PCa) is the most common noncutaneous malignancy in men. Until recent years, accurate imaging of men with newly diagnosed PCa, or recurrent or low-volume metastatic disease, was limited. Further, therapeutic options for men with advanced, metastatic, castration-resistant disease were increasingly limited as a result of increasing numbers of systemic therapies being combined in the upfront metastatic setting. The advent of urea-based, small-molecule inhibitors of prostate-specific membrane antigen (PSMA) has partially addressed those shortcomings in diagnosis and therapy of PCa. On the diagnostic side, there are multiple pivotal phase III trials with several different agents having demonstrated utility in the initial staging setting, with generally modest sensitivity but very high specificity for determining otherwise-occult pelvic nodal involvement. That latter statistic drives the utility of the scan by allowing imaging interpreters to read with very high sensitivity while maintaining a robust specificity. Other pivotal phase III trials have demonstrated high detection efficiency in patients with biochemical failure, with high positive predictive value at the lesion level, opening up possible new avenues of therapy such as metastasis-directed therapy. Beyond the diagnostic aspects of PSMA-targeted radiotracers, the same urea-based chemical scaffolds can be altered to deliver therapeutic isotopes to PCa cells that express PSMA. To date, one such agent, when combined with best standard-of-care therapy, has demonstrated an ability to improve overall survival, progression-free survival, and freedom from skeletal events relative to best standard-of-care therapy alone in men with metastatic, castration-resistant PCa who are post chemotherapy. Within the current milieu, there are a number of important future directions including the use of artificial intelligence to better leverage diagnostic findings, further medicinal chemistry refinements to the urea-based structure that may allow improved tumor targeting and decreased toxicities, and the incorporation of new radionuclides that may better balance efficacy with toxicities than those nuclides that are available.

Theranostics revolution in prostate cancer: Basics, clinical applications, open issues and future perspectives

In the last years, theranostics has expanded the therapeutic options available for prostate cancer patients. In this review, we explore this dynamic field and its potential to revolutionize precision medicine for prostate cancer. We delve into the foundational principles, clinical applications, and emerging opportunities, emphasizing the potential synergy between radioligand therapy and other systemic treatments. Additionally, we address the ongoing challenges, including optimizing patient selection, assessing treatment responses, and determining the role of theranostics within the broader landscape of prostate cancer treatment.

The Current Landscape of Prostate-Specific Membrane Antigen (PSMA) Imaging Biomarkers for Aggressive Prostate Cancer

The review examines the vital role of prostate-specific membrane antigen (PSMA) positron emission tomography/computed tomography (PET/CT) in the diagnosis, staging, and treatment of prostate cancer (PCa). It focuses on the superior diagnostic abilities of PSMA PET/CT for identifying both nodal and distant PCa, and its potential as a prognostic indicator for biochemical recurrence and overall survival. Additionally, we focused on the variability of PSMA's expression and its impact on personalised treatment, particularly the use of [177Lu] Lu-PSMA-617 radioligand therapy. This review emphasises the essential role of PSMA PET/CT in enhancing treatment approaches, improving patient outcomes, and reducing unnecessary interventions, positioning it as a key element in personalised PCa management.

Applications of Artificial Intelligence in PSMA PET/CT for Prostate Cancer Imaging

Prostate-specific membrane antigen (PSMA) positron emission tomography/computed tomography (PET/CT) has emerged as an important imaging technique for prostate cancer. The use of PSMA PET/CT is rapidly increasing, while the number of nuclear medicine physicians and radiologists to interpret these scans is limited. Additionally, there is variability in interpretation among readers. Artificial intelligence techniques, including traditional machine learning and deep learning algorithms, are being used to address these challenges and provide additional insights from the images. The aim of this scoping review was to summarize the available research on the development and applications of AI in PSMA PET/CT for prostate cancer imaging. A systematic literature search was performed in PubMed, Embase and Cinahl according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. A total of 26 publications were included in the synthesis. The included studies focus on different aspects of artificial intelligence in PSMA PET/CT, including detection of primary tumor, local recurrence and metastatic lesions, lesion classification, tumor quantification and prediction/prognostication. Several studies show similar performances of artificial intelligence algorithms compared to human interpretation. Few artificial intelligence tools are approved for use in clinical practice. Major limitations include the lack of external validation and prospective design. Demonstrating the clinical impact and utility of artificial intelligence tools is crucial for their adoption in healthcare settings. To take the next step towards a clinically valuable artificial intelligence tool that provides quantitative data, independent validation studies are needed across institutions and equipment to ensure robustness.

European Association of Nuclear Medicine Focus 5: Consensus on Molecular Imaging and Theranostics in Prostate Cancer

BACKGROUND

In prostate cancer (PCa), questions remain on indications for prostate-specific membrane antigen (PSMA) positron emission tomography (PET) imaging and PSMA radioligand therapy, integration of advanced imaging in nomogram-based decision-making, dosimetry, and development of new theranostic applications.

OBJECTIVE

We aimed to critically review developments in molecular hybrid imaging and systemic radioligand therapy, to reach a multidisciplinary consensus on the current state of the art in PCa.

DESIGN, SETTING, AND PARTICIPANTS

The results of a systematic literature search informed a two-round Delphi process with a panel of 28 PCa experts in medical or radiation oncology, urology, radiology, medical physics, and nuclear medicine. The results were discussed and ratified in a consensus meeting.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

Forty-eight statements were scored on a Likert agreement scale and six as ranking options. Agreement statements were analysed using the RAND appropriateness method. Ranking statements were analysed using weighted summed scores.

RESULTS AND LIMITATIONS

After two Delphi rounds, there was consensus on 42/48 (87.5%) of the statements. The expert panel recommends PSMA PET to be used for staging the majority of patients with unfavourable intermediate and high risk, and for restaging of suspected recurrent PCa. There was consensus that oligometastatic disease should be defined as up to five metastases, even using advanced imaging modalities. The group agreed that [177Lu]Lu-PSMA should not be administered only after progression to cabazitaxel and that [223Ra]RaCl2 remains a valid therapeutic option in bone-only metastatic castration-resistant PCa. Uncertainty remains on various topics, including the need for concordant findings on both [18F]FDG and PSMA PET prior to [177Lu]Lu-PSMA therapy.

CONCLUSIONS

There was a high proportion of agreement among a panel of experts on the use of molecular imaging and theranostics in PCa. Although consensus statements cannot replace high-certainty evidence, these can aid in the interpretation and dissemination of best practice from centres of excellence to the wider clinical community.

PATIENT SUMMARY

There are situations when dealing with prostate cancer (PCa) where both the doctors who diagnose and track the disease development and response to treatment, and those who give treatments are unsure about what the best course of action is. Examples include what methods they should use to obtain images of the cancer and what to do when the cancer has returned or spread. We reviewed published research studies and provided a summary to a panel of experts in imaging and treating PCa. We also used the research summary to develop a questionnaire whereby we asked the experts to state whether or not they agreed with a list of statements. We used these results to provide guidance to other health care professionals on how best to image men with PCa and what treatments to give, when, and in what order, based on the information the images provide.

PSMA PET/CT for Response Assessment and Overall Survival Prediction in Patients with Metastatic Castration-Resistant Prostate Cancer Treated with Androgen Receptor Pathway Inhibitors

We aimed to evaluate the role of prostate-specific membrane antigen (PSMA) PET/CT for response assessment and outcome prediction in patients with metastatic castration-resistant prostate cancer (mCRPC) treated with androgen receptor pathway inhibitors (ARPIs), including abiraterone acetate or enzalutamide. Methods: We retrospectively analyzed 30 ARPI-treated mCRPC patients who underwent 68Ga-PSMA-11 PET/CT within 8 wk before (baseline) and 12 ± 4 wk after treatment initiation. Total PSMA tumor volume was calculated using the fixed threshold method (SUV ≥ 3). Patients were categorized as PSMA responders (PSMA-Rs) or PSMA nonresponders (PSMA-NRs) on the basis of both European Association of Urology/European Association of Nuclear Medicine (EAU/EANM) criteria and Response Evaluation Criteria in PSMA PET/CT (RECIP) 1.0. PSMA-R included patients with a complete response, a partial response, or stable disease, and PSMA-NR included those with progressive disease. On the basis of prostate-specific antigen (PSA), patients were classified as biochemical responders if PSA decreased by at least 50% and as nonresponders if it did not. The Φ-coefficient was used to evaluate the correlation of PSMA- and PSA-based responses. Survival analysis was performed using the Cox regression hazard model and the Kaplan-Meier method. Predictive accuracy was tested for both response criteria. Results: On the basis of PSMA PET/CT, 13 (43%) patients were PSMA-NR according to the EAU/EANM criteria and 11 (37%) patients were PSMA-NR according to RECIP 1.0. Significant correlations were observed between PSMA- and PSA-based responses for both criteria (Φ = 0.79 and 0.66, respectively). After a median follow-up of 25 mo (interquartile range, 21-43 mo), the median overall survival was significantly longer for PSMA-R than PSMA-NR (54 vs. 22 mo) for both the EAU/EANM criteria and RECIP 1.0, with hazard ratios of 6.9 (95% CI, 1.9-26; P = 0.004) and 5.6 (95% CI, 1.69-18.26, P = 0.005), respectively. No significant difference in predictive accuracy was found between the 2 criteria (C-index, 0.79 vs. 0.76, respectively, P = 0.54). Flare phenomena at the second PSMA PET study were not observed in our cohort. Conclusion: Our results demonstrate that PSMA PET/CT is a valuable imaging biomarker for response assessment and overall survival prediction when performed at 3 mo after ARPI treatment initiation in mCRPC patients. Both proposed PSMA response criteria (EAU/EANM and RECIP 1.0) seem to perform equally well. No PSMA flare was observed. Prospective validation of these findings is strongly needed.

The significance of metabolic response to neoadjuvant androgen deprivation therapy detected with [68Ga]Ga-PSMA-11-PET/CT in high-risk prostate cancer patients treated with definitive radiotherapy

PURPOSE

We examined the prognostic significance of early changes in primary tumor SUV measured with Gallium-68-labeled prostate-specific membrane antigen positron emission tomography ([68Ga]Ga-PSMA-11-PET/CT) and serum PSA values after neoadjuvant androgen deprivation treatment (nADT) in high-risk prostate cancer (PCa) patients treated with definitive radiotherapy (RT).

METHODS

The clinical data and SUV parameters of 71 PCa patients were reviewed retrospectively. The serum PSA and primary tumor SUV values were calculated before and after the start of ADT. Using univariable and multivariable analyses, the prognostic factors predicting biochemical disease free survival (bDFS) and prostate cancer specific survival (PCSS) were investigated. In addition, logistic regression analysis was used to identify predictors of biochemical failure (BF).

RESULTS

All but one patient responded with a 98.8% reduction in serum PSA (21.8 ng/mL vs. 0.3 ng/mL; p < 0.001), and 64 patients (91.1%) had a median 66.6% decrease in primary tumor SUV after ADT (13.2 vs. 4.8, p < 0.001). The primary tumor SUV response rate was significantly higher in patients with Gleason score (GS) of 7 than in patients with GS > 7 (59.5% vs. 40.5%; p = 0.04), and it was significantly lower in patients with inadequate treatment response than in those with complete (CR) or partial response (PR) (1.1% vs. 66.1%; p < 0.001). There was a strong and significant correlation (Spearman = 0.41, p < 0.001) and a high concordance (91.5%) between PSA response and SUV response after ADT. With a median follow-up time of 76.1 months, the 5-year bDFS and PCSS rates were 77.2% and 92.2%, respectively. Nineteen patients (26.7%) patients had recurrence at a median of 44.6 months after the completion of RT. In multivariate analysis, lymph node metastasis, GS greater than 7, and SD/PD after nADT were independent predictors of worse bDFS. However, no significant factor for PCSS was identified. In the multivariable logistic regression analysis, advanced age, GS of  > 7 disease, lymph node metastasis, and SD or PD after nADT were independent predictors of BF.

CONCLUSION

These results imply that the metabolic response measured with [68Ga]Ga-PSMA-11-PET/CT after nADT could be used to predict progression in high-risk PCa patients treated with definitive RT.

Diagnostic Performance of 68Ga-PSMA-11 Positron Emission Tomography/Computed Tomography to Monitor Treatment Response in Patients with Metastatic Prostate Cancer: The Concordance Between Biochemical Response and Prostate-specific Membrane Antigen Results

BACKGROUND

Treatment response is traditionally monitored using prostate-specific antigen (PSA) and conventional imaging in patients with metastatic prostate cancer (mPCa).

OBJECTIVE

To assess the diagnostic performance of prostate-specific membrane antigen (PSMA) positron emission tomography (PET)/computed tomography (CT) when monitoring mPCa patients receiving systemic treatment and also to investigate the concordance between PSMA PET response according to the PSMA PET progression (PPP) criteria and biochemical response.

DESIGN, SETTING, AND PARTICIPANTS

A total of 96 patients with 68Ga-PSMA-11 PET/CT-detected mPCa at baseline PSMA PET/CT (bPSMA) who underwent at least one follow-up scan after receiving systemic treatment were included in the study. PSA levels at bPSMA and follow-up PSMA PET (fPSMA) scans were recorded. The PPP criteria were used to define PSMA progression. Biochemical progression was defined as ≥25% increase in PSA. PSMA PET and PSA responses were dichotomized into progressive disease (PD) versus non-PD, and the concordance between PSA and PSMA responses was evaluated.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

The concordance between PSA and PSMA PET responses was presented using frequencies, percentages, and Cohen's kappa test.

RESULTS AND LIMITATIONS

A total of 345 serial PSMA PET/CT (96 bPSMA and 249 fPSMA) scans were evaluated. The positivity rates of PSMA PET scans for PSA levels of <0.01, 0.01-0.2, 0.2-4, and >4 ng/ml were 55.6%, 75.0%, 100%, and 98.8%, respectively. PSA and PSMA responses showed moderate-to-high concordance (Cohen's κ = 0.623, p < 0.001). PSA-PSMA discordance was detected in 39 scans (17%). The most common cause of discordance was the discordant results between different metastatic lesions (16/28, 57.1%) in patients with PPP without PSA progression and local progression in prostate (n = 7/11, 63.6%) in patients with PSA progression without PPP.

CONCLUSIONS

PSMA PET/CT showed very high detection rates of malignant lesions even at very low PSA values and showed significant concordance with PSA response when monitoring treatment response in patients receiving systemic treatment for mPCa.

PATIENT SUMMARY

This study describes that prostate-specific membrane antigen positron emission tomography (PSMA PET), a new sensitive imaging tool, can detect malignant lesions even at very low prostate-specific antigen values when monitoring metastatic prostate cancer. The PSMA PET response and biochemical response showed significant concordance, and the reason for discordant results seems to be the different responses of metastatic lesions and prostatic lesions to systemic treatment.

Diffusion-Weighted MRI for Treatment Response Assessment in Osteoblastic Metastases-A Repeatability Study

The apparent diffusion coefficient (ADC) is a candidate marker of treatment response in osteoblastic metastases that are not evaluable by morphologic imaging. However, it is unclear whether the ADC meets the basic requirement for reliable treatment response evaluation, namely a low variance of repeated measurements in relation to the differences found between viable and nonviable metastases. The present study addresses this question by analyzing repeated in vivo ADCmedian measurements of 65 osteoblastic metastases in nine patients, as well as phantom measurements. PSMA-PET served as a surrogate for bone metastasis viability. Measures quantifying repeatability were calculated and differences in mean ADC values according to PSMA-PET status were examined. The relative repeatability coefficient %RC of ADCmedian measurements was 5.8% and 12.9% for phantom and in vivo measurements, respectively. ADCmedian values of bone metastases ranged from 595×10-6mm2/s to 2090×10-6mm2/s with an average of 63% higher values in nonviable metastases compared with viable metastases (p < 0.001). ADC shows a small repeatability coefficient in relation to the difference in ADC values between viable and nonviable metastases. Therefore, ADC measurements fulfill the technical prerequisite for reliable treatment response evaluation in osteoblastic metastases.

Prostate-specific Membrane Antigen Positron Emission Tomography as a Biomarker to Assess Treatment Response in Patients with Advanced Prostate Cancer

CONTEXT

Prostate-specific membrane antigen (PSMA)-targeted positron emission tomography (PET) has superior accuracy for detection of metastatic lesions in patients with prostate cancer (PC). Although PSMA PET has a prominent role in primary and secondary imaging of PC, data on its role in assessing treatment response in advanced PC are limited.

OBJECTIVE

To review current data in the literature regarding the impact of antiandrogen therapy on PSMA expression of metastatic sites and the role of serial (baseline and at least 1 follow-up scan) PSMA PET to assess treatment response in patients with metastatic PC.

EVIDENCE ACQUISITION

A comprehensive literature search in the PubMed database was performed using the terms "PSMA expression prostate", "PSMA regulation", "PSMA PET response assessment", and "serial PSMA PET".

EVIDENCE SYNTHESIS

Serial PSMA PET studies (baseline and at least 1 follow-up scan) provide valuable data regarding PSMA expression changes after systemic treatment in patients with metastatic PC. PSMA PET-detected flare and upregulation of PSMA expression following hormonal intervention seem to be early events resolving after 3 mo of treatment. PSMA PET imaging is essential in selecting patients for ¹⁷⁷Lu-PSMA radioligand therapy (RLT). Growing evidence favors its use in assessing treatment responses after RLT. Preliminary evidence indicates the value of PSMA PET for assessment of the treatment response in patients receiving systemic treatment other than RLT for metastatic PC.

CONCLUSIONS

PSMA flare following antiandrogen therapy seems to be an early event and thus PET scans should be performed no earlier than 3 mo after the start of treatment. PSMA PET has a promising role in tailoring treatment according to the specific needs of individual patients and assessing responses following systemic treatment in patients with advanced PC.

PATIENT SUMMARY

This review describes how a sensitive imaging method can be used to assess the tumor response to treatment for metastatic prostate cancer.

Evaluation of Tumor Burden Response to Single-cycle of Lu-177 PSMA Treatment with Whole Body Scintigraphic Planar Images in Prostate Cancer Patients

The aim of this study; evaluation of treatment response and survival with post-therapy images in patients who received one cycle of Lu-177 PSMA I&T treatment.

The role of PSMA radioligands in the diagnosis and treatment of prostate carcinoma

Prostate cancer (PC) is the most common tumor in men in the West and the fifth leading cause of cancer-related death. The use of PSMA radioligands has represented an important advance both in its diagnosis, through PET molecular imaging, and in its treatment in advanced stages of the disease. This article reviews the contribution of PET studies with PSMA radioligands in initial staging, in tumor detection in biochemical recurrence (elevation of PSA) after treatment with curative intent, and in the more advanced stages of the disease (castration resistant PC or CRPC). The contribution of PSMA radioligand therapy (PSMA-RLT) in CRPC patients who progress to standard therapy is also analyzed.

Bone Metastases Are Measurable: The Role of Whole-Body MRI and Positron Emission Tomography

Metastatic tumor deposits in bone marrow elicit differential bone responses that vary with the type of malignancy. This results in either sclerotic, lytic, or mixed bone lesions, which can change in morphology due to treatment effects and/or secondary bone remodeling. Hence, morphological imaging is regarded unsuitable for response assessment of bone metastases and in the current Response Evaluation Criteria In Solid Tumors 1.1 (RECIST1.1) guideline bone metastases are deemed unmeasurable. Nevertheless, the advent of functional and molecular imaging modalities such as whole-body magnetic resonance imaging (WB-MRI) and positron emission tomography (PET) has improved the ability for follow-up of bone metastases, regardless of their morphology. Both these modalities not only have improved sensitivity for visual detection of bone lesions, but also allow for objective measurements of bone lesion characteristics. WB-MRI provides a global assessment of skeletal metastases and for a one-step "all-organ" approach of metastatic disease. Novel MRI techniques include diffusion-weighted imaging (DWI) targeting highly cellular lesions, dynamic contrast-enhanced MRI (DCE-MRI) for quantitative assessment of bone lesion vascularization, and multiparametric MRI (mpMRI) combining anatomical and functional sequences. Recommendations for a homogenization of MRI image acquisitions and generalizable response criteria have been developed. For PET, many metabolic and molecular radiotracers are available, some targeting tumor characteristics not confined to cancer type (e.g. 18F-FDG) while other targeted radiotracers target specific molecular characteristics, such as prostate specific membrane antigen (PSMA) ligands for prostate cancer. Supporting data on quantitative PET analysis regarding repeatability, reproducibility, and harmonization of PET/CT system performance is available. Bone metastases detected on PET and MRI can be quantitatively assessed using validated methodologies, both on a whole-body and individual lesion basis. Both have the advantage of covering not only bone lesions but visceral and nodal lesions as well. Hybrid imaging, combining PET with MRI, may provide complementary parameters on the morphologic, functional, metabolic and molecular level of bone metastases in one examination. For clinical implementation of measuring bone metastases in response assessment using WB-MRI and PET, current RECIST1.1 guidelines need to be adapted. This review summarizes available data and insights into imaging of bone metastases using MRI and PET.

Diagnostic performance of deep learning models for detecting bone metastasis on whole-body bone scan in prostate cancer

PURPOSE

We evaluated the performance of deep learning classifiers for bone scans of prostate cancer patients.

METHODS

A total of 9113 consecutive bone scans (5342 prostate cancer patients) were initially evaluated. Bone scans were labeled as positive/negative for bone metastasis using clinical reports and image review for ground truth diagnosis. Two different 2D convolutional neural network (CNN) architectures were proposed: (1) whole body-based (WB) and (2) tandem architectures integrating whole body and local patches, here named as "global-local unified emphasis" (GLUE). Both models were trained using abundant (72%:8%:20% for training:validation:test sets) and limited training data (10%:40%:50%). The allocation of test sets was rotated across all images: therefore, fivefold and twofold cross-validation test results were available for abundant and limited settings, respectively.

RESULTS

A total of 2991 positive and 6142 negative bone scans were used as input. For the abundant training setting, the receiver operating characteristics curves of both the GLUE and WB models indicated excellent diagnostic ability in terms of the area under the curve (GLUE: 0.936-0.955, WB: 0.933-0.957, P > 0.05 in four of the fivefold tests). The overall accuracies of the GLUE and WB models were 0.900 and 0.889, respectively. With the limited training setting, the GLUE models showed significantly higher AUCs than the WB models (0.894-0.908 vs. 0.870-0.877, P < 0.0001).

CONCLUSION

Our 2D-CNN models accurately classified bone scans of prostate cancer patients. While both showed excellent performance with the abundant dataset, the GLUE model showed higher performance than the WB model in the limited data setting.

Lutetium-177 Labelled PSMA Targeted Therapy in Advanced Prostate Cancer: Current Status and Future Perspectives

Patients suffering from metastatic castration-resistant prostate cancer (mCRPC) have a poor prognosis. As a further treatment option 177Lutetium (Lu) prostate-specific membrane antigen (PSMA) radioligand therapy gained a significant interest of many investigators. Several publications showed great response and prolonged survival with limited adverse events. However, to this point, it still remains unclear which patients benefit the most from 177Lu-PSMA therapy, and how to improve the treatment regimen to achieve best outcome while minimizing potential adverse events. The efficacy for mCRPC patients is a given fact, and with the newly published results of the VISION trial its approval is only a matter of time. Recently, investigators started to focus on treating prostate cancer patients in earlier disease stages and in combination with other compounds. This review gives a brief overview of the current state and the future perspectives of 177Lu labelled PSMA radioligand therapy.

PSMA Expression Predicts Early Biochemical Response in Patients with Metastatic Castration-Resistant Prostate Cancer under 177Lu-PSMA-617 Radioligand Therapy

Simple Summary

Prostate-specific membrane antigen (PSMA) is a promising target for both imaging and radioligand therapies (RLT) for men with prostate cancer. However, not all patients respond to RLT and some even progress early in the treatment course. We aimed to identify parameters to forecast which patients will achieve therapy response prior to commencing RLT. Therefore, we tested whether the tumor volume, the level of PSMA expression or a combination of both in metastases derived from PSMA-targeted molecular imaging prior to RLT can inform the treating physician whether a patient will respond to RLT. Compared to tumor volume, the level of PSMA-expression can better identify patients responding to RLT early in the treatment course.

Abstract

¹⁷⁷Lu-Prostate-specific membrane antigen (PSMA)-radioligand therapy (RLT) is a promising treatment option in patients with metastatic castration-resistant prostate cancer (mCRPC). We aimed to determine the predictive value of pretherapeutic PSMA-ligand positron emission tomography (PET) and established clinical parameters for early biochemical response after two cycles of RLT. In total, 71 mCRPC patients who had undergone PET/computed tomography (CT) with ⁶⁸Ga-PSMA-11 prior to two cycles of ¹⁷⁷Lu-PSMA-617 RLT were included. Malignant lesions on pretherapeutic PET/CTs were manually segmented and average maximum PSMA expression (maximum standardized uptake values, SUV_max), whole-body PSMA-tumor volume (TV), and whole-body total lesion (TL)-PSMA were calculated. We then tested the predictive performance of these parameters for early biochemical response (defined as prostate-sepcific antigen (PSA) decrease of ≥50% according to PCWG2) after two cycles of RLT, relative to established clinical parameters. Early PSA response was observed in 34/71 patients. PSA change after two cycles of RLT correlated with pretherapeutic SUV_max (r = −0.49; p < 0.001), but not with PSMA-TV (r = 0.02; p = 0.89) or TL-PSMA (r = −0.15; p = 0.22). A cut-off of 19.8 for SUV_max and 75.5 years for age was defined by receiver operating characteristics and revealed a significant outcome difference for early biochemical response between patients with adversely low vs. high PSMA expression and low vs. high age (p < 0.001). Multivariate analysis identified SUV_max (HR, 7.94, p = 0.001) and age (HR, 8.05, p = 0.002) as independent predictors for PSA response early in the treatment course. Thus, high age and high PSMA expression in patients scheduled for RLT identify patients with early biochemical response. This study provides a rationale for further prospective studies exploring PET-guided treatment intensification in selected patients.