Pattern of Clinical Progression Until Metastatic Castration-Resistant Prostate Cancer: An Epidemiological Study from the European Prostate Cancer Registry

The role of radium-223 in the evolving treatment landscape of metastatic castration-resistant prostate cancer: A narrative review

The treatment of metastatic castration-resistant prostate cancer (mCRPC) has been rapidly evolving over the last two decades. The advent of new androgen receptor pathway inhibitors (ARPIs) such as abiraterone acetate or enzalutamide marks a great advance for treating mCRPC patientd in the pre- and post-docetaxel settings. The subsequent approval of ARPIs in early stages-i.e., metastatic hormone-sensitive (mHSPC) or nonmetastatic CRPC-led to a realignment of subsequent treatment choices upon progression to mCRPC, given the possibility of cross-resistance between ARPIs. Therapies with mechanisms of action different from those of ARPIs are now the focus of new treatment developments. Also, this anomalous situation brings the focus back to well-known treatments currently used later in the treatment sequence. This is the case of radium-223 which, when administered with enzalutamide, has recently been shown to prolong radiographic progression-free survival vs. enzalutamide alone in the first line in asymptomatic or mildly symptomatic patients with no known visceral metastases. In this narrative review, we summarize the treatment landscape for mCRPC, both from a historical and practical point of view, to understand the new potential of radium-223 as a treatment option in this setting.

Pembrolizumab Plus Docetaxel Versus Docetaxel for Previously Treated Metastatic Castration-Resistant Prostate Cancer: The Randomized, Double-Blind, Phase III KEYNOTE-921 Trial

PURPOSE

The standard of care for metastatic castration-resistant prostate cancer (mCRPC) after second-generation androgen receptor pathway inhibitor (ARPI) therapy is still docetaxel. The randomized, double-blind, phase III KEYNOTE-921 trial (Clinicaltrials.gov identifier: NCT03834506) evaluated the efficacy and safety of pembrolizumab or placebo plus docetaxel for previously treated mCRPC.

METHODS

Adults with mCRPC who progressed after androgen-deprivation therapy and one ARPI were randomly assigned 1:1 to pembrolizumab or placebo plus docetaxel with concomitant prednisone. Dual primary end points were radiographic progression-free survival (rPFS) by blinded independent central review per Prostate Cancer Working Group 3-modified RECIST 1.1 and overall survival (OS). Safety was a secondary end point.

RESULTS

Between May 30, 2019, and June 17, 2021, 515 participants were randomly assigned to pembrolizumab plus docetaxel and 515 to placebo plus docetaxel. Median time from random assignment to data cutoff date (June 20, 2022) at final analysis (FA) was 22.7 months (range, 12.1-36.7). At first interim analysis (data cutoff date: September 27, 2021), median rPFS was 8.6 months (95% CI, 8.3 to 10.2) with pembrolizumab plus docetaxel versus 8.3 months (95% CI, 8.2 to 8.5) with placebo plus docetaxel (hazard ratio [HR], 0.85 [95% CI, 0.71 to 1.01]; P = .03). At FA, median OS was 19.6 months (95% CI, 18.2 to 20.9) versus 19.0 months (95% CI, 17.9 to 20.9), respectively (HR, 0.92 [95% CI, 0.78 to 1.09]; P = .17). Grade ≥3 treatment-related adverse events occurred in 43.2% of participants who received pembrolizumab plus docetaxel and 36.6% of participants who received placebo plus docetaxel. Two and seven participants, respectively, died due to a treatment-related adverse event. Pneumonitis was the most common immune-mediated adverse event (7.0% v 3.1%).

CONCLUSION

The addition of pembrolizumab to docetaxel did not significantly improve efficacy outcomes for participants with previously treated mCRPC. The current standard of care remains unchanged.

[225Ac]Ac-PSMA for the treatment of metastatic castration-resistant prostate cancer: A systematic review and meta-analysis

BACKGROUND

Approximately 10%-20% of prostate cancers progress to metastatic and castration-resistant forms (mCRPC). Radioligand (RLT) therapy with [177Lu]Lu-prostate-specific membrane antigen (PSMA) is an approved treatment for metastasized mCRPC. Moreover, Actinium-225 (225Ac), an alpha-emitter isotope, has also been used to label PSMA and, recently, to treat mCRPC patients with encouraging results. However, robust clinical data on [225Ac]Ac-PSMA therapy and its comparison with [177Lu]Lu-PSMA are still limited. Our aim was to evaluate the role of [225Ac]Ac-PSMA in treating mCRPC and compare it with conventional [177Lu]Lu-PSMA therapy.

METHODS

A systematic search was performed in PubMed, Web of Science, Scopus and the Cochrane Register of Controlled Trials from June 2023 to January 2024. This work was conducted in accordance with PRISMA guidelines.

RESULTS

After screening and study selection according to PRISMA guidelines, 11 studies were included, 9 of which focused on [225Ac]Ac-PSMA only and two on tandem therapy ([225Ac]Ac-PSMA/[177Lu]Lu-PSMA). Overall, the pooled proportion of PSA decline in patients was .85 (95% CI: .79-.91, p < .001); patients pretreated with [177Lu]Lu-PSMA achieved a pooled proportion of PSA decline of .90 (95% CI: .82-.97, p < .001). In patients treated with tandem therapy, PSA decline was observed in approximately 90% of them, while PSA response rates above 50% ranged from 53.3% to 65%. Xerostomia was the most frequently reported side effect, along with anaemia, thrombocytopenia and nephrotoxicity.

CONCLUSIONS

Overall, the main results of our study showed that [225Ac]Ac-PSMA-617 had a significant therapeutic effect on mCRPC with an acceptable toxicity level. The latter, however, appears greater than with [177Lu]Lu-PSMA-617. In future studies, an adequate analysis of the incidence of side effects associated with [225Ac]Ac-PSMA should be performed to evaluate the role of cumulative toxicity of earlier treatments and the higher frailty of heavily pretreated patients.

Real-world treatment patterns and genetic testing in a metastatic castration-resistant prostate cancer setting in Europe

AIM

This study described treatment patterns, reasons for treatment, and homologous recombination repair mutation (HRRm) testing patterns in a real-world metastatic castration-resistant prostate cancer (mCRPC) population in Europe.

METHODS

Data were drawn from the Adelphi Prostate Cancer Disease Specific Programme™, a cross-sectional survey of physicians and patients conducted in France, Germany, Italy, Spain, and the United Kingdom, November 2022-May 2023. Physicians provided clinical characteristics, treatment and HRRm testing patterns, and reasons for treatment for eight consecutive patients with mCRPC. Most analyses were descriptive; treatment reasons were compared using Fisher's Exact test.

RESULTS

Physicians provided data for 1,737 mCRPC patients. Most patients (73%) were androgen receptor pathway inhibitor (ARPi)-naïve at first-line (1 L) mCRPC. Here, at 1 L mCRPC, 60% of patients received ARPi and 24% chemotherapy. Of those who received ARPi prior to mCRPC (n = 291), 60% received chemotherapy at mCRPC and 21% ARPi. Overall, 37% were HRRm tested. Treatment patterns, sequencing, reasons, and HRRm testing varied by country, physician specialty, and practice setting.

CONCLUSIONS

Treatment patterns generally followed guidelines. ARPi prescriptions prior to mCRPC were numerically higher than previously reported, however HRRm testing rates were still low meaning mCRPC patients may miss out on more effective targeted treatments.

Treatment intensification with radium-223 plus enzalutamide in patients with metastatic castration-resistant prostate cancer

Several life-prolonging therapies with diverse mechanisms of action (MoA) are available for the treatment of metastatic hormone-sensitive/castration-resistant prostate cancer, with many patients requiring multiple lines of therapy. Nevertheless, treatment optimization to further delay disease progression and improve overall survival remains an unmet need. Despite the number of agents with differing MoAs approved for advanced prostate cancer, many patients receive only one or two life-prolonging therapies. One strategy for enhancing the benefit of treatment for this aggressive disease is combining therapies with different MoAs (treatment intensification) early in the disease course, which may be more effective than administering therapies sequentially, yet still allow for subsequent sequential use of individual therapies to optimize patient outcomes. In this narrative review we discuss the rationale for combining 223radium dichloride (223Ra; an alpha-emitting radionuclide) with enzalutamide (an androgen receptor inhibitor) for treatment intensification, including their differing MoAs, their individual efficacy in this setting, and their largely non-overlapping tolerability profiles. We also summarize the preclinical and clinical data available for this combination to date, including interim safety data from the phase 3 EORTC 1333/PEACE III study which highlight the low fracture risk of 223Ra plus enzalutamide when administered concomitantly with bone health agents. Relevant data were sourced from clinical studies published by the authors and via searches of PubMed, clinical trial registries and congress abstracts.

Identifying Suitable Patients for Overcoming Androgen Deprivation Monotherapy in De Novo Metastatic Hormone-Sensitive Prostate Cancer

BACKGROUND

Although metastatic hormone-sensitive prostate cancer (mHSPC) treatments have evolved, androgen deprivation therapy (ADT) remains a widely used regimen. Therefore, this study sought patients who did not progress to castration-resistant prostate cancer (CRPC) but received ADT monotherapy and factors affecting overall survival (OS) in de novo mHSPC.

METHODS

De novo mHSPC patients who received ADT treatment were included. ADT included luteinizing hormone-releasing hormone agonists with or without anti-androgen. The total cohort was divided into two groups relative to CRPC progression within two years. Logistic analysis was used to identify factors that did not progress CRPC within two years. Cox regression was used to assess the independent predictors for OS.

RESULTS

The total cohort was divided into the no-CRPC within two years group (n = 135) and the CRPC within two years group (n = 126). Through multivariate logistic analysis, the life expectancy (odds ratio [OR] 0.95, 95% CI 0.91-0.99, p = 0.014) and Gleason scores (≥9 vs. ≤8; OR 0.43, 95% CI 0.24-0.75, p = 0.003) were associated with the group without castration-resistant prostate cancer progression within two years. The multivariate Cox model revealed that life expectancy (hazard ratio [HR] 0.951, 95% CI 0.904-0.999, p = 0.0491), BMI (HR 0.870, 95% CI 0.783-0.967, p = 0.0101), and CCI (≥2 vs. <2; HR 2.018, 95% CI 1.103-3.693, p = 0.0227) were significant predictive factors for OS.

CONCLUSIONS

Patients with long life expectancy and a Gleason score of 9 or more were more likely to develop mCRPC while alive. Patients with short life expectancy, low BMI, and worsening comorbidity were more likely to die before progressing to CRPC. Although intensified treatment is essential for oncologic outcomes in mHSPC, shared decision making is integral for patients who may not benefit from this treatment.

First-line combination treatment with PARP and androgen receptor-signaling inhibitors in HRR-deficient mCRPC: Applying clinical study findings to clinical practice in the United States

INTRODUCTION

Metastatic castration-resistant prostate cancer (mCRPC) remains incurable and develops from biochemically recurrent PC treated with androgen deprivation therapy (ADT) following definitive therapy for localized PC, or from metastatic castration-sensitive PC (mCSPC). In the mCSPC setting, treatment intensification of ADT plus androgen receptor (AR)-signaling inhibitors (ARSIs), with or without chemotherapy, improves outcomes vs ADT alone. Despite multiple phase 3 trials demonstrating a survival benefit of treatment intensification in PC, there remains high use of ADT monotherapy in real-world clinical practice. Prior studies indicate that co-inhibition of AR and poly(ADP-ribose) polymerase (PARP) may result in enhanced benefit in treating tumors regardless of alterations in DNA damage response genes involved either directly or indirectly in homologous recombination repair (HRR). Three recent phase 3 studies evaluated the combination of a PARP inhibitor (PARPi) with an ARSI as first-line treatment for mCRPC: TALAPRO-2, talazoparib plus enzalutamide; PROpel, olaparib plus abiraterone acetate and prednisone (AAP); and MAGNITUDE, niraparib plus AAP. Results from these studies have led to the recent approval in the United States of talazoparib plus enzalutamide for the treatment of mCRPC with any HRR alteration, and of both olaparib and niraparib indicated in combination with AAP for the treatment of mCRPC with BRCA alterations.

SUMMARY

Here, we review the newly approved PARPi plus ARSI treatments within the context of the mCRPC treatment landscape, provide an overview of practical considerations for the combinations in clinical practice, highlight the importance of HRR testing, and discuss the benefits of treatment intensification for patients with mCRPC.

Synthetic Lethality by Co-Inhibition of Androgen Receptor and Polyadenosine Diphosphate-Ribose in Metastatic Prostate Cancer

Androgen receptor pathway inhibitors (ARPI) and polyadenosine diphosphate-ribose inhibitors (PARPi) are part of the standard of care in patients with metastatic castration-resistant prostate cancer (mCRPC). There is biological evidence that the association of ARPI and PARPi could have a synergistic effect; therefore, several ongoing clinical trials are investigating the efficacy of this combination with preliminary results that are not perfectly concordant in identifying patients who can obtain the most benefit from this therapeutic option. The purpose of this review is to describe the PARPi mechanisms of action and to analyze the biological mechanisms behind the interplay between the androgen receptor and the PARPi system to better understand the rationale of the ARPI + PARPi combinations. Furthermore, we will summarize the preliminary results of the ongoing studies on these combinations, trying to understand in which patients to apply. Finally, we will discuss the clinical implications of this combination and its possible future perspectives.

Intermittent Radioligand Therapy with 177Lu-PSMA-617 for Oligometastatic Castration-Resistant Prostate Cancer

177Lu-PSMA-617 radioligand therapy (177Lu-PSMA-RLT) in patients with metastatic castration-resistant prostate cancer (mCRPC) currently consists of 4-6 cycles of 6.0-7.4 GBq of 177Lu-PSMA-617 each every 6-8 weeks. While safety and efficacy could be demonstrated in larger prospective trials irrespective of the tumor burden at 177Lu-PSMA RLT initiation, increased renal absorbed doses due to a reduced tumor sink effect in early responding, oligometastatic mCRPC patients pose difficulties. Response-adapted, dose distributing, intermittent treatment with up to six cycles has not been routinely performed, due to concerns about the potential loss of disease control. Treatment was discontinued in 19 early-responding patients with oligometastatic tumor burden after two (IQR 2-3) cycles of 177Lu-PSMA-RLT and 6.5 ± 0.7 GBq per cycle and resumed upon 68Ga-PSMA-11-PET/CT-based progression (according to the PCWG3 criteria). Subsequent treatment breaks were imposed if a PSMA-based imaging response could be achieved. A total of five (IQR 3-6) cycles reaching a cumulative activity of 32 ± 11 GBq were applied. A routine blood work-up including blood counts and liver and renal function was measured throughout the 177Lu-PSMA-RLT and follow-up to grade toxicity according to CTCAE v5.0 criteria. Survival outcome was calculated based on the Kaplan-Meier method. In total, treatment-free periods of 9 (IQR 6-17) cumulative months and the application of 177Lu-PSMA-RLT cycles over 16 (IQR 9-22) months could be achieved. Fifteen (84%) patients responded to subsequent cycles after the first treatment break and in 7/19 (37%) patients, intermittent 177Lu-PSMA-RLT consisted of ≥2 treatment breaks. The median PFS was 27 months (95% CI: 23-31) and overall survival was 45 months (95% CI: 28-62). No grade ≥3 hematological or renal toxicities could be observed during the 45 ± 21 months of follow-up. The cumulative mean renal absorbed dose was 16.7 ± 8.3 Gy and 0.53 ± 0.21 Gy/GBq. Intermittent radioligand therapy with 177Lu-PSMA-617 is feasible in early-responding patients with oligometastatic disease. A late onset of progression after subsequent cycles and the absence of significant toxicity warrants further investigation of the concept of intermittent treatment in selected patients.

Prognostic role of early prostate specific antigen changes after [177 Lu]Lu-PSMA radioligand therapy of metastasized prostate cancer: A meta-analysis

BACKGROUND

Approximately 10%-20% of prostate cancers progress to metastatic and castration-resistant forms (mCRPC). Radioligand (RLT) therapy with [177 Lu]Lu-prostate-specific membrane antigen (PSMA) is an emerging treatment for metastasized mCRPC and its efficacy is assessed not only but also by prostate specific antigen (PSA) measurement after 12 weeks or more after treatment. Our aim was to evaluate the role of early PSA measurement after RLT in predicting overall survival (OS) of mCRPC patients.

METHODS

A systematic search on PubMed, Web Of Science and Scopus was performed from January to December 2022. PRISMA guidelines for prognostic studies was adopted. Risk of bias was assessed using quality of prognostic studies (QUIPS).

RESULTS

Twelve studies at low-intermediate risk of bias, were included in the meta-analysis (1646 patients, mean age 70 years). About 50% of patients showed a PSA decline after 1-2 of [177 Lu]Lu-PSMA, and more than 30% reported a PSA decline ≥50%. The median OS range for patients with any PSA decline was 13-20 months, while for patients with stable or increased PSA, the median OS fell to 6-12 months. The OS rate for a PSA decline after the one-two [177 Lu]Lu-PSMA cycles was 0.39 (95% CI: 0.31-0.50), while OS for a PSA decline ≥50% was 0.69 (95% CI: 0.57-0.83).

CONCLUSIONS

A PSA decline is observed in almost 50% of mCRPC patients after 1-2 [177 Lu]Lu-PSMA cycles, with a significantly longer OS compared to stable or increased PSA levels, respectively. Accordingly, any PSA decline after 1-2 cycles of therapy should be regarded as a favourable prognostic factor for OS.