The effect of androgen deprivation therapy on 68Ga-PSMA tracer uptake in non-metastatic prostate cancer patients

Evolving Paradigms in Prostate Cancer: The Integral Role of Prostate-Specific Membrane Antigen Positron Emission Tomography/Computed Tomography in Primary Staging and Therapeutic Decision-Making

Prostate-specific membrane antigen (PSMA) positron emission tomography or computed tomography (PET/CT) has emerged as a superior imaging option to conventional imaging for prostate cancer. The majority of early evidence and prospective trials evaluated PSMA PET/CT in the biochemical recurrence or metastatic setting. However, there has been an increasing number of prospective trials in the primary setting. The purpose of this narrative review was to describe the role of PSMA PET/CT in localized primary prostate cancer. This narrative review focuses on the prospective evidence available in this setting. We detail the current practice and future potential for PSMA PET/CT to be used in multiple stages of localized primary prostate cancer. The most common practice currently for PSMA PET/CT is in the primary nodal and metastatic staging of high-risk prostate cancer. We describe other roles of PSMA PET/CT, including in intermediate-risk prostate cancer as well as local staging and the impact on radiation therapy and surgical management. We also discuss the potential future roles of PSMA PET/CT in prediagnosis such as risk stratification for biopsy, prognosis, and specific surgical roles. Potential pitfalls of PSMA PET/CT are also addressed. PSMA PET/CT has already had a significant influence on prostate cancer, and there will continue to be a greater role for this imaging modality in localized primary prostate cancer.

Prostate-Specific Membrane Antigen PET Response Associates with Metastasis-Free Survival After Stereotactic Ablative Radiation in Oligometastatic Prostate Cancer

Purpose

Emerging data suggest that metastasis-directed therapy (MDT) improves outcomes in patients with oligometastatic castration-sensitive prostate cancer (omCSPC). Prostate-specific membrane antigen positron emission tomography (PSMA-PET) can detect occult metastatic disease, and PSMA response has been proposed as a biomarker for treatment response. Herein, we identify and validate a PSMA-PET biomarker for metastasis-free survival (MFS) following MDT in omCSPC.

Methods and Materials

We performed an international multi-institutional retrospective study of patients with omCSPC, defined as ≤3 lesions, treated with metastasis-directed stereotactic ablative radiation who underwent PSMA-PET/computed tomography (CT) before and after (median, 6.2 months; range, 2.4-10.9 months) treatment. Pre- and post-MDT PSMA-PET/CT maximum standardized uptake value (SUVmax) was measured for all lesions, and PSMA response was defined as the percent change in SUVmax of the least responsive lesion. PSMA response was both evaluated as a continuous variable and dichotomized into PSMA responders, with a complete/partial response (at least a 30% reduction in SUVmax), and PSMA nonresponders, with stable/progressive disease (less than a 30% reduction in SUVmax). PSMA response was correlated with conventional imaging-defined metastasis-free survival (MFS) via Kaplan-Meier and Cox regression analysis.

Results

A total of 131 patients with 261 treated metastases were included in the analysis, with a median follow-up of 29 months (IQR, 18.5-41.3 months). After stereotactic ablative radiation, 70.2% of patients were classified as PSMA responders. Multivariable analysis demonstrated that PSMA response as a continuous variable was associated with a significantly worse MFS (hazard ratio = 1.003; 95% CI, 1.001-1.006; P = .016). Patients classified as PSMA responders were found to have a significantly improved median MFS of 39.9 versus 12 months (P = .001) compared with PSMA nonresponders. Our study is limited as it is a retrospective review of a heterogenous population.

Conclusions

After stereotactic ablative radiation, PSMA-PET response appears to be a radiographic biomarker that correlates with MFS in omCSPC. This approach holds promise for guiding clinical management of omCSPC and should be validated in a prospective setting.

Treatment Response Imaging in Prostate Cancer

Objective criteria for measuring treatment response in prostate cancer are critical to clinical research and practice. The Prostate Cancer Working Group 3 criteria are widely accepted relying only on conventional imaging for radiographic treatment response. Prostate-specific membrane antigen PET/computed tomography was proven to be superior to conventional imaging in initial diagnosis and biochemical recurrence of prostate cancer. Moreover, there is growing evidence of its role in treatment response assessment in prostate cancer. This study will review the different criteria for imaging treatment response on conventional and advanced molecular imaging for different therapies, and the future perspective in posttherapy imaging.

Robustness of magnetic resonance imaging and positron emission tomography radiomic features in prostate cancer: Impact on recurrence prediction after radiation therapy

Background and purpose

Radiomic features from MRI and PET are an emerging tool with potential to improve prostate cancer outcomes. However, feature robustness due to image segmentation variations is currently unknown. Therefore, this study aimed to evaluate the robustness of radiomic features with segmentation variations and their impact on predicting biochemical recurrence (BCR).

Materials and methods

Multi-scanner, pre-radiation therapy imaging from 142 patients with localised prostate cancer was used. Imaging included T2-weighted (T2), apparent diffusion coefficient (ADC) MRI, and prostate-specific membrane antigen (PSMA)-PET. The prostate gland and intraprostatic tumours were manually and automatically segmented, and differences were quantified using Dice Coefficient (DC). Radiomic features including shape, first-order, and texture features were extracted for each segmentation from original and filtered images. Intraclass Correlation Coefficient (ICC) and Mean Absolute Percentage Difference (MAPD) were used to assess feature robustness. Random forest (RF) models were developed for each segmentation using robust features to predict BCR.

Results

Prostate gland segmentations were more consistent (mean DC = 0.78) than tumour segmentations (mean DC = 0.46). 112 (3.6 %) radiomic features demonstrated 'excellent' robustness (ICC > 0.9 and MAPD < 1 %), and 480 features (15.4 %) demonstrated 'good' robustness (ICC > 0.75 and MAPD < 5 %). PET imaging provided more features with excellent robustness than T2 and ADC. RF models showed strong predictive power for BCR with a mean area under the receiver-operator-characteristics curve (AUC) of 0.89 (range 0.85-0.93).

Conclusion

When using radiomic features for predictive modelling, segmentation variability should be considered. To develop BCR predictive models, radiomic features from the entire prostate gland are preferable over tumour segmentation-based features.

PSMA PET imaging in the diagnosis and management of prostate cancer

Prostate cancer is the second leading cause of cancer-related deaths in men in the United States. Imaging techniques such as CT, MRI, and bone scans have traditionally been used for diagnosis and staging. Molecular imaging modalities targeting the prostate-specific membrane antigen (PSMA) have recently gained attention due to their high affinity and accuracy. PSMA PET has been combined with other modalities such as multiparametric MRI for better diagnostic and prognostic performance. PSMA imaging has been studied at different clinical settings with a wide range of disease aggressiveness. In this review we will explore the role of PSMA PET in high-risk prostate cancer staging, biochemical recurrence, and castration-resistant prostate cancer. The primary focus of this review article is to examine the latest developments in the use of PSMA imaging and emphasize the clinical situations where its effectiveness has been demonstrated to significantly impact the treatment of prostate cancer. In addition, we will touch upon the potential future advancements of PSMA PET imaging and its evolving significance in the management of prostate cancer.

Associations of quantitative whole-body PSMA-PET metrics with PSA progression status under long-term androgen deprivation therapy in prostate cancer patients: a retrospective single-center study

PURPOSE

To evaluate whether quantitative whole-body (WB) PSMA-PET metrics under long-term androgen deprivation therapy (ADT) and/or androgen receptor signaling inhibitors (ARSi) are associated with PSA progression.

METHODS

Patients who underwent at least 2 68Ga-PSMA-11 PET/CT scans between October 2016 and April 2021 (n = 372) and started a new line of ADT ± ARSi between PET1 and PET2 were retrospectively screened for inclusion. We investigated the association between PCWG3-defined PSA progression status at PET2 and the following PSMA-PET parameters: appearance of new lesions on PET2, ≥ 20% increase in WB-PSMA tumor volume (WB-PSMA-VOL), progression of disease (PD) by RECIP 1.0, and ≥ 30% increase in WB-PSMA-SUVmean from PET1 to PET2. Spearman's rank correlation coefficients and Fisher's exact test were used to evaluate the associations.

RESULTS

Thirty-five patients were included: 12/35 (34%) were treated with ADT only and 23/35 (66%) with ARSi ± ADT. The median time between PET1 and PET2 was 539 days. Changes (%) in median PSA levels, WB-PSMA-SUVmean, and WB-PSMA-VOL from PET1 to PET2 were -86%, -23%, and -86%, respectively. WB-PSMA-VOL ≥ 20%, new lesions, RECIP-PD, and WB-PSMA-SUVmean ≥ 30% were observed in 5/35 (14%), 9/35 (26%), 5/35 (14%), and 4/35 (11%) of the whole cohort, in 3/9 (33%), 7/9 (78%), 3/9 (33%), and 2/9 (22%) of patients with PSA progression at PET2, and in 2/26 (8%), 2/26 (8%), 2/26 (8%), and 2/26 (8%) of patients without PSA progression at PET2 (p = 0.058, p < 0.001, p = 0.058, p = 0.238, respectively). Changes in PSA were correlated to percent changes in WB-PSMA-VOL and WB-PSMA-SUVmean (Spearman ρ: 0.765 and 0.633, respectively; p < 0.001).

CONCLUSION

Changes in PSA correlated with changes observed on PSMA-PET, although discordance between PSA and PSMA-PET changes was observed. Further research is necessary to evaluate if PSMA-PET parameters can predict progression-free survival and overall survival and serve as novel endpoints in clinical trials.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSION

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

The Association Between [68Ga]PSMA PET/CT Response and Biochemical Progression in Patients with High-Risk Prostate Cancer Receiving Neoadjuvant Therapy

Our previous study found that the prostate-specific membrane antigen (PSMA) PET/CT response of primary prostate cancer (PCa) to neoadjuvant therapy can predict the pathologic response. This study was designed to investigate the association between [68Ga]PSMA PET/CT changes and biochemical progression-free survival (bPFS) in high-risk patients who underwent neoadjuvant therapy before radical prostatectomy (RP). Methods: Seventy-five patients with high-risk PCa in 2 phase II clinical trials who received neoadjuvant therapy before RP were included. The patients received androgen deprivation therapy plus docetaxel (n = 33) or androgen deprivation therapy plus abiraterone (n = 42) as neoadjuvant treatment. All patients had serial [68Ga]PSMA PET/CT scans before and after neoadjuvant therapy. Age, initial prostate-specific antigen level, nadir prostate-specific antigen level before RP, tumor grade at biopsy, treatment regimen, clinical T stage, PET imaging features, pathologic N stage, and pathologic response on final pathology were included for univariate and multivariate Cox regression analyses to identify independent predictors of bPFS. Results: With a median follow-up of 30 mo, 18 patients (24%) experienced biochemical progression. Multivariate Cox regression analyses revealed that only SUVmax derived from posttreatment [68Ga]PSMA PET/CT and pathologic response on final pathology were independent factors for the prediction of bPFS, with hazard ratios of 1.02 (95% CI, 1.00-1.04; P = 0.02) and 0.12 (95% CI, 0.02-0.98; P = 0.048), respectively. Kaplan-Meier analysis revealed that patients with a favorable [68Ga]PSMA PET/CT response (posttreatment SUVmax < 8.5) or a favorable pathologic response (pathologic complete response or minimal residual disease) had a significantly lower rate of 3-y biochemical progression. Conclusion: Our results indicated that [68Ga]PSMA PET/CT response was an independent risk factor for the prediction of bPFS in patients with high-risk PCa receiving neoadjuvant therapy and RP, suggesting [68Ga]PSMA PET/CT to be an ideal tool to monitor response to neoadjuvant therapy.

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.

A Review of Modern Imaging Landscape for Prostate Cancer: A Comprehensive Clinical Guide

The development of prostate cancer imaging is rapidly evolving, with many changes to the way patients are diagnosed, staged, and monitored for recurrence following treatment. New developments, including the potential role of imaging in screening and the combined diagnostic and therapeutic applications in the field of theranostics, are underway. In this paper, we aim to outline the current landscape in prostate cancer imaging and look to the future at the potential modalities and applications to come.

68Ga-PSMA-11 PET/CT Features Extracted from Different Radiomic Zones Predict Response to Androgen Deprivation Therapy in Patients with Advanced Prostate Cancer

Purpose: Prediction of treatment response to androgen deprivation therapy (ADT) prior to treatment initiation remains difficult. This study was undertaken to investigate whether 68Ga-PSMA-11 PET/CT features extracted from different radiomic zones within the prostate gland might predict response to ADT in patients with advanced prostate cancer (PCa). Methods: A total of 35 patients with prostate adenocarcinoma underwent two 68Ga-PSMA-11 PET/CT scans—termed PET-1 and PET-2—before and after 3 months of ADT, respectively. The prostate was divided into three radiomic zones, with zone-1 being the metabolic tumor zone, zone-2 the proximal peripheral tumor zone, and zone-3 the extended peripheral tumor zone. Patients in the response group were those who showed a reduction ratio > 30% for PET-derived parameters measured at PET-1 and PET-2. The remaining patients were classified as non-responders. Results: Seven features (glcm_idmn, glcm_idn, glcm_imc1, ngtdm_Contrast, glrlm_rln, gldm_dn, and shape_MeshVolume) from zone-1, two features (gldm_sdlgle and shape_MinorAxisLength) from zone-2, and two features (diagnostics_Mask-interpolated_Minimum and shape_Sphericity) from zone-3 successfully distinguished responders from non-responders to ADT. One predictive feature (shape_SurfaceVolumeRatio) was consistently identified in all of the three zones. Conclusions: this study demonstrates the potential usefulness of radiomic features extracted from different prostatic zones in distinguishing responders from non-responders prior to ADT initiation.

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.

The Role of PSMA PET/CT in the Primary Diagnosis and Follow-Up of Prostate Cancer-A Practical Clinical Review

Simple Summary

The combination of positron emission tomography (PET)-diagnostics with ligands binding to the prostate-specific membrane antigen (PSMA) has been a diagnostic milestone in the situation of biochemical recurrence of prostate cancer and is gaining importance in primary diagnostics, providing a highly specific and sensitive diagnostic method in various clinical situations. However, the clinical application of this method requires a comprehensive knowledge of its advantages and disadvantages, potential pitfalls and influencing factors. This review aims to provide a practical clinical review of the currently available background data on PSMA PET/CT, as well as the clinical implications. Although a large amount of data already exist, a thorough analysis is complicated by study heterogeneity, showing the need for future systematic and prospective research.

Abstract

The importance of PSMA PET/CT in both primary diagnostics and prostate cancer recurrence has grown steadily since its introduction more than a decade ago. Over the past years, a vast amount of data have been published on the diagnostic accuracy and the impact of PSMA PET/CT on patient management. Nevertheless, a large heterogeneity between studies has made reaching a consensus difficult; this review aims to provide a comprehensive clinical review of the available scientific literature, covering the currently known data on physiological and pathological PSMA expression, influencing factors, the differences and pitfalls of various tracers, as well as the clinical implications in initial TNM-staging and in the situation of biochemical recurrence. This review has the objective of providing a practical clinical overview of the advantages and disadvantages of the examination in various clinical situations and the body of knowledge available, as well as open questions still requiring further research.

PET-CT in Clinical Adult Oncology-IV. Gynecologic and Genitourinary Malignancies

Simple Summary

Positron emission tomography (PET), typically combined with computed tomography (CT), has become a critical advanced imaging technique in oncology. With concurrently acquired positron emission tomography and computed tomography (PET-CT), a radioactive molecule (radiotracer) is injected in the bloodstream and localizes to sites of tumor because of specific cellular features of the tumor that accumulate the targeting radiotracer. The CT scan provides information to allow better visualization of radioactivity from deep or dense structures and to provide detailed anatomic information. PET-CT has a variety of applications in oncology, including staging, therapeutic response assessment, restaging and surveillance. This series of six review articles provides an overview of the value, applications, and imaging interpretive strategies for PET-CT in the more common adult malignancies. The fourth report in this series provides a review of PET-CT imaging in gynecologic and genitourinary malignancies.

Abstract

Concurrently acquired positron emission tomography and computed tomography (PET-CT) is an advanced imaging modality with diverse oncologic applications, including staging, therapeutic assessment, restaging and longitudinal surveillance. This series of six review articles focuses on providing practical information to providers and imaging professionals regarding the best use and interpretative strategies of PET-CT for oncologic indications in adult patients. In this fourth article of the series, the more common gynecological and adult genitourinary malignancies encountered in clinical practice are addressed, with an emphasis on Food and Drug Administration (FDA)-approved and clinically available radiopharmaceuticals. The advent of new FDA-approved radiopharmaceuticals for prostate cancer imaging has revolutionized PET-CT imaging in this important disease, and these are addressed in this report. However, [¹⁸F]F-fluoro-2-deoxy-d-glucose (FDG) remains the mainstay for PET-CT imaging of gynecologic and many other genitourinary malignancies. This information will serve as a guide for the appropriate role of PET-CT in the clinical management of gynecologic and genitourinary cancer patients for health care professionals caring for adult cancer patients. It also addresses the nuances and provides guidance in the accurate interpretation of FDG PET-CT in gynecological and genitourinary malignancies for imaging providers, including radiologists, nuclear medicine physicians and their trainees.

Molecular Imaging Assessment of Androgen Deprivation Therapy in Prostate Cancer

Hormonal therapy has long been recognized as a mainstay treatment for prostate cancer. New generation imaging agents have provided unprecedented opportunities at all phases along the natural history of prostate cancer. We review the literature on the effect of androgens and androgen deprivation therapy on prostate tumor at its various biological phases using the new generation molecular imaging agents in conjunction with positron emission tomography.

Impact of Three-Month Androgen Deprivation Therapy on [68Ga]Ga-PSMA-11 PET/CT Indices in Men with Advanced Prostate Cancer-Results from a Pilot Prospective Study

Purpose: The purpose of this pilot prospective study is to examine the gallium-68-prostate-specific membrane antigen-11 ([68Ga]Ga-PSMA-11) positron emission tomography/computed tomography (PET/CT) imaging response in patients with advanced or metastatic hormone-naïve prostate cancer (PC) after 3 months of androgen deprivation therapy (ADT). Methods: We prospectively included men with untreated, clinical stage III or IV PC scheduled to receive ADT for at least 6 months. [68Ga]Ga-PSMA-11 PET/CT images were obtained before the start of ADT and 10−14 weeks thereafter. The following indices were examined: maximum standardized uptake value (SUVmax), mean SUV, PSMA total volume, and PSMA total lesion values of the prostate, nodes, bones, and whole-body. The therapeutic response was assessed using the modified PET response criteria in solid tumors 1.0. A subgroup analysis of patients with the International Society of Urological Pathology (ISUP) grade group 5 versus <5 was also performed. Results: A total of 30 patients were eligible. All PSMA PET/CT indices were significantly reduced (p < 0.001) after 3 months of ADT. Twenty-four (80%) patients showed partial response. Complete response, stable disease, and disease progression were observed in two patients each. Sixteen patients with ISUP grade group 5 showed a less prominent SUVmax reduction (p = 0.006), and none of them reached complete response. Conclusions: Three months of ADT in patients with untreated, advanced PC significantly reduced PSMA PET/CT indices. While most participants partially responded to ADT, patients with ISUP grade group 5 showed a less prominent SUVmax reduction. Collectively, our pilot results indicate that [68Ga]Ga-PSMA-11 PET/CT imaging holds promise to monitor treatment response after the first three months of ADT.

Nonmetastatic Castration-Resistant Prostate Cancer: Current Challenges and Trends

Prostate carcinoma is a highly prevalent biologically and clinically diverse disease, generally associated with a consistent elevation of prostate-specific antigen levels. Castration-resistant prostate cancer represents a heterogeneous clinical setting that ranges from patients with an asymptomatic prostate-specific antigen elevation after hormone blockade failure and good performance status to patients with significant debilitating symptoms and rapidly progressive disease, leading to death. Nonmetastatic castration-resistant prostate cancer is a transient disease stage defined over specific criteria established within a sensitive time period. The majority of the patients with nonmetastatic castration-resistant prostate cancer will eventually develop metastatic lesions, associated with prostate cancer-specific morbidity and mortality. However, progression to metastatic disease is a heterogeneous process still not fully understood, with studies suggesting that younger age, high Gleason score (> 7), high prostate-specific antigen levels, reduced prostate-specific antigen doubling time (< 6 months), and a rapid alkaline phosphatase rise as potentially associated factors. Although the nonmetastatic castration-resistant prostate cancer treatment landscape has substantially evolved in recent years, the disease heterogeneity makes treatment decisions for this population challenging in the effort to achieve a balance between the risk of disease progression and the toxicity of new treatments in patients who often have associated comorbidities, yet are generally asymptomatic. The present article addresses the current main challenges in nonmetastatic castration-resistant prostate cancer management, including in diagnosis, owing to the development of new imaging modalities with a direct impact in disease detection, prognostic classification, as a result of the traditionally oversimplified definition of disease aggressiveness (mainly based on prostate-specific antigen doubling time), and patient selection for the most adequate treatment.

Monitoring PSMA Responses to ADT in Prostate Cancer Patient-Derived Xenograft Mouse Models Using [18F]DCFPyL PET Imaging

PURPOSE

PSMA overexpression has been associated with aggressive prostate cancer (PCa). However, PSMA PET imaging has revealed highly variable changes in PSMA expression in response to ADT treatment ranging from increases to moderate decreases. To better understand these PSMA responses and potential relationship to progressive PCa, the PET imaging agent, [¹⁸F]DCFPyL, was used to assess changes in PSMA expression in response to ADT using genomically characterized LuCaP patient-derived xenograft mouse models (LuCaP-PDXs) which were found to be sensitive to ADT (LuCaP73 and LuCaP136;CS) or resistant (LuCaP167;CR).

METHODS

[¹⁸F]DCFPyL (2-(3-{1-carboxy-5-[(6-[¹⁸F]fluoro-pyridine-3-carbonyl)-amino]-pentyl}-ureido)-pentanedioic acid) was used to assess PSMA in vitro (saturation assays) in LuCaP tumor membrane homogenates and in vivo (imaging/biodistribution) in LuCaP-PDXs. Control and ADT-treated LuCaPs were imaged before ADT (0 days) and 2-, 7-, 14-, and 21-days post-ADT from which tumor:muscle ratios (T:Ms) were determined and concurrently tumor volumes were measured (caliper). After the 21-day imaging, biodistributions and histologic/genomic (PSMA, AR) analysis were done.

RESULTS

[¹⁸F]DCFPyL exhibited high affinity for PSMA and distinguished different levels of PSMA in LuCaP tumors. Post-ADT CS LuCaP73 and LuCaP136 tumor volumes significantly decreased at day 7 or 14 respectively vs controls, whereas the CR LuCaP167 tumor volumes were minimally changed. [¹⁸F]DCFPyL imaging T:Ms were increased 3-5-fold in treated LuCaP73 tumors vs controls, while treated LuCaP136 T:Ms remained unchanged which was confirmed by day 21 biodistribution results. For treated LuCaP167, T:Ms were decreased (~ 45 %) vs controls but due to low T:M values (<2) may not be indicative of PSMA level changes. LuCaP73 tumor PSMA histologic/genomic results were comparable to imaging/biodistribution results, whereas the results for other tumor types varied.

CONCLUSION

Tumor responses to ADT varied from sensitive to resistant among these LuCaP PDXs, while only the high PSMA expressing LuCaP model exhibited an increase in PSMA levels in response to ADT. These models may be useful in understanding the clinical relevance of PSMA PET responses to ADT and potentially the relationship to disease progression as it may relate to the genomic signature.

Utility of 18F-Fluciclovine PET/MRI for Staging Newly Diagnosed High-Risk Prostate Cancer and Evaluating Response to Initial Androgen Deprivation Therapy: A Prospective Single-Arm Pilot Study

BACKGROUND. Despite advances in prostate cancer treatment, rates of biochemical recurrence remain high, relating to lack of detection of small-volume metastatic disease using conventional imaging for initial staging. OBJECTIVE. The purpose of this study was to assess the potential use of 18F-fluciclovine PET/MRI for initial staging of high-risk prostate cancer and evaluating response to androgen deprivation therapy (ADT). METHODS. This prospective clinical trial enrolled 14 men with newly diagnosed high-risk prostate cancer and negative or equivocal conventional staging imaging for metastatic disease between January 2018 and February 2019. All patients underwent pretreatment 18F-fluciclovine PET/MRI including multiparametric prostate MRI; 12 underwent 18F-fluciclovine PET/MRI after surgery or between ADT and radiotherapy. Confidence in identification of the primary intraprostatic lesion and nodal metastases was independently rated on a 0-3 Likert scale by three readers with nuclear medicine experience for 18F-fluciclovine PET/MRI and three readers with abdominal imaging experience for MRI alone. Findings scored as 2 or 3 by at least two readers of a given modality were considered positive. A single reader measured SUVmean, SUVmax, and volume of the MRI-defined intraprostatic lesion and SUVmax of suspicious lymph nodes on PET before and after initiation of ADT. Changes in SUV were analyzed using nonparametric Wilcox-on signed-rank tests. RESULTS. The biopsy-proven lesion in the prostate gland was accurately identified in all 14 patients on both MRI and 18F-fluciclovine PET/MRI. Suspected nodal metastases were detected in three patients on MRI and seven patients on 18F-fluciclovine PET/MRI. After ADT, all patients showed decreased activity within the intraprostatic lesion and/or all suspicious lymph nodes. The primary lesion SUVmean was 4.5 ± 1.1 (range, 2.7-6.5) before treatment and 2.4 ± 1.1 (range, 0.0-3.6) after initiation of ADT (p = .008). For suspicious lymph nodes, the pretreatment SUVmax was 5.5 ± 3.7 (range, 2.8-12.7) and the post-treatment SUVmax was 2.8 ± 1.4 (range, 1.4-5.5) (p = .03). CONCLUSION.18F-labeled fluciclovine PET/MRI shows potential utility in initial staging of high-risk prostate cancer and in evaluating response to ADT. CLINICAL IMPACT. Given the FDA approval and widespread availability of 18F-fluciclovine, the findings could have an impact in the immediate future in guiding initial management of patients with prostate cancer. TRIAL REGISTRATION. ClinicalTrials.gov NCT03264456.

Correlation of Lesional Uptake Parameters and Ratios with miPSMA Score and Estimating Normal Physiologic Concentration: An Exploratory Analysis in Metastatic Castration-Resistant Prostatic Carcinoma Patients with 68Ga-PSMA-11 PET/CT

The use of prostate-specific membrane antigen (PSMA)-based PET/CT has grown rapidly in recent years. This study estimated lesional uptake, normal physiologic concentrations, and temporal variation on delayed PET/CT of ⁶⁸Ga-PSMA-11 across different molecular imaging PSMA (miPSMA) expression scores in patients with metastatic castration-resistant prostatic carcinoma. Methods: We retrospectively studied 50 patients who were evaluated for ¹⁷⁷Lu-PSMA-targeted radioligand therapy and underwent ⁶⁸Ga-PSMA-11 PET/CT to determine disease status. Their mean age was 67.5 ± 8 y (52-84 y), and their average serum prostate-specific antigen level was 401 ± 1,353 ng/mL (0.098-9,235.13 ng/mL) at the time of scanning. They underwent standard ⁶⁸Ga-PSMA-11 PET/CT an average of 65 min after injection (60-90 min). Tumors (n = 50) were correlated with miPSMA expression score and uptake. Physiologic tracer distribution was estimated by placing a volume of interest 1 cm in diameter for smaller organs (submandibular, parotid, lacrimal, and tubarial glands; renal cortices; blood pool; and bowel) and 3 cm for larger organs (liver and spleen). SUV_max and SUV_mean were estimated for each region. Tumor-to-spleen (T/S), tumor-to-liver (T/L), and tumor-to-parotid (T/P) ratios were calculated for each lesion. For 16 patients who underwent a delayed scan an average of 135 min after injection (120-150 min), additional analysis evaluated the effect of the delay. Results: Uptake was maximal in renal cortices, followed by salivary glands, bowel, spleen, liver, lacrimal glands, and blood pool. SUV_max averaged 37.7 ± 22.1 for renal cortices, 15.4 ± 7.3 for submandibular glands, 14.4 ± 7.1 for parotid glands, 9.4 ± 4.9 for spleen, 6.2 ± 3.7 for lacrimal glands, 5.9 ± 2.3 for liver, 5.3 ± 1.41 for tubarial glands, 13.8 ± 7.6 for bowel, and 2.4 ± 1.9 for blood pool. SUV_max averaged 10.33 ± 3.27 (6.46-17) for miPSMA expression score 2 and 38.21 ± 25.9 (7.68-119.08) for score 3. T/S and T/P ratios averaged 1.21 ± 0.44 (0.48-2.04) and 0.6 ± 0.18 (0.39-0.87), respectively, for score 2 and 5.05 ± 4.46 (1.25-20.89) and 3.15 ± 2.09 (1.06-9.45), respectively, for score 3. SUV_max for score 3 lesions averaged 18.85, which increased significantly to 26.24 on delayed imaging (P = 0.0001). However, T/L, T/S, and T/P ratios did not significantly change. Temporal variation in normal organs showed SUV_max to increase significantly on delayed scans for salivary (submandibular and parotid) and lacrimal glands and renal cortices, whereas SUV_mean increased significantly for spleen; liver; and parotid, tubarial, and lacrimal glands and insignificantly for other organs. Conclusion: These data form a basis for a proposed consensus on standard reference ranges for quantitative ⁶⁸Ga-PSMA-11 PET/CT. The temporal variations should be kept in mind for delayed acquisitions; T/S, T/L, and T/P ratios might serve as better markers for such scenarios.

Prostate Cancer Theranostics: From Target Description to Imaging

Prostate-specific membrane antigen-PET/computed tomography (PSMA-PET/CT) is the investigation of choice for imaging prostate cancer. Demonstrating high diagnostic accuracy, PSMA-PET/CT detects disease at very early stages of recurrence, where the chances of a definitive cure may be at their greatest. A number of PSMA-radioligands are in established clinical routine, and there are currently only limited data and no single tracer can clearly be advocated over the others at present. Further clinical trial data, comparing and contrasting radiotracers and reporting outcome-based data are necessary to further increase the implementation of this very promising imaging modality.

Novel Treatment Strategy Using Second-Generation Androgen Receptor Inhibitors for Non-Metastatic Castration-Resistant Prostate Cancer

Non-metastatic castration-resistant prostate cancer (nmCRPC) is defined by a progressively rising prostate-specific antigen level, despite a castrate level of testosterone, in the absence of obvious radiologic evidence of metastatic disease on conventional imaging modalities. As a significant proportion of patients with nmCRPC develop metastatic diseases, the therapeutic goals of physicians for these patients are to delay metastasis development, preserve quality of life, and increase overall survival (OS). Since 2018, the treatment of nmCRPC has changed dramatically with the introduction of second-generation androgen receptor inhibitors, such as enzalutamide (ENZA), apalutamide (APA), and darolutamide (DARO). These drugs demonstrated substantial improvements in metastasis-free survival (MFS) and OS in phase III randomized clinical trials. In addition, these drugs have an excellent safety profile, preserve quality of life, and can delay disease-related symptoms. A recently published indirect meta-analysis reported that APA and ENZA showed better findings in MFS and that DARO had relatively fewer adverse effects. However, in the absence of a direct comparison, careful interpretation is required. Thus, APA, ENZA, and DARO should be considered the new standard drugs for treating nmCRPC.

Impact of short-term Dutasteride treatment on prostate-specific membrane antigen expression in a mouse xenograft model

Background

Dutasteride has been shown to increase expression of the prostate‐specific membrane antigen (PSMA) in prostate cancer cells in previous in vitro studies. This 5‐alpha‐reductase inhibitor is commonly used for the treatment of symptomatic benign prostatic enlargement. The modulation of PSMA expression might affect PSMA‐based prostate cancer imaging and therapy.

Aim

The purpose of this work was to further analyze concentration‐dependent effects of Dutasteride on PSMA expression in a mouse xenograft model.

Methods and results

Four groups of mice bearing LNCaP xenografts were treated for 14 days with daily intraperitoneal injections of either vehicle control or different concentrations of Dutasteride (0.1, 1, 10 mg/kg). Total expression of PSMA, androgen receptor (AR), and caspase‐3 protein was analyzed using immunoblotting (WES). In addition, PSMA, cleaved caspase‐3 and Ki‐67 expression was assessed and quantified by immunohistochemistry. Tumor size was measured by caliper on day 7 and 14, tumor weight was assessed following tissue harvesting.

The mean PSMA protein expression in mice increased significantly after treatment with 1 mg/kg (10‐fold) or 10 mg/kg (sixfold) of Dutasteride compared to vehicle control. The mean fluorescence intensity significantly increased by daily injections of 0.1 mg/kg Dutasteride (1.6‐fold) as well as 1 and 10 mg/kg Dutasteride (twofold). While the reduction in tumor volume following treatment with high concentrations of 10 mg/kg Dutasteride was nonsignificant, no changes in AR, caspase‐3, cleaved caspase‐3, and Ki‐67 expression were observed.

Conclusion

Short‐term Dutasteride treatments with concentrations of 1 and 10 mg/kg significantly increase the total PSMA protein expression in a mouse LNCaP xenograft model. PSMA fluorescence intensity increases significantly even using lower daily concentrations of 0.1 mg/kg Dutasteride. Further investigations are needed to elucidate the impact of Dutasteride treatment on PSMA expression in patients.

Consensus statements on PSMA PET/CT response assessment criteria in prostate cancer

PURPOSE

Prostate-specific membrane antigen (PSMA) positron emission tomography (PET)/computed tomography (CT) is used for (re)staging prostate cancer (PCa) and as a biomarker for evaluating response to therapy, but lacks established response criteria. A panel of PCa experts in nuclear medicine, radiology, and/or urology met on February 21, 2020, in Amsterdam, The Netherlands, to formulate criteria for PSMA PET/CT-based response in patients treated for metastatic PCa and optimal timing to use it.

METHODS

Panelists received thematic topics and relevant literature prior to the meeting. Statements on how to interpret response and progression on therapy in PCa with PSMA PET/CT and when to use it were developed. Panelists voted anonymously on a nine-point scale, ranging from strongly disagree (1) to strongly agree (9). Median scores described agreement and consensus.

RESULTS

PSMA PET/CT consensus statements concerned utility, best timing for performing, criteria for evaluation of response, patients who could benefit, and handling of radiolabeled PSMA PET tracers. Consensus was reached on all statements. PSMA PET/CT can be used before and after any local and systemic treatment in patients with metastatic disease to evaluate response to treatment. Ideally, PSMA PET/CT imaging criteria should categorize patients as responders, patients with stable disease, partial response, and complete response, or as non-responders. Specific clinical scenarios such as oligometastatic or polymetastatic disease deserve special consideration.

CONCLUSIONS

Adoption of PSMA PET/CT should be supported by indication for appropriate use and precise criteria for interpretation. PSMA PET/CT criteria should categorize patients as responders or non-responders. Specific clinical scenarios deserve special consideration.

[18F]-JK-PSMA-7 and [18F]-FDG tumour PET uptake in treated xenograft human prostate cancer model in mice

PURPOSE

This preclinical study aims to evaluate the extent to which a change in prostate-specific membrane antigen (PSMA) expression of castration-resistant prostate cancer (CRPC) following standard treatment is reflected in [¹⁸F]JK-PSMA-7 PET/CT.

METHODS

Castrated mice supplemented with testosterone implant were xenografted with human LNCaP CRPC. After appropriate tumour growth, androgen deprivation therapy (ADT) was carried out by the removal of the implant followed by a single injection of docetaxel (400 μg/20-g mouse) 2 weeks later. [¹⁸F]JK-PSMA-7 PET/CT were performed before ADT, then before and at days 12, 26, 47 and 69 after docetaxel administration. The [¹⁸F]JK-PSMA-7 PET data were compared to corresponding unspecific metabolic [¹⁸F]FDG PET/CT and ex vivo quantification of PSMA expression estimated by flow cytometry on repeated tumour biopsies.

RESULTS

ADT alone had no early effect on LNCaP tumours that pursued their progression. Until day 12 post-docetaxel, the [¹⁸F]JK-PSMA7 uptake was significantly higher than that of [¹⁸F]FDG, indicating the persistence of PSMA expression at those time points. From day 26 onwards when the tumours were rapidly expanding, both [¹⁸F]JK-PSMA7 and [¹⁸F]FDG uptake continuously decreased although the decrease in [¹⁸F]JK-PSMA uptake was markedly faster. The fraction of PSMA-positive cells in tumour biopsies decreased similarly over time to reach a non-specific level after the same time period.

CONCLUSION

Applying PSMA-based imaging for therapy monitoring in patients with CRPC should be considered with caution since a reduction in [¹⁸F]JK-PSMA-7 PET uptake after successive ADT and chemotherapy may be related to downregulation of PSMA expression in dedifferentiated and rapidly proliferating tumour cells.

[18F]-JK-PSMA-7 PET/CT Under Androgen Deprivation Therapy in Advanced Prostate Cancer

PURPOSE

PSMA imaging is frequently used for monitoring of androgen deprivation therapy (ADT) in prostate cancer. In a previous study, [¹⁸F]-JK-PSMA-7 exhibited favorable properties for tumor localization after biochemical recurrence. In this retrospective study, we evaluated the performance of [¹⁸F]-JK-PSMA-7 under ADT.

PROCEDURES

We examined the performance of [¹⁸F]-JK-PSMA-7 in 70 patients (first cohort) with increasing or detectable PSA values under ADT (PSA < 2 ng/ml for 21/70 patients). We further analyzed 58 independent patients with PSA levels < 2 ng/ml under ADT, who were imaged with [⁶⁸Ga]PSMA-11 or [¹⁸F]DCFPyL (second cohort). Finally, we compared detection rates between [¹⁸F]-JK-PSMA-7, [⁶⁸Ga]PSMA-11, and [¹⁸F]DCFPyL.

RESULTS

In the first cohort, we detected [¹⁸F]-JK-PSMA-7-positive lesions in 63/70 patients. In patients with PSA levels ≥ 2 ng/ml, the detection rate was 100 % (49/49). In patients with PSA < 2 ng/ml, the detection rate was significantly lower (66.7 %, 14/21, p = 9.7 × 10^-5) and dropped from 85.7 % (12/14, PSA levels between 0.3 and 2.0 ng/ml) to 28.6 % (2/7) for PSA levels < 0.3 ng/ml (p = 1.73 × 10^-2). In the second cohort (PSA < 2 ng/ml), the detection rate was 79.3 % (46/58) for [⁶⁸Ga]PSMA-11 or [¹⁸F]DCFPyL. Again, the detection rate was significantly higher (p = 1.1 × 10^-2) for patients with PSA levels between 0.3 and 2.0 ng/ml (87.0 %, 40/46) relative to those with PSA levels < 0.3 ng/ml (50 %, 6/12). No significant difference was found between [¹⁸F]-JK-PSMA-7 and [⁶⁸Ga]PSMA-11 or [¹⁸F]DCFPyL in patients with PSA levels < 2 ng/ml (p = 0.4295).

CONCLUSION

[¹⁸F]-JK-PSMA-7 PET showed a high detection rate in patients with PSA levels ≥ 0.3 ng/ml under ADT. The lower PSA threshold of 0.3 ng/ml for high detection rates was consistent across the three PSMA ligands. Thus, PSMA imaging is suitable for clinical follow-up of patients with increasing PSA levels under ADT.