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

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.

Prognostic Performance of RECIP 1.0 Based on [18F]PSMA-1007 PET in Prostate Cancer Patients Treated with [177Lu]Lu-PSMA I&T

In metastatic castration-resistant prostate cancer (mCRPC) patients treated with prostate-specific membrane antigen (PSMA)-targeted radioligand therapy (RLT), the recently proposed criteria for evaluating response to PSMA PET (RECIP 1.0) based on 68Ga- and 18F-labeled PET agents provided prognostic information in addition to changes in prostate-specific antigen (PSA) levels. Our aim was to evaluate the prognostic performance of this framework for overall survival (OS) in patients undergoing RLT and imaged with [18F]PSMA-1007 PET/CT and compare the prognostic performance with the PSA-based response assessment. Methods: In total, 73 patients with mCRPC who were scanned with [18F]PSMA-1007 PET/CT before and after 2 cycles of RLT were retrospectively analyzed. We calculated the changes in serum PSA levels (ΔPSA) and quantitative PET parameters for the whole-body tumor burden (SUVmean, SUVmax, PSMA tumor volume, and total lesion PSMA). Men were also classified following the Prostate Cancer Working Group 3 (PCWG3) criteria for ΔPSA and RECIP 1.0 for PET imaging response. We performed univariable Cox regression analysis, followed by multivariable and Kaplan-Meier analyses. Results: Median OS was 15 mo with a median follow-up time of 14 mo. Univariable Cox regression analysis provided significant associations with OS for ΔPSA (per percentage, hazard ratio [HR], 1.004; 95% CI, 1.002-1.007; P < 0.001) and PSMA tumor volume (per unit, HR, 1.003; 95% CI, 1.000-1.005; P = 0.03). Multivariable Cox regression analysis confirmed ΔPSA (per percentage, HR, 1.004; 95% CI, 1.001-1.006; P = 0.006) as an independent prognosticator for OS. Kaplan-Meier analyses provided significant segregation between individuals with versus those without any PSA response (19 mo vs. 14 mo; HR, 2.00; 95% CI, 0.95-4.18; P = 0.04). Differentiation between patients with or without progressive disease (PD) was also feasible when applying PSA-based PCWG3 (19 mo vs. 9 mo for non-PD and PD, respectively; HR, 2.29; 95% CI, 1.03-5.09; P = 0.01) but slightly failed when applying RECIP 1.0 (P = 0.08). A combination of both response systems (PCWG3 and RECIP 1.0), however, yielded the best discrimination between individuals without versus those with PD (19 mo vs. 8 mo; HR, 2.78; 95% CI, 1.32-5.86; P = 0.002). Conclusion: In patients with mCRPC treated with RLT and imaged with [18F]PSMA-1007, frameworks integrating both the biochemical (PCWG3) and PET-based response (RECIP 1.0) may best assist in identifying subjects prone to disease progression.

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

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

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.

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.

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

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

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSION

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

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

BACKGROUND

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

OBJECTIVE

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

DESIGN, SETTING, AND PARTICIPANTS

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

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

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

RESULTS AND LIMITATIONS

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

CONCLUSIONS

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

PATIENT SUMMARY

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

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

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

The Impact of PSMA PET/CT on Modern Prostate Cancer Management and Decision Making-The Urological Perspective

Prostate-specific membrane antigen (PSMA) PET use in prostate cancer treatment has recently become a routinely used imaging modality by urologists. New, established data regarding its performance in different stages of prostate cancer, as well as gaining clinical knowledge with new tracers, drives the need for urologists and other clinicians to improve the utilization of this tool. While the use of PSMA PET/CT is more common in metastatic disease, in which it outperforms classical imaging modalities and drives treatment decisions and adjustments, recently, it gained ground in localized prostate cancer as well, especially in high-risk disease. Still, PSMA PET/CT might reveal lesions within the prostate or possibly locoregional or metastatic disease, not always representing true cancer when utilized in earlier stages of the disease, potentially adding diagnostic burden and changing treatment decisions. As urological treatment options advance toward focal treatments in localized organ-confined prostate cancer, recent reports suggest the utilization of PSMA PET/CT in treatment planning and follow-up and even when choosing active surveillance. This review aims to reveal the current perspective of urologists regarding its daily use.

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.

Clinical advancement of precision theranostics in prostate cancer

Theranostic approaches with positron emission tomography/computed tomography (PET/CT) or PET/magnetic resonance imaging (PET/MRI) molecular imaging probes are being implemented clinically in prostate cancer (PCa) diagnosis and imaging-guided precision surgery. This review article provides a comprehensive summary of the rapidly expanding list of molecular imaging probes in this field, including their applications in early diagnosis of primary prostate lesions; detection of lymph node, skeletal and visceral metastases in biochemical relapsed patients; and intraoperative guidance for tumor margin detection and nerve preservation. Although each imaging probe shows preferred efficacy in some applications and limitations in others, the exploration and research efforts in this field will eventually lead to improved precision theranostics of PCa.