Response assessment using [68 Ga]Ga-PSMA ligand PET in patients undergoing systemic therapy for metastatic castration-resistant prostate cancer

Prognostic Significance of Baseline Clinical and [68Ga]Ga-PSMA PET Derived Parameters on Biochemical Response, Overall Survival, and PSA Progression-Free Survival in Metastatic Castration-Resistant Prostate Cancer (mCRPC) Patients Undergoing [177Lu]Lu-PSMA Therapy

BACKGROUND

In this study, we sought to identify the clinical baseline characteristics and pre-therapy 68Ga-PSMA PET derived parameters that can have impact on PSA (biochemical) response, OS and PSA PFS in patients with metastatic castration-resistant prostate cancer (mCRPC) who undergo RLT with [177Lu]Lu-PSMA-617.

METHODS

Various pre-treatment clinical and PSMA PET derived parameters were gathered and computed. We used PSA response as the criteria for more than a 50% decrease in PSA level, and OS and PSA PFS as endpoints. We assessed the collected parameters in relation to PSA response. Additionally, we employed univariable Cox regression and Kaplan-Meier analysis with log rank to evaluate the influence of the parameters on OS and PFS.

RESULTS

A total of 125 mCRPC patients were included in this study. The median age was 68 years (range: 49-89). Among the cases, 77 patients (62%) showed PSARS, while 48 patients (38%) did not show PSA response. The median OS was 14 months (range: 1-60), and the median PSA-PFS was 10 months (range: 1-56). Age, prior history of chemotherapy, and SUVmax had a significant impact on PSA response (p<0.05). PSA response, RBC count, hemoglobin, hematocrit, neutrophil to lymphocyte ratio (NLR), alkaline phosphatase (ALP), number of metastases, wbPSMA-TV, and wbTL-PSMA significantly affected OS. GS, platelet count, NLR, and number of metastases were found to have a significant impact on PSA PFS.

CONCLUSION

We have identified several baseline clinical and PSMA PET derived parameters that can serve as prognostic factors for predicting PSA response, OS, and PSA PFS after RLT. Based on the findings, we believe that these clinical baseline characteristics can assist nuclear medicine specialists in identifying RLT responders who have long-term survival and PFS.

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.

Real-world Outcomes and Predictive Biomarkers for 177Lutetium Prostate-specific Membrane Antigen Ligand Treatment in Metastatic Castration-resistant Prostate Cancer: A European Association of Urology Young Academic Urologists Prostate Cancer Working Group Multi-institutional Observational Study

BACKGROUND

The European Association of Urology guidelines include the lutetium-177 (177Lu) PSMA-617 prostate-specific membrane antigen (PSMA) ligand as a therapy option for metastatic castration-resistant prostate cancer (mCRPC). A major challenge in clinical practice is to pursue a personalized treatment approach based on robust predictive biomarkers.

OBJECTIVE

To assess the performance of 177Lu PSMA in real-world practice and to elaborate clinical biomarkers for evaluating treatment responses.

DESIGN, SETTING, AND PARTICIPANTS

We conducted a retrospective observational study including 233 patients with mCRPC treated with 177Lu PSMA in eight high-volume European centers.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

Baseline characteristics and clinical parameters during and after 177Lu PSMA treatment were documented. Correlations to treatment response were analyzed using χ2 and log-rank tests, with differences between groups with and without disease progression calculated using a Mann-Whitney U test. Univariate and multivariate-adjusted hazard ratios (HRs) were measured using Cox proportional hazards models.

RESULTS AND LIMITATIONS

A prostate-specific antigen (PSA) decrease of ≥30% was observed in 41.7%, 63.5%, and 77.8% of patients after the first, second, and third treatment cycle, respectively. Restaging performed via PSMA positron emission tomography-computed tomography revealed that 33.7% of patients had an imaging-based response, including two patients with a complete response, while 13.4% had stable disease. The median time to progression was 5 mo and the median time until the start of a consecutive antineoplastic therapy was 8.5 mo. Of importance, a PSA decrease ≥30% after the first two cycles of 177Lu PSMA (1 cycle: p = 0.0003; 2 cycles: p = 0.004), absolute PSA after the first three cycles (1 cycle: p = 0.011; 2 cycles: p = 0.0005; 3 cycles: p = 0.002), and a PSA doubling time >6 mo (p = 0.009) were significantly correlated to treatment response. Furthermore, gamma-glutamyl transferase ≤31 U/L at the start of 177Lu PSMA therapy was correlated with 1.5 times higher risk of progression for patients without but not with visceral metastases (p = 0.046).

CONCLUSIONS

177Lu PSMA is an effective treatment option in mCRPC in the real-world setting. A PSA decrease ≥30% after the first two cycles is an early marker of response that can be easily implemented in clinical practice.

PATIENT SUMMARY

177Lu PSMA is a radioactive agent approved for treatment of advanced prostate cancer. We reviewed its use outside of clinical trials for patients treated at eight European centers. We found that 177Lu PSMA is an effective treatment option in real-world practice. A PSA (prostate-specific antigen) decrease of ≥30% after the first two therapy cycles is an early indicator of response to treatment and can be used in personalizing treatments for patients.

Impact of Circulating Tumor Cell-Expressed Prostate-Specific Membrane Antigen and Prostate-Specific Antigen Transcripts in Different Stages of Prostate Cancer

PURPOSE

Prostate-specific membrane antigen (PSMA)-based images, which visually quantify PSMA expression, are used to determine prostate cancer micrometastases. This study evaluated whether a circulating tumor cell (CTC)-based transcript platform, including PSMA mRNA, could help identify potential prognostic markers in prostate cancer.

EXPERIMENTAL DESIGN

We prospectively enrolled 21 healthy individuals and 247 patients with prostate cancer [localized prostate cancer (LPCa), n = 94; metastatic hormone-sensitive prostate cancer (mHSPC), n = 44; and metastatic castration-resistant prostate cancer (mCRPC), n = 109]. The mRNA expression of six transcripts [PSMA, prostate-specific antigen (PSA), AR, AR-V7, EpCAM, and KRT 19] from CTCs was measured, and their relationship with biochemical recurrence (BCR) in LPCa and mCRPC progression-free survival (PFS) rate in mHSPC was assessed. PSA-PFS and radiological-PFS were also calculated to identify potential biomarkers for predicting androgen receptor signaling inhibitor (ARSI) and taxane-based chemotherapy resistance in mCRPC.

RESULTS

CTC detection rates were 75.5%, 95.3%, and 98.0% for LPCa, mHSPC, and mCRPC, respectively. In LPCa, PSMA [hazard ratio (HR), 3.35; P = 0.028) and PSA mRNA (HR, 1.42; P = 0.047] expressions were associated with BCR. Patients with mHSPC with high PSMA (HR, 4.26; P = 0.020) and PSA mRNA (HR, 3.52; P = 0.042) expressions showed significantly worse mCRPC-PFS rates than those with low expression. Increased PSA and PSMA mRNA expressions were significantly associated with shorter PSA-PFS and radiological PFS in mCPRC, indicating an association with drug resistance.

CONCLUSIONS

PSMA and PSA mRNA expressions are associated with BCR in LPCa. In advanced prostate cancer, PSMA and PSA mRNA can also predict rapid progression from mHSPC to mCRPC and ARSI or taxane-based chemotherapy resistance.

Prostate-Specific Membrane Antigen: Gateway to Management of Advanced Prostate Cancer

Prostate-specific membrane antigen (PSMA) as a transmembrane protein is overexpressed by prostate cancer (PC) cells and is accessible for binding antibodies or low-molecular-weight radioligands due to its extracellular portion. Successful targeting of PSMA began with the development of humanized J591 antibody. Due to their faster clearance compared to antibodies, small-molecule radioligands for targeted imaging and therapy of PC have been favored in recent development efforts. PSMA positron emission tomography (PET) imaging has higher diagnostic performance than conventional imaging for initial staging of high-risk PC and biochemical recurrence detection/localization. However, it remains to be demonstrated how to integrate PSMA PET imaging for therapy response assessment and as an outcome endpoint measure in clinical trials. With the recent approval of 177Lu-PSMA-617 by the US Food and Drug Administration for metastatic castration-resistant PC progressing after chemotherapy, the high value of PSMA-targeted therapy was confirmed. Compared to standard of care, PSMA-based radioligand therapy led to a better outcome and a higher quality of life. This review, focusing on the advanced PC setting, provides an overview of different approved and nonapproved PSMA-targeted imaging and therapeutic modalities and discusses the future of PSMA-targeted theranostics, also with an outlook on non-radiopharmaceutical-based PSMA-targeted therapies.

Standardized PSMA-PET Imaging of Advanced Prostate Cancer

Imaging of advanced prostate cancer is a challenging task, as it requires longitudinal characterization of disease extent in a standardized way to enable appropriate treatment selection and evaluation of treatment efficacy. In the last years, prostate-specific membrane antigen (PSMA)-PET/CT has become the reference standard examination for patients with advanced prostate cancer. Together with the rise of PSMA-PET, standardized frameworks for the reporting of image findings have been proposed, eg, the Prostate Cancer Molecular Imaging Standardized Evaluation (PROMISE) and the structured reporting system for PSMA targeted PET imaging (PSMA-RADS) framework. Therefore, recent evidence on PSMA-PET derived tumor volume as useful a biomarker for outcome prognostication and related frameworks will be discussed in the article. The PROMISE framework recommends quantifying the tumor volume per-organ system, which accounts for the fact that the location of the metastases greatly influence its biological aggressiveness. In addition, changes in PSMA-PET derived tumor volume have been shown to be promising biomarkers for response assessment. Limitations of PSMA-PET will also be discussed because the tumor volume might not always be suited for response assessment. As a pitfall of PSMA-based systems, decreasing PSMA-expression might erroneously be interpreted as response to therapy. Also, especially for patients with limited disease, the tumor volume might not be ideal for response assessment. Therefore, various frameworks have been introduced to objectively measure response to therapy with PSMA-PET. Amongst these, the PSMA-PET progression (PPP) criteria and the response evaluation criteria in PSMA (RECIP) are optimized for earlier and later phenotypes of advanced prostate cancer, respectively. Variables needed to determine PPP or RECIP outcome on PSMA-PET are recorded under the umbrella of PROMISE recommendations. In this article, various reporting and response assessment frameworks are explained and discussed. Also, recent evidence for the relevance of PSMA-PET biomarkers for clinical management and outcome prognostication are shown.

Is There a Role of Interim PSMA PET in Chemotherapy of Prostate Cancer?

While RECIST 1.1 is well established in radiological response assessment, it is of limited use in prostate cancer (PCa) considering that the disease is often seen only as sclerotic bone changes on conventional imaging. Therefore, a molecular imaging-based response assessment including bone scans has been proposed and used in clinical trials, however, due to the flare phenomenon on bone scans this assessment leads to substantial delays in the detection of progression. Indeed, a robust and reliable imaging tool to assess response to chemotherapy in PCa is still warranted. Whether Positron Emission Tomography (PET) targeting the Prostate-Specific Membrane Antigen (PSMA) could achieve this, is still controversial. In this review, we summarized the available data on cytotoxic agents and their impact on PSMA expression, as well as the available data on PSMA PET imaging for response assessment.

Diagnostic Performance of 99mTc-iPSMA SPECT/CT in the Initial Staging of Patients with Unfavorable Intermediate-, High-, and Very High-Risk Prostate Cancer: A Comparative Analysis with 18F-PSMA-1007 PET/CT

Prostate cancer is a leading cause of cancer death in men worldwide. Imaging plays a key role in disease detection and initial staging. Emerging data has shown the superiority of PSMA imaging with PET/CT over conventional imaging for primary diagnoses. Single photon emission computed tomography is more available worldwide, and the imaging agent is low in cost. The aim of this study is to compare the diagnostic accuracy of 99mTc-EDDA/HYNIC-iPSMA SPECT/CT to 18F-PSMA-1007 PET/CT in the primary diagnosis of prostate cancer and the impact on clinical staging.

METHODS

In this prospective controlled study, 18 patients with histologically confirmed prostate cancer with unfavorable intermediate-, high-, and very high-risk characteristics were recruited to undergo 18F-PSMA-PET/CT and 99mTc-iPSMA SPECT/CT. The median age of the patients was 71 years old, and the median PSA level was 23.3 ng/mL. Lesions were divided into the prostate, seminal vesicles, lymph nodes, bone, and visceral metastases. Volumetric analysis was also performed between the two imaging modalities and correlated with PSA levels.

RESULTS

A total of 257 lesions were detected on 18F-PSMA-PET/CT: prostate (n = 18), seminal vesicles (n = 12), locoregional lymph nodes (n = 62), non-locoregional (n = 67), bone (n = 90), and visceral (n = 8). Of these, 99mTc-iPSMA-SPECT/CT detected 229 lesions, while both reviewers detected 100% of the lesions in the prostate (18/18), seminal vesicles (12/12), and visceral (8/8); LN LR (56/62; 90%), NLR (57/67; 85%), and bone (78/90; 86%). There were no statistically significant differences between volumetric parameters (t = -0.02122; p = 0.491596).

CONCLUSIONS

99mTc-iPSMA SPECT/CT is useful in the primary diagnosis of prostate cancer. Despite it showing a slightly lower lesion detection rate compared to 18F-PSMA PET/CT, it exhibited no impact on clinical staging and, consequently, the initial treatment intention.

68Ga-PSMA PET/CT for Response Evaluation of 223Ra Treatment in Metastatic Prostate Cancer

CT and bone scintigraphy are not useful for response evaluation of bone metastases to 223Ra treatment in metastatic castration-resistant prostate cancer (mCRPC). PET using 68Ga prostate-specific membrane antigen 11 (68Ga-PSMA) is a promising tool for response evaluation of mCRPC. The aim of this study was to determine the utility of 68Ga-PSMA PET/CT for response evaluation of 223Ra treatment in patients with mCRPC. Methods: Within this prospective, multicenter, imaging discovery study, 28 patients with mCRPC, eligible for 223Ra treatment, were included between 2019 and 2022. Patients received 223Ra according to the standard of care. Study procedures included CT, bone scintigraphy, and 68Ga-PSMA PET/CT at baseline, after 3 and 6 cycles of 223Ra treatment, and on treatment failure. Response to 223Ra treatment was visually assessed on all 3 imaging modalities. Total tumor volume within bone (TTVbone) was determined on 68Ga-PSMA PET/CT. Intrapatient heterogeneity in response was studied using a newly developed image-registration tool for sequential images of PET/CT. Results were compared with failure-free survival (good responders vs. poor responders; cutoff, 24 wk) and alkaline phosphatase (ALP) response after 3 cycles. Results: Visual response assessment criteria could not distinguish good responders from poor responders on 68Ga-PSMA PET/CT and bone scintigraphy. For 68Ga-PSMA PET/CT, TTVbone at baseline was lower in good responders than in poor responders, whereas TTVbone increased in both groups during treatment. TTVbone was higher in patients with new extraosseous metastases during 223Ra treatment. Although TTVbone and ALP correlated at baseline, changes in TTVbone and ALP on treatment did not. 68Ga-PSMA response of TTVbone showed intrapatient heterogeneity in most patients. Conclusion: mCRPC patients with lower TTVbone on 68Ga-PSMA PET/CT have the best clinical outcome after 223Ra treatment. Response is highly heterogeneous in most patients. A decrease in ALP, which occurred in most patients, was not correlated with a decrease in TTVbone, which might make one question the value of ALP for disease monitoring during 223Ra treatment in clinical practice.

Role of volumetric parameters obtained from 68 Ga-PSMA PET/CT and 18F-FDG PET/CT in predicting overall survival in patients with mCRPC receiving taxane therapy

OBJECTIVE

The aim of this study was to determine the prognostic role of volumetric parameters and Pro-PET scores obtained from 68 Ga-prostate-specific membrane antigen (PSMA) PET/CT and 18F-FDG PET/CT in patients with metastatic castration-resistant prostate cancer (mCRPC) receiving taxane therapy.

MATERIALS AND METHODS

The study included 71 patients who underwent simultaneous PSMA and 18F-FDG PET/CT imaging between January 2019 and January 2022, had a Pro-PET score of 3-5 and had received taxane therapy after imaging. 18F-FDG tumor volume (TV-F) and PSMA tumor volume (TV-P) values of the lesions and total lesion glycolysis (TL-G) and total lesion PSMA (TL-P) values of the lesions were calculated on both imaging studies and the effects of these parameters on overall survival (OS) were investigated.

RESULTS

The median age of the patients included herein was 71 years (56-89) and the median prostate-specific antigen (PSA) level was 16.4 (0.01-1852 ng/dL). According to the Kaplan-Meier survival analysis, TTV-P ≥ 78.5, TTL-P ≥ 278.8, TTV-F ≥ 94.98, TTL-G ≥ 458.3, TTV-P + F ≥ 195.45, TTL-G + P ≥ 855.78, lymph node (L)TV-FDG ≥ 3.4, LFDG-SUVmax ≥ 3.2, LFDG-SUVmean ≥ 2.25, LFDG-SUVpeak ≥ 2.55, and bone (B)TV-F ≥ 51.15 values were found to be prognostic factors in predicting short OS. Multivariate Cox regression analysis showed that a Vscore ≥ 3 (95% confidence interval [CI]: 7.069-98.251, p < 0.001) and TTL-G + P ≥ 855.78 (95% CI: 4.878-1037.860, p = 0.006) were found to be independent prognostic factors in predicting short OS.

CONCLUSION

Volumetric parameters and Pro-PET scores obtained from 68 Ga-PSMA PET/CT and 18F-FDG PET/CT imaging have been shown to have an impact on OS in patients with mCRPC receiving taxane therapy.

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.

SPECT at the speed of PET: a feasibility study of CZT-based whole-body SPECT/CT in the post 177Lu-DOTATATE and 177Lu-PSMA617 setting

PURPOSE

To evaluate the feasibility of using the StarGuide (General Electric Healthcare, Haifa, Israel), a new generation multi-detector cadmium-zinc-telluride (CZT)-based SPECT/CT, for whole-body imaging in the setting of post-therapy imaging of 177Lu-labeled radiopharmaceuticals.

METHODS

Thirty-one patients (34-89 years old; mean ± SD, 65.5 ± 12.1) who were treated with either 177Lu-DOTATATE (n=17) or 177Lu-PSMA617 (n=14) as part of standard of care were scanned post-therapy with the StarGuide; some were also scanned with the standard GE Discovery 670 Pro SPECT/CT. All patients had either 64Cu-DOTATATE or 18F-DCFPyL PET/CT prior to first cycle of therapy for eligibility check. The detection/targeting rate (lesion uptake greater than blood pool uptake) of large lesions meeting RECIST 1.1 size criteria on post-therapy StarGuide SPECT/CT was evaluated and compared to the standard design GE Discovery 670 Pro SPECT/CT (when available) and pre-therapy PET by two nuclear medicine physicians with consensus read.

RESULTS

This retrospective analysis identified a total of 50 post-therapy scans performed with the new imaging protocol from November 2021 to August 2022. The StarGuide system acquired vertex to mid-thighs post-therapy SPECT/CT scans with 4 bed positions, 3 min/bed and a total scan time of 12 min. In comparison, the standard GE Discovery 670 Pro SPECT/CT system typically acquires images in 2 bed positions covering the chest, abdomen, and pelvis with a total scan time of 32 min. The pre-therapy 64Cu-DOTATATE PET takes 20 min with 4 bed positions on GE Discovery MI PET/CT, and 18F-DCFPyL PET takes 8-10 min with 4-5 bed positions on GE Discovery MI PET/CT. This preliminary evaluation showed that the post-therapy scans acquired with faster scanning time using StarGuide system had comparable detection/targeting rate compared to the Discovery 670 Pro SPECT/CT system and detected large lesions defined by RECIST criteria on the pre-therapy PET scans.

CONCLUSION

Fast acquisition of whole-body post-therapy SPECT/CT is feasible with the new StarGuide system. Short scanning time improves the patients' clinical experience and compliance which may lead to increased adoption of post-therapy SPECT. This opens the possibility to offer imaged-based treatment response assessment and personalized dosimetry to patients referred for targeted radionuclide therapies.

PSMA PET/CT: joint EANM procedure guideline/SNMMI procedure standard for prostate cancer imaging 2.0

Here we aim to provide updated guidance and standards for the indication, acquisition, and interpretation of PSMA PET/CT for prostate cancer imaging. Procedures and characteristics are reported for a variety of available PSMA small radioligands. Different scenarios for the clinical use of PSMA-ligand PET/CT are discussed. This document provides clinicians and technicians with the best available evidence, to support the implementation of PSMA PET/CT imaging in research and routine practice.

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.

Using PSMA imaging for prognostication in localized and advanced prostate cancer

The use of prostate-specific membrane antigen (PSMA)-directed applications in modern prostate cancer management has evolved rapidly over the past few years, helping to establish new treatment pathways and provide further insights into prostate cancer biology. However, the prognostic implications of PSMA-PET have not been studied systematically, owing to rapid clinical implementation without long follow-up periods to determine intermediate-term and long-term oncological outcomes. Currently available data suggest that traditional prognostic factors and survival outcomes are associated with high PSMA expression (both according to immunohistochemistry and PET uptake) in men with localized and biochemically recurrent disease. Treatment with curative intent (primary and/or salvage) often fails when PSMA-positive metastases are present; however, the sensitivity of PSMA-PET in detecting all metastases is poor. Low PSMA-PET uptake in recurrent disease is a favourable prognostic factor; however, it can be associated with poor prognosis in conjunction with high ¹⁸F-fluorodeoxyglucose uptake in metastatic castration-resistant prostate cancer. Clinical trials embedding PSMA-PET for guiding management with reliable oncological outcomes are needed to support ongoing clinical use.

Systemic therapy response evaluation in prostate carcinoma with [68Ga]Ga-PSMA-11 PET/CT

Background

Consensus statements was published by EAU and EANM to clarify some uncertainties on PSMA PET/CT response assessment in 2020. We aimed to investigate the response criteria for PSMA PET/CT according to published criteria by comparing with serum PSA changes and determine the factors affecting therapy response evaluation.

Results

A high concordance was found between [68Ga]Ga-PSMA-11 PET/CT and serum PSA responses and 0.84 of Gamma coefficient was obtained. Between concordant and discordant group, statistically significant difference was not found in terms of received therapies and castration resistance status. Statistically significant but low correlation was found between serum PSA and SUV values of prostate, moderate correlation was found serum PSA and SUVmax values of metastatic lymph nodes and bones.

Conclusions

The response evaluation of PSMA PET/CT according to the published criteria shows high concordance with serum PSA values without being affected by received therapies or castration resistance. This criteria can be used with contribution of serum PSA values in response evaluation of prostate cancer according to our results and literature data.

Clinical Applications of PSMA PET Examination in Patients with Prostate Cancer

Simple Summary

The prostate specific membrane antigens, abbreviated as PSMAs, are type II membrane proteins that are highly ex-pressed on the surface of malignant prostate tissue in prostate cancer (PCa), particularly in aggressive, andro-gen-deprived, metastatic, and hormone-refractory PCa. Today, radionuclides that bind to these PSMA peptides are widely available for diagnostic and therapeutic purposes to specifically image and target prostate tumor cells at molec-ular level. In this descriptive review, we aimed to emphasize the usefulness of PSMA positron emission tomography (PET) examination in the management of patients with various stages of PCa. In addition, we outlined the main pitfalls and limitations of this scan to avoid misinterpretation of the results and to improve the decision making process in rela-tion to the patient’s further treatment. We concluded that PSMA PET examination in primary PCa patients has an es-sential role in the high-risk group. It is the new imaging standard in patients with in biochemical recurrence PCa and plays an important role in treatment decision. Furthermore, PSMA PET scan is a gold standard for the evaluation of PSMA targeted therapies in patients having progress of the disease. Future prospective studies, particularly on the im-pact of PSMA PET on therapy stratification, may further strengthen the role of PSMA in the treatment of PCa patients.

Abstract

With the progressive aging of the population in industrially developed countries, as well as advances in diagnostic and biopsy techniques and improvements in patient awareness, the incidence of prostate cancer (PCa) is continuously increasing worldwide. Therefore, PCa is currently considered as the second leading cause of tumor-related death. Early detection of the tumor and its metastasis is essential, as the rate of disease recurrence is high and occurs in 27% to 53% of all patients who underwent curative therapy with radical prostatectomy or local radiotherapy. In this regard, the prostate specific membrane antigens, abbreviated as PSMAs, are type II membrane proteins that are highly expressed on the surface of malignant prostate tissue in PCa, particularly in aggressive, androgen-deprived, metastatic, and hormone-refractory PCa, and they are inversely associated with the androgen level. Up to 95% of adenocarcinomas of the prostate express PSMA receptors on their surface. Today, radionuclides that bind to these PSMA peptides are widely accepted for diagnostic and therapeutic purposes to specifically image and target prostate tumor cells at the molecular level, a process referred to as targeted theranostics. Numerous studies have demonstrated that the integration of these peptides into diagnostic and therapeutic procedures plays a critical role in the primary staging and treatment decisions of especially high-risk PCa, expands therapeutic options for patients with advanced stage of prostate tumor, and prolongs patients’ survival rate. In this review article, we intend to briefly spotlight the latest clinical utilization of the PSMA-targeted radioligand PET imaging modality in patients with different stages of PCa. Furthermore, limitations and pitfalls of this diagnostic technique are presented.

Interval Changes in PSMA PET/CT During Radium-223 Therapy for Metastatic Bone Disease from Castration-Resistant Prostate Cancer

Background

Radium-223, an alpha-emitting therapeutic radiopharmaceutical, prolongs overall survival (OS) in patients with symptomatic bone-predominant metastatic castration-resistant prostate cancer (mCRPC). PSMA PET/CT is a molecular imaging tool for whole-body imaging of prostate cancer and may inform on the mechanisms of radium-223 activity and treatment resistance in mCRPC patients.

Methods

In an open-label, single-arm, prospective trial, we enrolled patients with bone-predominant mCRPC to undergo baseline PSMA PET/CT, 6 cycles of radium-223, and post-therapy PSMA PET/CT. We assessed the relationship between multiple parameters of interval change on PSMA PET/CT on aPROMISE PSMA automated analysis and a human reader, and laboratory measurements.

Results

Fourteen patients were enrolled and 9 patients completed both protocol-defined PSMA PET/CT. Of the 9 evaluable patients, 1 (11%) had a complete response and 8 (89%) had PSMA PET progressive disease. All patients showed decreases in PSMA uptake in some disease sites evident on the baseline scan. The change in overall burden of disease on PSMA PET was more strongly correlated with changes in PSA (ρ = 0.95) than ALP (ρ = 0.62). Progression in bone was a common finding on post-treatment PSMA PET/CT.

Conclusion

PSMA PET was able to assess response in individual lesions during radium-223 therapy in mCRPC patients. PSMA PET responses in previously established disease sites were universal, but most patients also showed overall PSMA PET progression during 6 cycles of radium-223. Given high correlation with changes in PSA, PSMA PET may be of limited value in follow-up during or after radium-223 in bone-predominant mCRPC.

Graphical abstract

Diagnostic Performance of Prostate-specific Membrane Antigen Positron Emission Tomography-targeted biopsy for Detection of Clinically Significant Prostate Cancer: A Systematic Review and Meta-analysis

CONTEXT

Prostate-specific membrane antigen positron emission tomography (PSMA-PET) has gained acceptance as a staging tool for prostate cancer (PCa). Recent reports suggest an association between PSMA PET and detection of clinically significant PCa (csPCa) on prostate biopsy.

OBJECTIVE

To assess the diagnostic accuracy of PSMA PET-targeted biopsy (PSMA-PET-TB) for csPCa detection.

EVIDENCE ACQUISITION

We searched PubMed, Web of Science, and Scopus in December 2021 to identify studies assessing the accuracy of PSMA-PET-TB for csPCa detection. A diagnostic meta-analysis was performed to calculate pooled sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of PSMA-PET-TB alone and in combination with magnetic resonance imaging (MRI)-TB for detecting csPCa.

EVIDENCE SYNTHESIS

Overall, five prospective studies involving 497 patients were eligible for this meta-analysis. For csPCa detection, PSMA-PET-TB had pooled sensitivity, specificity, PPV, and NPV of 0.89 (95% confidence interval [CI] 0.85-0.93), 0.56 (95% CI 0.29-0.80), 0.69 (95% CI 0.58-0.79), and 0.78 (95% CI 0.50-0.93), respectively. Among the three studies assessing the PSMA-PET + MRI-TB strategy, the pooled sensitivity, specificity, PPV, and NPV for csPCa detection were 0.91 (95% CI 0.77-0.97), 0.64 (95% CI 0.40-0.82), 0.75 (95% CI 0.56-0.87), and 0.85 (95% CI 0.62-0.95), respectively. For lesions with a Prostate Imaging-Reporting and Data System (PI-RADS) score of 3, the sensitivity, specificity, PPV, and NPV were 0.69, 0.73, 0.48, and 0.86, respectively.

CONCLUSIONS

PSMA-PET-TB appears to have favorable diagnostic accuracy for csPCa detection and combination with MRI seems to improve this. According to our meta-analysis, PSMA-PET has promising clinical application for detection of csPCa, namely in the case of PI-RADS 3 lesions. Further prospective studies are needed to explore the true clinical utility of a PSMA-PET-based diagnostic pathway.

PATIENT SUMMARY

Prostate-specific membrane antigen positron emission tomography (PSMA-PET) is a promising imaging method for detecting clinically significant prostate cancer and seems to have additional value to magnetic resonance imaging (MRI) for detection.

Feasibility and Optimal Time Point of [68Ga]Gallium-labeled Prostate-specific Membrane Antigen Ligand Positron Emission Tomography Imaging in Patients Undergoing Cytoreductive Surgery After Systemic Therapy for Primary Oligometastatic Prostate Cancer: Implications for Patient Selection and Extent of Surgery

Background

Prostate-specific membrane antigen (PSMA) targeted molecular imaging using positron emission tomography (PET) has significantly improved the diagnosis and treatment of prostate cancer (PCA).

Objective

To assess the feasibility and compare the diagnostic accuracy of [⁶⁸Ga]Ga-PSMA-11 PET images taken at baseline, before the initiation of systemic treatment and preoperative images, using histopathology after cytoreductive surgery as reference.

Design, setting, and participants

We identified 20 patients in our prospectively maintained database with primary oligometastatic PCA who underwent cytoreductive radical prostatectomy and superextended pelvic lymph node dissection after systemic therapy, who had baseline and preoperative [⁶⁸Ga]Ga-PSMA-11 PET imaging available.

Outcome measurements and statistical analysis

We performed a region-based analysis to determine the diagnostic accuracy of imaging, using pathology as a reference. Regions were predefined as prostate, internal iliac left/right, obturator left/right, external iliac left/right, common iliac left/right, and presacral.

Results and limitations

Sensitivity, specificity, negative predictive value (NPV), positive predictive value (PPV), and diagnostic effectiveness were, respectively, 95.65%, 78.22%, 98.39%, 57.89%, and 83.00% for baseline [⁶⁸Ga]Ga-PSMA-11 PET, compared to 56.52%, 98.05%, 88.30%, 89.66%, and 88.50% for preoperative [⁶⁸Ga]Ga-PSMA-11 PET. On a receiver operating characteristic analysis, the diagnostic accuracy of baseline [⁶⁸Ga]Ga-PSMA-11 PET with an area under the curve (AUC) of 0.87 (95% confidence interval [CI] 0.83–0.92) was significantly better than that of preoperative [⁶⁸Ga]Ga-PSMA-11 PET after systemic therapy with an AUC of 0.77 (95% CI 0.70–0.85, p = 0.01).

Conclusions

Baseline imaging, [⁶⁸Ga]Ga-PSMA-11 PET has significantly better diagnostic accuracy, sensitivity, and NPV than images obtained preoperatively, in systemically pretreated patients. If a patient is suitable for local treatment and complete resection of the residual tumor is intended, [⁶⁸Ga]Ga-PSMA-11 PET images taken prior to systemic therapy are significantly more accurate in selecting the relevant lymph nodes for resection.

Patient summary

We found that prostate-specific membrane antigen positron emission tomography (PSMA-PET) imaging used early, before hormonal therapy or chemotherapy, provides more accurate information about the spread of the disease, than if used immediately before surgery but after hormonal therapy or chemotherapy. Early use of PSMA-PET has the potential to improve therapy also at later stages of the disease.

The role of prostate-specific membrane antigen PET/computed tomography in the management of prostate cancer patients: could we ask for more?

PURPOSE OF REVIEW

Thanks to the development of novel PSMA-based peptides, molecular imaging, such as PET/CT paired with theranostic-based approaches have recently been proposed for treatment of prostate cancer. Patient selection, however, remains challenging because of the absence of strong prospective data to interpret and translate imaging scans into effective and well tolerated treatment regimens.

RECENT FINDINGS

In this review, we discuss the latest findings in PSMA imaging in prostate cancer patients. Particularly, we go into detail into the impact of PSMA imaging on the treatment management in primary staging, biochemical recurrence and in advanced prostate cancer.

SUMMARY

For primary prostate cancer staging, PSMA PET/CT seems crucial for primary therapy assessment, being able in some cases to detect lesions outside the surgical template, thus permitting a change in management. Moreover, N+ condition at PSMA has been correlated with a worse biochemical recurrence-free and therapy-free survival. The early detection of PSMA-positive findings in recurrent prostate cancer is associated with a better time to relapse survival. Similarly, for advanced prostate cancer patients, accurate restaging with PSMA imaging is gaining importance for early prediction of response to systemic therapies and to assure the best outcome possible. With regards to theranostics, appropriate selection of patients eligible for 177Lu-PSMA requires PSMA imaging, whereas the role of added FDG-PET for discriminating those with PSMA/FDG discordance needs to be further evaluated.

Reduced Segmentation of Lesions Is Comparable to Whole-Body Segmentation for Response Assessment by PSMA PET/CT: Initial Experience with the Keyhole Approach

(1) Background: Prostate-specific membrane antigen (PSMA) positron emission tomography (PET)-derived parameters, such as the commonly used standardized uptake value (SUV) and PSMA-positive tumor volume (PSMA-TV), have been proposed for response assessment in metastatic prostate cancer (PCa) patients. However, the calculation of whole-body PSMA-TV remains a time-consuming procedure. We hypothesized that it may be possible to quantify changes in PSMA-TV by considering only a limited number of representative lesions. (2) Methods: Sixty-five patients classified into different disease stages were assessed by PSMA PET/CT for staging and restaging after therapy. Whole-body PSMA-TV and whole-body SUVmax were calculated. We then repeated this calculation only including the five or ten hottest or largest lesions. The corresponding serum levels of prostate-specific antigen (PSA) were also determined. The derived delta between baseline and follow-up values provided the following parameters: ΔSUVmaxall, ΔSUVmax10, ΔSUVmax5, ΔPSMA-TVall, ΔPSMA-TV10, ΔPSMA-TV5, ΔPSA. Finally, we compared the findings from our whole-body segmentation with the results from our keyhole approach (focusing on a limited number of lesions) and correlated all values with the biochemical response (ΔPSA). (3) Results: Among patients with metastatic hormone-sensitive PCa (mHSPC), none showed a relevant deviation for ΔSUVmax10/ΔSUVmax5 or ΔPSMA-TV10/ΔPSMA-TV5 compared to ΔSUVmaxall and ΔPSMA-TVall. For patients treated with taxanes, up to 6/21 (28.6%) showed clinically relevant deviations between ΔSUVmaxall and ΔSUVmax10 or ΔSUVmax5, but only up to 2/21 (9.5%) patients showed clinically relevant deviations between ΔPSMA-TVall and ΔPSMA-TV10 or ΔPSMA-TV5. For patients treated with radioligand therapy (RLT), up to 5/28 (17.9%) showed clinically relevant deviations between ΔSUVmaxall and ΔSUVmax10 or ΔSUVmax5, but only 1/28 (3.6%) patients showed clinically relevant deviations between ΔPSMA-TVall and ΔPSMA-TV10 or ΔPSMA-TV5. The highest correlations with ΔPSA were found for ΔPSMA-TVall (r ≥ 0.59, p ≤ 0.01), followed by ΔPSMA-TV10 (r ≥ 0.57, p ≤ 0.01) and ΔPSMA-TV5 (r ≥ 0.53, p ≤ 0.02) in all cohorts. ΔPSA only correlated with ΔSUVmaxall (r = 0.60, p = 0.02) and with ΔSUVmax10 (r = 0.53, p = 0.03) in the mHSPC cohort, as well as with ΔSUVmaxall (r = 0.51, p = 0.01) in the RLT cohort. (4) Conclusion: Response assessment using PSMA-TV with a reduced number of lesions is feasible, and may allow for a simplified evaluation process for PSMA PET/CT.

Biomarkers to personalize treatment with 177Lu-PSMA-617 in men with metastatic castration-resistant prostate cancer - a state of the art review

Radioligand therapy with Lutetium-177 (177Lu)-Prostate-specific membrane antigen (PSMA) has shown to prolong survival in metastatic castration resistant prostate cancer (mCRPC). One of the major challenges for clinicians in the future is to select those patients who would benefit most from this therapy to position it in the treatment landscape of mCRPC. This, in turn, will lead to the delivery of personalized therapies. In this narrative review article we summarize recent studies investigating both predictive and prognostic clinical, imaging-based, and molecular biomarkers to predict treatment response to 177Lu-PSMA-617 radioligand therapy with the aim of identifying men who should be considered for this approach. Of note, the evidence on the role of biomarkers currently relies on small retrospective trials and their validation in larger prospective cohorts is necessary before these results can be translated in the clinical practice.

Beyond the Prognostic Value of 2-[18F]FDG PET/CT in Prostate Cancer: A Case Series and Literature Review Focusing on the Diagnostic Value and Impact on Patient Management

The role of 2-deoxy-2-[¹⁸F]fluoro-D-glucose Positron Emission Tomography/Computed Tomography (FDG PET/CT) in the management of prostate cancer (PCa) patients is increasingly recognised. However, its clinical role is still controversial. Many published studies showed that FDG PET/CT might have a prognostic value in the metastatic castration-resistant phase of the disease, but its role in other settings of PCa and, more importantly, its impact on final clinical management remains to be further investigated. We describe a series of six representative clinical cases of PCa in different clinical settings, but all characterised by a measurable clinical impact of FDG PET/CT on the patients’ management. Starting from their clinical history, we report a concise narrative literature review on the advantages and limitations of FDG PET/CT beyond its prognostic value in PCa. What emerges is that in selected cases, this imaging technique may represent a useful tool in managing PCa patients. However, in the absence of dedicated studies to define the optimal clinical setting of its application, no standard recommendations on its use in PCa patients can be made.

Global experience with PSMA-based alpha therapy in prostate cancer

PURPOSE

This review discusses the current state of prostate-specific membrane antigen (PSMA)-based alpha therapy of metastatic castration-resistant prostate cancer (mCRPC). With this in-depth discussion on the growing field of PSMA-based alpha therapy (PAT), we aimed to increase the interactions between basic scientists and physician-scientists in order to advance the field.

METHODS

To achieve this, we discuss the potential, current status, and opportunities for alpha therapy and strategies, attempted to date, and important questions that need to be addressed. The paper reviews important concepts, including whom to treat, how to treat, what to expect regarding treatment outcome, and toxicity, and areas requiring further investigations.

RESULTS

There is much excitement about the potential of this field. Much of the potential exists because these therapies utilize unique mechanisms of action, difficult to achieve with other conventional therapies.

CONCLUSION

A better understanding of the strengths and limitations of PAT may help in creating an effective therapy for mCRPC and design a rational combinatorial approach to treatment by targeting different tumor pathways.

Efficacy of 68Ga-PSMA PET/CT-derived whole-body volumetric parameters in predicting response to second-generation androgen receptor axis-targeted therapy, and the prognosis in metastatic hormone-refractory prostate cancer patients

INTRODUCTION

The present study investigates the role of 68Ga-PSMA PET/CT-derived whole-body metabolic and volumetric parameters in the prediction of treatment response and prognosis among metastatic hormone-refractory prostate cancer patients undergoing second-generation androgen receptor axis-targeted therapy (abiraterone or enzalutamide).

MATERIALS AND METHODS

This retrospective study included 44 metastatic hormone-refractory prostate cancer patients undergoing 68Ga-PSMA PET/CT, including 29 enzalutamide-treated and 15 abiraterone-treated patients.

RESULTS

Of the 44 patients included in the study, 29 received enzalutamide and 15 received abiraterone. During treatment, the changes in PET parameters were correlated with the PSA (biochemical) response. More specifically, a positive correlation was noted between PSA response and percent change in TLP (ΔTLP) response, and there was concordance between the results (r = 0.652, k = 0.42, P < 0.001). Baseline PSA (P =0.05), high MTVw (P = 0.005), the increase in ΔPSA (P = 0.036), ΔTLP (P = 0.039) and percent change in MTV (ΔMTV) (P = 0.049) values were identified as factors associated with mortality risk.Multivariate analysis showed that PSA1 [odds ratio (OR): 1.005, 95% confidence interval (CI) 1.002-1.008, P = 0.004], ΔPSA (OR: 14.7, 95% CI 1.50-143.7, P = 0.02) and MTVw1 (OR: 11.4, 95% CI 1.11-116, 6, P = 0.04) were independent prognostic factors associated with mortality risk.

CONCLUSION

A statistically significant concordance and correlation was noted between 68Ga-PSMA PET/CT-derived whole-body metabolic parameters (ΔTLP and ΔMTV) and ΔPSA. In addition, the baseline PSA, ΔPSA, ΔTLP, ΔMTV and TMTV were identified as predictive factors for mortality risk.

68Ga-PSMA PET/CT for response assessment and outcome prediction in metastatic prostate cancer patients treated with taxane-based chemotherapy

Aim: We aimed to evaluate the role of Positron Emission Tomography (PET) targeting the Prostate-Specific Membrane Antigen (PSMA) for response assessment in metastatic prostate cancer (mPCa) patients treated with taxane-based chemotherapy (docetaxel or cabazitaxel) and its predictive value on patient outcome. Methods: We retrospectively evaluated 37 patients with metastatic hormone-sensitive or castration-resistant prostate cancer (mHSPC or mCRPC) who underwent ⁶⁸Ga-PSMA-11 PET/CT at baseline and after the last cycle of taxane-based chemotherapy (docetaxel or cabazitaxel) without treatment modification between scans. Biochemical response (BR) was defined as an undetectable or decreased prostate-specific antigen (PSA) by ≥50% compared to baseline. Association between BR and different PET parameters were tested. A cut-off of ≥30% change in PSMA total tumor volume (PSMA-TV) was used to define PSMA responders (PSMA-R) vs PSMA non-responders (PSMA-NR). Correlation between PSMA-PET/CT response and BR was evaluated using the Phi coefficient. Association between PET-response and overall survival (OS) was performed using Cox regression and Kaplan-Meier method. Results: Our cohort was composed of 8 (22%) mHSPC and 29 (78%) mCRPC patients. Twenty-one patients received docetaxel, and 16 received cabazitaxel treatment (median: 6 cycles, interquartile (IQR):5-8). BR was found in 18/37 patients. Using PSMA-TV, PSMA-PET/CT response was concordant with BR in 35/37 patients (Phi=0.89, p<0.0001). There were 18/37 PSMA-R (6 complete response and 12 partial response) and 19/37 PSMA-NR (17 progressive disease and 2 stable disease). After a median follow-up of 23 months there was a statistically significant longer overall survival (OS) for PSMA-R compared to PSMA-NR (median OS not reached vs 12 months, respectively, HR 0.10; 95%CI: 0.03-0.39, P = 0.001) for the entire population. Among the mCRPC subgroup, differences in OS were also observed (median 22 vs 12 months respectively, HR 0.22, 95%CI: 0.06-0.82, P = 0.023) with a 12-month OS rate of 100% for PSMA-R and 52% for PSMA-NR (P = 0.011). Conclusion: This retrospective analysis suggests that ⁶⁸Ga-PSMA-11 PET/CT is a promising imaging modality for assessing response to taxane-based chemotherapy in mPCa. PSMA-expression changes might be used as a predictive biomarker for OS which might help tailor individual therapy and select eligible patients for clinical trials.

Evaluation of [68Ga]Ga-PSMA PET/CT for therapy response assessment of [177Lu]Lu-PSMA radioligand therapy in metastasized castration refractory prostate cancer and correlation with survival

PURPOSE

The aim of this retrospective study was to evaluate the use of [68Ga]Ga-PSMA PET/CT in therapy response assessment (TRA) of mCRPC patients treated with [177Lu]Lu-PSMA-617 and its correlation with overall survival (OS).

METHODS

Thirty-nine patients were included in the study. Patient-/lesion-based early and late response assessment (ERA/LRA) was defined as PET2 (after two therapy cycles) vs. PET1 (before the first cycle) (n = 29) and end of treatment PET vs. PET1 (n = 17), respectively. PET-based response (PET parameters; modified (m) PERCIST/EORTC), biochemical response (ΔPSA; category-based) and category-based clinical response (CRA) was tested for correlation/agreement. PET-based TRA was correlated with OS.

RESULTS

A significant correlation/agreement was shown between PET parameters and CRA as well as biochemical response in LRA of all lesions and between mPERCIST-based and category-based PSA response assessment in LRA (bone lesion-based, P = 0.045, κ = 0.184). At ERA, OS was significantly higher in CR/PR/SD compared to progressive disease applying mPERCIST/EORTC criteria (P = 0.0024).

CONCLUSION

In [177Lu]Lu-PSMA-617-treated mCRPC patients OS of the group of CR/PR/SD was significantly higher compared to the progressive disease group (mPERCIST/EORTC) in ERA. Therefore, [68Ga]Ga-PSMA PET might serve as a complementary diagnostic tool for TRA offering prognostic value regarding OS.

18F DCFPyL PET Acquisition, Interpretation and Reporting: Suggestions Post Food and Drug Administration Approval

¹⁸F-DCFPyL was recently approved by the FDA for evaluation prior to definitive therapy and for biochemical recurrence. Here we focus on the key data that justify the clinical use of ¹⁸F-DCFPyL, as well as those aspects of protocol implementation and image interpretation that are important to the nuclear medicine physicians and radiologists who will interpret ¹⁸F-DCFPyL PET/CT and PET/MR scans.

Radium-223 Treatment of Patients with Metastatic Castration Resistant Prostate Cancer: Biomarkers for Stratification and Response Evaluation

Simple Summary

Radium-223 dichloride ([²²³Ra]RaCl₂; Ra-223) is an alpha-emitting radiopharmaceutical treatment for patients with metastatic castration resistant prostate cancer (mCRPC) with predominantly bone metastases. While responses to chemotherapeutic and antihormonal mCRPC treatments can be assessed by serum PSA levels, a decrease of serum PSA levels is not expected during Ra-223 therapy. Moreover, radiographic evaluation of bone metastases response is challenging. Therefore, novel biomarkers to select patients for Ra-223 treatment and monitoring response are urgently needed. In this review, we discuss the currently used and exploratory biomarkers for this purpose, including soluble and cellular factors detected in the peripheral blood, genetic defects and radiographic assessments. We conclude that some biomarkers, including metabolic products of collagen degradation and novel PET scan techniques, might hold promise as predictors of response to Ra-223 treatment. However, these biomarkers have not been extensively studied. Consequently, currently, no biomarker has established a place in patient stratification and response evaluation.

Abstract

Radium-223 dichloride ([²²³Ra]RaCl₂; Ra-223) is a targeted alpha-emitting radiopharmaceutical which results in an overall survival and health related quality of life (HRQoL) benefit in symptomatic patients with metastatic castration resistant prostate cancer (mCRPC) and predominantly bone metastasis. Although effective, options to select patients who will derive treatment benefit and to monitor and predict treatment outcomes are limited. PSA response and radiographic evaluation are commonly used in mCRPC treatment assessment but are not informative in Ra-223 treated patients. Consequently, there is a clear need for predictive and prognostic tools. In this review, we discuss the physiology of bone metastases and the mechanism of action and efficacy of Ra-223 treatment, as well as offering an outline of current innovative prognostic and predictive biomarkers.

Prostate-specific membrane antigen (PSMA)-based imaging in localized and advanced prostate cancer: a narrative review

Combined molecular and morphologic imaging modalities have emerged in recent years as an alternative to conventional imaging in prostate cancer (PC). In particular, novel prostate-specific membrane antigen (PSMA) radiotracers have demonstrated increased sensitivity and specificity for the initial staging of men with clinically localized PC, as well as for PC detection in the setting of biochemical recurrence (BCR). Molecular imaging is increasingly used to guide treatment decisions in these patients—though its impact on survival has yet to be established. Improved PC detection in men with BCR has also helped to identify a subset of patients with oligometastatic disease. The optimal management of oligometastatic PC and the role of metastasis-directed therapies (MDT) are the subjects of ongoing studies. In comparison to clinically localized or biochemically recurrent PC, the role of molecular imaging in men with advanced disease is less established. In metastatic castration-resistant PC (mCRPC), PSMA-based imaging has primarily been investigated as a companion diagnostic tool to predict and monitor response to PSMA-targeted radioligand therapy (RLT). More recent efforts have focused on using molecular imaging to monitor treatment response to conventional chemohormonal therapies. However, despite promising early results, several barriers remain to the widespread use of PSMA-based imaging in metastatic PC: temporary flares in PSMA uptake have been described in a subset of patients after initiation of therapy, and the underlying mechanism and clinical implications of this phenomenon are still poorly understood. Furthermore, whereas PSMA is invariably expressed in hormone-sensitive PC, loss of PSMA expression is increasingly recognized in a subset of mCRPC patients with aggressive disease. Although this may limit the use of PSMA-based imaging as a standalone modality in advanced PC, loss of PSMA uptake may also provide non-invasive and clinically relevant molecular insight on patients’ underlying tumor biology.

Diagnostic potential of serum extracellular vesicles expressing prostate-specific membrane antigen in urologic malignancies

We aimed to develop a sandwich ELISA to detect prostate-specific membrane antigen (PSMA) on small extracellular vesicles (EVs) using T-cell immunoglobulin domain and mucin domain-containing protein 4 (Tim4) as a capture molecule for EVs and to evaluate its diagnostic potential in urologic malignancies. First, we optimized the conditions for sandwich ELISA measuring the PSMA level on EVs captured from serum by Tim4 and found that the use of highly-purified EVs released from Tim4 that had captured EVs in serum reduced the background. Second, we confirmed its validity by studying mouse xenograft model for prostate cancer (PC). Lastly, we measured PSMA-EVs in serum of patients with urologic malignancies. The PSMA-EV levels were significantly higher in metastatic PC and castration-resistant PC (CRPC) patients than in therapy-naïve PC patients. In renal cell carcinoma (RCC) patients, PSMA-EVs were elevated in those with metastasis compared with those without metastasis, which may reflect the development of the neovasculature positive for PSMA in tumors. In conclusion, we developed a sandwich ELISA for detection of PSMA-EVs using highly-purified EVs isolated from serum by Tim4. Our results suggest that PSMA-EVs may be useful to diagnose and monitor not only PC but also RCC and possibly other hypervascular solid tumors.

Assessment of the viability and treatment response of bone metastases in patients with metastatic castration-resistant prostate cancer using choline PET/CT

This study aimed to evaluate the clinical use of choline-PET/CT for discriminating viable progressive osteoblastic bone metastasis from benign osteoblastic change induced by the treatment effect and evaluating the response of bone metastasis to treatment in metastatic castration-resistant prostate cancer (mCRPC) patients. Thirty patients with mCRPC underwent a total of 56 11C-choline-PET/CT scans for restaging, because 4 patients received 1 scan and 26 had 2 scans. Using 2 (pre- and post-treatment) 11C-choline-PET/CT examinations per patient, treatment response was assessed according to European Organization for Research and Treatment of Cancer (EORTC) criteria in 20 situations, in which only bony metastases were observed on 11C-choline-PET/CT scans. Viable bone metastases and osteoblastic change induced by the treatment effect were identified in 53 (94.6%) and 29 (51.8%) of 56 11C-choline-PET/CT scans, respectively. In 27 cases (48.2%), 11C-choline-PET/CT scans could discriminate the 2 entities. The mean SUVmax of the metastatic bony lesions was 5.82 ± 3.21, 5.95 ± 3.96, 6.73 ± 5.04, and 7.91 ± 3.25 for the osteoblastic, osteolytic, mixed, and invisible types, respectively. Of the 20 situations analyzed, CMR, PMR, SMD, and PMD, as determined by the EORTC, were seen in 1, 2, 3, and 14 cases, respectively. Of the 13 patients with increasing PSA trend, all 13 showed PMD. Of the 2 patients with PSA response of <50%, both 2 showed SMD. Of the 5 patients with PSA response of ≥50%, 1 showed CMR, 2 showed PMR, 1 showed SMD, and 1 showed PMD. Choline-PET/CT is very useful to discriminate viable progressive osteoblastic bone metastasis from osteoblastic change, and assess treatment response of bone metastases in mCRPC.

Feasibility of Different Tumor Delineation Approaches for 18F-PSMA-1007 PET/CT Imaging in Prostate Cancer Patients

Background

Delineation of PSMA-positive tumor volume on PET using PSMA-ligands is of highest clinical interest as changes of PSMA-PET/CT-derived whole tumor volume (WTV) have shown to correlate with treatment response in metastatic prostate cancer patients. So far, WTV estimation was performed on PET using ⁶⁸Ga-labeled ligands; nonetheless, ¹⁸F-labeled PET ligands are gaining increasing importance due to advantages over ⁶⁸Ga-labeled compounds. However, standardized tumor delineation methods for ¹⁸F-labeled PET ligands have not been established so far. As correlation of PET-based information and morphological extent in osseous and visceral metastases is hampered by morphological delineation, low contrast in liver tissue and movement artefacts, we correlated CT-based volume of lymph node metastases (LNM) and different PET-based delineation approaches for thresholding on ¹⁸F-PSMA-1007 PET.

Methods

Fifty patients with metastatic prostate cancer, ¹⁸F-PSMA-1007 PET/CT and non-bulky LNM (short-axis diameter ≥10mm) were included. Fifty LNM were volumetrically assessed on contrast-enhanced CT (volumetric reference standard). Different approaches for tumor volume delineation were applied and correlated with the reference standard: I) fixed SUV threshold, II) isocontour thresholding relative to SUV_max (SUV%), and thresholds relative to III) liver (SUV_liver), IV) parotis (SUV_parotis) and V) spleen (SUV_spleen).

Results

A fixed SUV of 4.0 (r=0.807, r² = 0.651, p<0.001) showed the best overall association with the volumetric reference. 55% SUV_max (r=0.627, r² = 0.393, p<0.001) showed highest association using an isocontour-based threshold. Best background-based approaches were 60% SUV_liver (r=0.715, r² = 0.511, p<0.001), 80% SUV_parotis (r=0.762, r² = 0.581, p<0.001) and 60% SUV_spleen (r=0.645, r² = 0.416, p<0.001). Background tissues SUV_liver, SUV_parotis & SUV_spleen did not correlate (p>0.05 each). Recently reported cut-offs for intraprostatic tumor delineation (isocontour 44% SUV_max, 42% SUV_max and 20% SUV_max) revealed inferior association for LNM delineation.

Conclusions

A threshold of SUV 4.0 for tumor delineation showed highest association with volumetric reference standard irrespective of potential changes in PSMA-avidity of background tissues (e. g. parotis). This approach is easily applicable in clinical routine without specific software requirements. Further studies applying this approach for total tumor volume delineation are initiated.

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

Prostate-specific membrane antigen positron emission tomography (PSMA PET) has recently gained interest as a promising tool for treatment response evaluation in metastatic castration-resistant prostate cancer (CRPC). We performed a systematic review and meta-analysis assessing the concordance between response evaluation using PSMA PET and serum prostate-specific antigen (PSA) level after systemic treatment and the association between PSMA PET and overall survival in metastatic CRPC patients. PubMed, Embase, and Cochrane library databases were searched until August 2020. Studies that reported the concordance between PSMA PET and PSA response were included. PSMA PET and PSA response evaluation were dichotomized into response vs. non-response to construct two-by-two contingency tables; an ≥30% increase in PSMA PET according to PET Response Criteria in Solid Tumors 1.0 and as an increase in serum PSA level of ≥25% as per Prostate Cancer Working Group 3 guidelines were defined as non-response. The percent agreement rates were pooled using random-effect model. Ten studies (268 patients) were included. The concordance rates ranged 0.50–0.84 with a pooled proportion of 0.73 (95% confidence interval 0.67–0.79). Patients were treated with ¹⁷⁷Lu-PSMA therapy in five, chemotherapy in three, ²²³Ra in one, and more than one type in one study. Various PET parameters were used: the most widely evaluated was PSMA tumor volume (PSMA-TV). Similar proportions were found across different therapeutic agents, PET response parameters, and regarding directionality of discordance (PSA response/PSMA non-response vs. PSMA response/PSA non-response). Two studies reported that a decrease in PSMA-TV was associated with better overall survival. PSMA PET and PSA response assessments were discordant in nearly a fourth of metastatic CRPC patients. Further studies are warranted to establish the clinical meaning of this discordance and define appropriate management for such clinical situation.

Assessing Response to [177Lu]PSMA Radioligand Therapy using modified PSMA PET Progression Criteria

Introduction: Positron emission tomography/computer tomography (PET/CT) targeting the prostate specific membrane antigen (PSMA) plays a key role in staging of patients with prostate cancer (PCa). Moreover, it is not only used for the assessment of adequate PSMA expression of PCa cells before PSMA-targeting radioligand therapy (PSMA RLT) but also for re-staging during the course of therapy to evaluate response to treatment. Whereas no established criteria exist for systematic response evaluation so far, recently proposed PSMA PET Progression (PPP) criteria might fill this gap. The aim of this study was to assess the feasibility of PPP criteria in patients undergoing PSMA RLT and their prognostic implications. Methods: In this retrospective analysis, PSMA PET/CT scans of 46 patients acquired before and after completion of PSMA RLT were analyzed separately by two readers using modified PPP criteria. After interobserver agreement assessment, consensus results (progressive vs. non-progressive disease) were compared in a multivariate cox regression model (endpoint overall survival, OS). Results: Interobserver agreement on modified PPP criteria was substantial (Cohens κ = 0.73) with a concordance in 87% of patients. Median OS of all patients after PSMA RLT (n = 46) was 9.0 [95% confidence interval (CI) 7.8 - 10.2] months. Progression according to modified PPP criteria was found in 32 patients and was a significant (p ≤0.001) prognostic marker for OS with a hazard ratio of 15.5 [95% CI 3.4 - 70.2]. Conclusion: Response assessment in patients undergoing PSMA RLT using modified PPP criteria are reproducible and highly prognostic for OS. Modified PPP criteria should be validated in future prospective trials.

Accurate Monitoring of the Response of Bone Metastases to Treatment in Patients with Prostate Cancer Using Choline PET/CT

We here report 2 cases of castration-resistant prostate cancer (CRPC) observed two times on ¹¹C-choline positron emission tomography computed tomography (PET/CT), which was useful to discriminate viable progressive osteoblastic bone metastasis from benign osteoblastic change induced by the treatment effect and to determine the viability of bone metastases, regardless of whether sclerosis was present or not. Because one case demonstrated disappearance of abnormal ¹¹C-choline uptake of osteoblastic metastatic lesions after abiraterone therapy and no new lesions at other sites, suggesting nonviable bone metastases, we can assume a complete metabolic response. Because the other case demonstrated a decrease in the existing, abnormal ¹¹C-choline uptake of osteoblastic metastatic lesions, but multiple new appearances of osteoblastic and nonosteoblastic lesions with abnormal ¹¹C-choline uptake after radium-223 therapy suggesting multiple viable bone metastases, we can assume progressive metabolic disease. ¹¹C-choline PET/CT could help in assessing the treatment response of bone metastases in patients with metastatic CRPC.

Current and Emerging Clinical Applications of PSMA PET Diagnostic Imaging for Prostate Cancer

Prostate-specific membrane antigen (PSMA) is highly expressed on most prostate cancer (PCa) cells, and several PSMA ligands for PET imaging are now available worldwide. ⁶⁸Ga-PSMA-11 has already received U.S. Food and Drug Administration and European Medicines Agency approval, and use of PSMA PET is currently suggested by several international guidelines for investigating PCa in different clinical settings. In primary PCa, PSMA PET has been shown to be superior to cross-sectional imaging for the detection of pelvic lymph nodes and distant metastases with subsequent clinical management changes. Additionally, it might also have a role in intraprostatic tumor localization, especially when combined with multiparametric MRI. In a setting of PCa recurrence, higher detection rates have been observed than for any other available imaging techniques, especially at low prostate-specific antigen values. Furthermore, PSMA PET consistently led to a shift in clinical management, thus increasing the proportion of radiotherapy, surgery, or other focal therapies at the expense of systemic options or no treatment. In oligometastatic disease after radical surgery, PSMA PET may be relevant in guiding a metastasis-directed therapy approach, as preliminary data seem to suggest a benefit in terms of progression-free survival after treatment of PSMA PET-positive lesions. As a staging and gatekeeping technique, PSMA PET represents a reliable whole-body imaging procedure in combination with second-line therapy of castration-resistant PCa, as well as being pivotal when assessing patients eligible for radioligand therapy such as ¹⁷⁷Lu-PSMA. This critical review aims at providing a comprehensive overview of the latest literature on the current or emerging main indications, as well as a general outlook on the recommended interpretation criteria for PSMA PET imaging.

Prostate-Specific Membrane Antigen Uptake and Survival in Metastatic Castration-Resistant Prostate Cancer

Background

Prostate-specific membrane antigen (PSMA) imaging has been suggested as highly sensitive modality for detection of metastases in patients with biochemically recurrent or advanced prostate cancer (PCa). PSMA expression is associated with grade and stage and has a relationship with androgen receptor signaling. The aim of this study was to evaluate the prognostic utility of radiographic PSMA expression in men with metastatic castration-resistant prostate cancer (mCRPC).

Methods

Patients with mCRPC and available baseline PSMA imaging were studied. Images by planar/single-photon emission computed tomography (SPECT) or positron emission tomography (PET)/CT were reviewed. Planar/SPECT images were scored semi-quantitatively and PET/CT scored quantitatively with comparison of tumor uptake to liver uptake on a scale of 0–4 in order to determine an imaging score (IS). The IS (high: 2–4 versus low: 0–1), subsequent receipt of life-prolonging systemic therapies (taxane chemotherapy, potent androgen receptor pathway inhibitors, sipuleucel-T, and radium-223), and the CALGB prognostic risk stratification of patients were analyzed according to overall survival (OS) in univariate and multivariate Cox’s proportional hazards models.

Results

High PSMA expression (IS 2–4) was found in 179 (75.21%) patients, and 59 (24.79%) patients had low PSMA uptake. The median OS of the entire cohort was 16.8 (95%CI: 14.9–19.3) months. Patients with a high IS had a significantly shorter OS of 15.8 (95%CI 13.0–18.1) months compared to those with low expression [22.7 (95%CI: 17.7–30.7) months, p = 0.002]. After accounting for use of life-prolonging therapies (p<0.001) and CALGB prognostic groups (p = 0.001), high PSMA IS emerged as an independent prognostic factor for OS [HR(95%CI): 1.7 (1.2–2.2); p = 0.003].

Conclusion

Presence of high radiographic PSMA expression on SPECT or PET/CT may portend a poor prognosis in patients with mCRPC treated with standard systemic therapies. This provides implications for therapeutic targeting of PSMA-avid disease as a means to improve outcomes.

Molecular imaging and biochemical response assessment after a single cycle of [225Ac]Ac-PSMA-617/[177Lu]Lu-PSMA-617 tandem therapy in mCRPC patients who have progressed on [177Lu]Lu-PSMA-617 monotherapy

Rationale: Despite the promising results of prostate-specific membrane antigen (PSMA)-targeted ¹⁷⁷Lu radioligand therapy in metastatic castration-resistant prostate carcinoma (mCRPC), some patients do not respond and other patients with initially good response develop resistance to this treatment. In this study, we investigated molecular imaging and biochemical responses after a single cycle of [²²⁵Ac]Ac-PSMA-617/[¹⁷⁷Lu]Lu-PSMA-617 tandem therapy in patients who had progressed on [¹⁷⁷Lu]Lu-PSMA-617 monotherapy.

Methods: Seventeen patients with mCRPC were included in a retrospective, monocenter study. Molecular imaging-based response was assessed by modified PERCIST criteria using the whole-body total lesion PSMA (TLP) and molecular tumour volume (MTV) derived from [⁶⁸Ga]Ga-PSMA-11 PET/CT. Biochemical response was evaluated according to PCWG3 criteria using the prostate-specific antigen (PSA) serum value. Concordance and correlation statistics as well as survival analyses were performed.

Results: Based on the molecular imaging-based response assessment, 5 (29.4%) patients showed partial remission and 7 (41.2%) had stable disease. The remaining 5 (29.4%) patients had further progression, four with an increase in TLP/MTV of >30% and one with stable TLP/MTV but appearance of new metastases. Based on the biochemical response assessment, 5 (29.4%), 8 (47.1%), and 4 (23.5%) patients showed partial remission, stable disease, and progressive disease, respectively. A comparison of the response assessment methods showed a concordance of 100% (17/17) between TLP and MTV and 70.6% (12/17) between TLP/MTV and PSA. Patients with partial remission, independently assessed by each method, had better overall survival (OS) than patients with either stable or progressive disease. The difference in OS was statistically significant for the molecular imaging response assessment (median OS not reached vs. 8.3 m, p = 0.044), but not for the biochemical response assessment (median OS 18.1 m vs. 9.4 m, p = 0.468).

Conclusion: Based on both assessment methods, [²²⁵Ac]Ac-PSMA-617/[¹⁷⁷Lu]Lu-PSMA-617 tandem therapy is an effective treatment for the highly challenging cohort of patients with mCRPC who have progressed on [¹⁷⁷Lu]Lu-PSMA-617 monotherapy. Molecular imaging response and biochemical PSA response were mostly concordant, though a considerable number of cases (29.4%) were discordant. Molecular imaging response reflecting the change in total viable tumour burden appears to be superior to PSA change in estimating survival outcome after tandem therapy.

Prostate-specific Membrane Antigen-based Imaging of Castration-resistant Prostate Cancer

CONTEXT

Positron emission tomography (PET) targeting prostate-specific membrane antigen (PSMA) has unprecedented accuracy for localization of initial or recurrent prostate cancer (PC). There is now growing evidence regarding the value of PSMA-PET in patients with advanced PC.

OBJECTIVE

To review the value of PSMA-PET/computed tomography (CT) in the context of castration-resistant PC (CRPC).

EVIDENCE ACQUISITION

A search of the PubMed database using the terms "PSMA PET castration resistant prostate cancer" (years 2011-2020) was performed. Reviews, case reports/series, non-English articles, preclinical studies, access-restricted studies, and studies on PSMA radioligand therapy without further analysis of PSMA-PET parameters were subsequently excluded.

EVIDENCE SYNTHESIS

Compared to conventional imaging, PSMA-PET better identifies the true extent of CRPC, especially nonmetastatic CRPC. The clinical benefit of this stage migration is still unclear and needs to be evaluated in further studies. High accuracy of PSMA-PET holds promise for better, PET-guided metastasis-directed treatment in patients with oligometastatic CRPC. PSMA-PET is an essential eligibility criterion for [¹⁷⁷Lu]-PSMA theranostic applications. Preliminary evidence indicates the value of PSMA-PET for the assessment of treatment responses.

CONCLUSIONS

Among other applications, PSMA-PET offers more precise staging for nonmetastatic CRPC. In particular, target localization for metastasis-directed therapy and target expression assessment for PSMA radioligand therapy also hold promise. Potential translation of this diagnostic tool into an oncologic benefit needs to be defined in future trials.

PATIENT SUMMARY

This review describes how prostate-specific membrane antigen positron emission tomography (PSMA-PET), a new sensitive imaging tool for prostate cancer, might help to guide clinicians in making treatment decisions for advanced prostate cancer.

Imaging for Response Assessment in Cancer Clinical Trials

The use of biomarkers is integral to the routine management of cancer patients, including diagnosis of disease, clinical staging and response to therapeutic intervention. Advanced imaging metrics with computed tomography (CT), magnetic resonance imaging (MRI), and positron emission tomography (PET) are used to assess response during new drug development and in cancer research for predictive metrics of response. Key components and challenges to identifying an appropriate imaging biomarker are selection of integral vs integrated biomarkers, choosing an appropriate endpoint and modality, and standardization of the imaging biomarkers for cooperative and multicenter trials. Imaging biomarkers lean on the original proposed quantified metrics derived from imaging such as tumor size or longest dimension, with the most commonly implemented metrics in clinical trials coming from the Response Evaluation Criteria in Solid Tumors (RECIST) criteria, and then adapted versions such as immune-RECIST (iRECIST) and Positron Emission Tomography Response Criteria in Solid Tumors (PERCIST) for immunotherapy response and PET imaging, respectively. There have been many widely adopted biomarkers in clinical trials derived from MRI including metrics that describe cellularity and vascularity from diffusion-weighted (DW)-MRI apparent diffusion coefficient (ADC) and Dynamic Susceptibility Contrast (DSC) or dynamic contrast enhanced (DCE)-MRI (Ktrans, relative cerebral blood volume (rCBV)), respectively. Furthermore, Fluorodexoyglucose (FDG), fluorothymidine (FLT), and fluoromisonidazole (FMISO)-PET imaging, which describe molecular markers of glucose metabolism, proliferation and hypoxia have been implemented into various cancer types to assess therapeutic response to a wide variety of targeted- and chemotherapies. Recently, there have been many functional and molecular novel imaging biomarkers that are being developed that are rapidly being integrated into clinical trials (with anticipation of being implemented into clinical workflow in the future), such as artificial intelligence (AI) and machine learning computational strategies, antibody and peptide specific molecular imaging, and advanced diffusion MRI. These include prostate-specific membrane antigen (PSMA) and trastuzumab-PET, vascular tumor burden extracted from contrast-enhanced CT, diffusion kurtosis imaging, and CD8 or Granzyme B PET imaging. Further excitement surrounds theranostic procedures such as the combination of 68Ga/111In- and 177Lu-DOTATATE to use integral biomarkers to direct care and personalize therapy. However, there are many challenges in the implementation of imaging biomarkers that remains, including understand the accuracy, repeatability and reproducibility of both acquisition and analysis of these imaging biomarkers. Despite the challenges associated with the biological and technical validation of novel imaging biomarkers, a distinct roadmap has been created that is being implemented into many clinical trials to advance the development and implementation to create specific and sensitive novel imaging biomarkers of therapeutic response to continue to transform medical oncology.

Prediction of response and survival after standardized treatment with 7400 MBq 177Lu-PSMA-617 every 4 weeks in patients with metastatic castration-resistant prostate cancer

BACKGROUND AND AIMS

[¹⁷⁷Lu]Lu-PSMA-617 radioligand therapy (PSMA-RLT) is a new therapy for patients with metastatic castration-resistant prostate cancer (mCRPC). However, identification of reliable prognostic factors is hampered by heterogeneous treatment regimens applied in previous studies. Hence, we sought clinical factors able to predict response and survival to PSMA-RLT in a homogenous group of patients, all receiving 7400 MBq every 4 weeks.

PATIENTS AND METHODS

Data of 61 patients (mean age 71.6 ± 6.9 years, median basal PSA 70.7 [range 1.0-4890 μg/L]), pretreated with abiraterone/enzalutamide (75.4%) and docetaxel/cabazitaxel (68.9%), received three cycles of PSMA-RLT (mean 7321 ± 592 MBq) at four weekly intervals and were analyzed retrospectively. General medical conditions and laboratory parameters of every patients were regularly assessed. Response to therapy was based on PSA levels 1 month after the 3rd cycle. Binary logistic regression test and Kaplan-Meier estimates were used to evaluate predictors and overall survival (OS).

RESULTS

Forty-nine (80.3%) patients demonstrated a therapy response in terms of any PSA decline, while 21 (19.7%) patients showed increase or no changes in their PSA levels. Baseline hemoglobin (Hb) significantly predicted PSA reductions of ≥ 50% 4 weeks after receiving the 3rd PSMA-RLT (P = 0.01, 95% CI: 1.09-2.09) with an AUC of 0.68 (95% CI: 0.54-0.81). The levels of basal Hb and basal PSA were able to predict survival of patients, both P < 0.05 (relative risk 1.51 and 0.79, 95% CI: 1.09-2.09 and 0.43-1.46), respectively. In comparison to patients with reduced basal Hb, patients with normal basal Hb levels lived significantly longer (median survival not reached vs. 89 weeks, P = 0.016). Also, patients with basal PSA levels ≤ 650 μg/L had a significantly longer survival than patients with basal PSA levels > 650 μg/L (median survival not reached vs. 97 weeks, P = 0.031). Neither pretreatments with abiraterone/enzalutamide or docetaxel/cabazitaxel nor distribution of metastasis affected survival and rate of response to PSMA-RLT.

CONCLUSION

Basal Hb level is an independent predictor for therapy response and survival in patients receiving PSMA-RLT every 4 weeks. Both baseline PSA ≤ 650 μg/L and normal Hb levels were associated with longer survival.

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.

Prostate-specific Membrane Antigen PET: Therapy Response Assessment in Metastatic Prostate Cancer

Therapy response assessment is a critical step in cancer management, leading clinicians to optimize the use of therapeutic options during the course of the disease. Imaging is a pivotal biomarker for therapy response evaluation in oncology and has gained wider use through the development of reproducible data-based guidelines, of which the Response Evaluation Criteria in Solid Tumors is the most successful example. Disease-specific criteria have also been proposed, and the Prostate Cancer Working Group 3 criteria are the mainstay for prostate cancer (PC). However, conventional imaging evaluation in metastatic PC has several limitations, including (a) the inability to detect small-volume disease, (b) the high prevalence of bone (nonmeasurable) lesions at imaging, and (c) the established role of serum prostate-specific antigen (PSA) levels as the biomarker of choice for response assessment and disease progression. In addition, there are an increasing number of newer treatment options with various effects on imaging features. Prostate-specific membrane antigen (PSMA) PET has improved patient selection for newer treatments, such as metastasis-directed therapy (MDT) or radionuclide therapy. The role of PSMA PET in response assessment for many metastatic PC therapeutic options (MDT, androgen deprivation therapy, chemotherapy, radionuclide therapy, and immunotherapy) is an evolving issue, with emerging data showing good correlation with PSA levels and clinical outcome. However, there are specific implications of each therapy (especially androgen deprivation therapy and immunotherapy) on PSMA expression by PC cells, leading to potential pitfalls and inaccuracies that must be known by radiologists. Despite some limitations, PSMA PET is addressing gaps left by conventional imaging methods (eg, CT and bone scanning) and nonimaging biomarkers (PSA levels) in metastatic PC therapy response assessment, a role that can be improved with advances like refinement of interpretation criteria and whole-body tumor burden quantification.^© RSNA, 2020See discussion on this article by Barwick and Castellucci.

Semiautomatically Quantified Tumor Volume Using 68Ga-PSMA-11 PET as a Biomarker for Survival in Patients with Advanced Prostate Cancer

Prostate-specific membrane antigen (PSMA)-targeting PET imaging is becoming the reference standard for prostate cancer staging, especially in advanced disease. Yet, the implications of PSMA PET-derived whole-body tumor volume for overall survival are poorly elucidated to date. This might be because semiautomated quantification of whole-body tumor volume as a PSMA PET biomarker is an unmet clinical challenge. Therefore, in the present study we propose and evaluate a software that enables the semiautomated quantification of PSMA PET biomarkers such as whole-body tumor volume. Methods: The proposed quantification is implemented as a research prototype. PSMA-accumulating foci were automatically segmented by a percental threshold (50% of local SUV_max). Neural networks were trained to segment organs in PET/CT acquisitions (training CTs: 8,632, validation CTs: 53). Thereby, PSMA foci within organs of physiologic PSMA uptake were semiautomatically excluded from the analysis. Pretherapeutic PSMA PET/CTs of 40 consecutive patients treated with ¹⁷⁷Lu-PSMA-617 were evaluated in this analysis. The whole-body tumor volume (PSMA_TV50), SUV_max, SUV_mean, and other whole-body imaging biomarkers were calculated for each patient. Semiautomatically derived results were compared with manual readings in a subcohort (by 1 nuclear medicine physician). Additionally, an interobserver evaluation of the semiautomated approach was performed in a subcohort (by 2 nuclear medicine physicians). Results: Manually and semiautomatically derived PSMA metrics were highly correlated (PSMA_TV50: R ² = 1.000, P < 0.001; SUV_max: R ² = 0.988, P < 0.001). The interobserver agreement of the semiautomated workflow was also high (PSMA_TV50: R ² = 1.000, P < 0.001, interclass correlation coefficient = 1.000; SUV_max: R ² = 0.988, P < 0.001, interclass correlation coefficient = 0.997). PSMA_TV50 (ml) was a significant predictor of overall survival (hazard ratio: 1.004; 95% confidence interval: 1.001-1.006, P = 0.002) and remained so in a multivariate regression including other biomarkers (hazard ratio: 1.004; 95% confidence interval: 1.001-1.006 P = 0.004). Conclusion: PSMA_TV50 is a promising PSMA PET biomarker that is reproducible and easily quantified by the proposed semiautomated software. Moreover, PSMA_TV50 is a significant predictor of overall survival in patients with advanced prostate cancer who receive ¹⁷⁷Lu-PSMA-617 therapy.