Extended Results and Independent Validation of a Phase 2 Trial of Metastasis Directed Therapy for Molecularly Defined Oligometastatic Prostate Cancer

Biochemical recurrence after radical prostatectomy and postoperative radiotherapy: current evidence and controversial issues

PURPOSE OF REVIEW

This review explores challenges in managing biochemical recurrence (BCR) after radical prostatectomy and postoperative radiotherapy for prostate cancer (PCa) highlighting gaps in risk stratification, imaging, and emerging therapies, as well as advances in molecular imaging and personalized treatment.

RECENT FINDINGS

Approximately half of PCa patients experience a second BCR after postoperative radiotherapy. Time to recurrence, PSA kinetics, adverse pathological features (ISUP 4-5, pT3-4, and positive surgical margins), alongside genetic profile, are key factors for risk stratification. Combination of androgen deprivation therapy (ADT) and novel androgen receptor pathway inhibitors (ARPIs) represents an established treatment choice. However, recent findings emphasize the growing role of prostate-specific membrane antigen (PSMA) PET in detecting recurrent disease and guide tailored strategies. Based on early phase II trials and retrospective studies, metastasis-directed therapy (MDT) has demonstrated promising efficacy in oligorecurrent PCa, although further validation is warranted.

SUMMARY

BCR after radical prostatectomy and postoperative radiotherapy represents a challenge in PCa management. Risk stratification is key for guiding the addition of ARPIs to standard ADT. PSMA PET may further refine tailored strategies such as MDT, whose promising efficacy needs further exploration. Ongoing trials will clarify treatment sequencing and patient selection in the evolving paradigm of BCR management.

Metastasis-Directed Therapy in Oligometastatic Prostate Cancer: Biological Rationale and Systematic Review of Published Data

INTRODUCTION

Metastasis-directed therapy (MDT) alone may be effective in preventing disease progression and positively affecting overall survival (OS) in oligometastatic prostate cancer (OMPC).

OBJECTIVE

We systematically reviewed the current literature to analyse the biological rationale for integrating MDT into treatment strategies for OMPC and investigate the current evidence on its role in OMPC.

EVIDENCE ACQUISITION

MEDLINE/PUBMED and the EMBASE Database were systematically searched to identify eligible reports published up to January 2024. The proceedings of the European Society for Radiotherapy and Oncology, European Society of Medical Oncology, American Society for Radiation Oncology, American Society of Clinical Oncology, European Uro-Oncology Group, and American Urological Association annual meetings were analysed.

RESULTS

Eighteen studies published between 2014 and 2024 were selected for the analysis. The studies included 1058 patients treated with metastasis-directed radiotherapy. No statistically significant differences were found in terms of treatment-escalation-free survival between hormone-naïve patients treated with MDT alone and those treated with MDT and hormonal manipulation. By contrast, the combination treatment significantly increased both 2 year and 4 year disease-progression-free survival (DPFS) rates (p-values < 0.00001 and 0.006, respectively). In patients with castration-sensitive disease treated with MDT alone, the estimated 2 year and 4 year OS rates were 96.4% (95% confidence interval [CI], 92.9-100%) and 89.1% (95% CI, 82.3-96.5%), respectively. The estimated 2 year and 4 year overall survival rates in the combination treatment group were 86.1% (95% CI 79.2-93.7%) and 74.8% (95% CI 64.6.3-86.5%), respectively.

CONCLUSIONS

MDT alone is associated with promising outcomes in OMPC and represents a valuable, valid, and often preferable strategy. Combined with ADT improves significantly disease-progression-free survival, but its impact on overall survival remains uncertain. Given these findings, the decision to incorporate ADT should be tailored to individual patient characteristics and clinical context. Future research should integrate biomarker-based approaches to optimise MDT use and select the best candidates for a multimodal approach.

Multi-institutional Analysis of Metastasis-directed Therapy with or Without Androgen Deprivation Therapy in Oligometastatic Castration-sensitive Prostate Cancer

BACKGROUND

Metastasis-directed therapy (MDT) is increasingly being used in oligometastatic castration-sensitive prostate cancer (omCSPC). However, it is currently unclear how to optimally integrate MDT with the standard of care of systemic hormonal therapy.

OBJECTIVE

To report long-term outcomes of MDT alone versus MDT and a defined course of androgen deprivation therapy (ADT) in omCSPC.

DESIGN, SETTING, AND PARTICIPANTS

Here, a multicenter, international retrospective cohort of omCSPC as defined by conventional imaging was reported.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

Biochemical progression-free survival (bPFS), distant progression-free survival (dPFS), and combined biochemical or distant progression-free survival (cPFS) were evaluated with Kaplan-Meier and multivariable Cox proportional hazard regression models.

RESULTS AND LIMITATIONS

A total of 263 patients were included, 105 with MDT + ADT and 158 with MDT alone. The majority of patients had metachronous disease (90.5%). Five-year bPFS, dPFS, and cPFS were, respectively, 24%, 41%, and 19% in patients treated with MDT + ADT and 11% (hazard ratio [HR] 0.48, 95% confidence interval [CI] 0.36-0.64), 29% (HR 0.56, 95% CI 0.40-0.78), and 9% (HR 0.50, 95% CI 0.38-0.67) in patients treated with MDT alone. On a multivariable analysis adjusting for pretreatment variables, the use of ADT was associated with improved bPFS (HR 0.43, p < 0.001), dPFS (HR 0.45, p = 0.002), and cPFS (HR 0.44, p < 0.001).

CONCLUSIONS

In this large multi-institutional report, the addition of concurrent ADT to MDT appears to improve time to prostate-specific antigen progression and distant recurrence, noting that about 10% patients had durable control with MDT alone. Ongoing phase 3 studies will help further define treatment options for omCSPC.

PATIENT SUMMARY

Here, we report a large retrospective review evaluating the outcomes of metastasis-directed therapy with or without a limited course of androgen deprivation for patients with oligometastatic castration-sensitive prostate cancer. This international multi-institutional review demonstrates that the addition of androgen deprivation therapy to metastasis-directed therapy (MDT) improves progression-free survival. While a proportion of patients appear to have long-term disease control with MDT alone, further work in biomarker discovery is required to better identify which patients would be appropriate for de-escalated therapy.

Recommendations on the treatment of metastatic hormone-sensitive prostate cancer: Patient selection

The standard treatment for metastatic hormone-sensitive prostate cancer (mHSPC) is now a combination of androgen deprivation therapy plus an androgen receptor-targeted therapy (abiraterone, apalutamide, enzalutamide or darolutamide), with or without chemotherapy (docetaxel). The selection of suitable patients for each therapeutic approach has become a determining factor to ensure efficacy and minimize side effects. This article combines recent clinical evidence with the accumulated experience of experts in medical oncology, radiation oncology and urology, to provide a comprehensive view and therapeutic recommendations for mHSPC.

Stereotactic ablative radiotherapy (SABR) for pelvic nodal oligorecurrence in prostate cancer

Background

This study evaluated the clinical outcomes of stereotactic ablative radiotherapy (SABR) in the treatment of oligometastatic pelvic node prostate cancer to delay androgen deprivation therapy (ADT).

Materials and methods

Pelvic lymph node metastases were identified by 11C-choline positron emission tomography (PET)-computed tomography (CT), and patients were not receiving ADT. SABR was administered using linear accelerators with intensity-modulated and image-guided radiotherapy, at a prescribed dose of 35 Gy in 5 fractions over 2 weeks. Response was assessed using Response Evaluation Criteria in Solid Tumours (RECIST) v1.1 criteria, and prostate-specific antigen (PSA) levels were monitored post-SABR. Toxicity and quality of life were assessed by the Common Terminology Criteria for Adverse Events Toxicity (CTCAE) v.5.0 and European Organisation for Research and Treatment of Cancer (EORTC) quality of life questionnaires QLQ-C30/QLQ-PR25, respectively. Kaplan-Meier and T-test were used for statistical analysis.

Results

Between June 2015 and November 2023, 56 patients with 85 lesions were treated at our institution. Median follow-up was 30 months [95% confidence interval (CI): 24-33.6]. Prostatectomy was the radical treatment in 85.7% of patients, and radiotherapy in 14.3%. Response rates were 67.1% for complete response, 27.4% for partial response, and 1.4% for stable disease. In-field progression was observed in only 3 lesions (3.5%). The median time to biochemical relapse post-SABR was 15 months (95% CI: 11.4-18.6). Three-year pelvic nodal and distant progression-free survival were 62.5% and 80%, respectively. There was a significant decrease in PSA levels after SABR compared to pretreatment levels (0.77 vs. 2.16 ng/mL respectively, p = 0.001). No grade ≥ 2 genitourinary or gastrointestinal toxicities. The median global health status score was 83.33 points at both time points analysed.

Conclusion

SABR can delay the ADT and provide excellent local control while preserving quality of life.

Metastasis-directed therapy in oligometastatic prostate cancer

PURPOSE OF REVIEW

To summarize the recent findings on the subject of metastasis-directed therapy (MDT) in the treatment of oligometastatic prostate cancer (omPCa).

RECENT FINDINGS

Evidence from two randomized clinical trials (RCTs) and a meta-analysis show favorable toxicity profiles, and the potential to delay androgen-deprivation therapy (ADT) for up to two years in nearly half of patients with metachronous hormone-sensitive omPCa. Another RCT showed promising results of MDT as treatment-escalation method combined with androgen receptor signaling inhibitors (ARSI) in first-line treatment for castration-resistant omPCa.Surveys by radiation oncologists and consensus guidelines advocate for MDT across various omPCa scenarios. Multiple single-arm trials present encouraging results; however, the evidence for the benefit of MDT is still weak requiring further investigation to assess its impact on pivotal endpoints, such as survival and quality of life.

SUMMARY

MDT is a promising approach in omPCa, and can be used to defer ADT in newly diagnosed metachronous omPCa patients, or to add to ARSI treatment at first diagnosis of castration-resistance. Ongoing prospective trials are needed to guide its optimal utilization in other settings, and patients should be informed about the evolving landscape of systemic therapies with proven survival benefits alongside MDT options.

[Metastasis-directed therapy in prostate cancer]

BACKGROUND

Metastasis-directed therapy (MDT) in oligometastatic prostate cancer (omHSPC) is playing an increasingly important role in therapy with the aim of delaying disease progression, the start of systemic treatment or switching systemic treatment to improve the patient's overall prognosis. Molecular imaging as prostate-specific membrane antigen positron emission tomography (PSMA-PET) imaging allows metastases to be detected with a higher sensitivity and specificity. This means that they can be detected early and made accessible for treatment.

RESULTS

The standard therapy for oligo-mHSPC is androgen deprivation (ADT), which is supplemented by novel hormonal therapeutics (NHT). A few small prospective trials have shown an extension of the ADT-free interval and progression-free survival (PFS), particularly in metachronous oligo-mHSPC, by MDT, usually radiotherapy. Additional ADT can further extend the PFS in particular. There are hardly any prospective data for synchronous oligo-mHSPC.

CONCLUSION

Despite the currently still poor evidence, MDT is playing an increasingly important role. The still unclear definition of oligometastasis and the large number of influencing factors make it difficult to compare current data. Large multicenter prospective data are still pending. It is also important to clarify the effect of limited ADT in combination with NHT in the treatment of synchronous and metachronous oligo-mHSPC with MDT. In synchronous oligo-mHSPC in particular, further benefit of additional local therapy of the primary in combination with MDT should also be investigated.

The Potential Contribution of Radiopharmaceutical Therapies in Managing Oligometastatic Disease

There is a growing understanding of the oligometastatic disease state, characterized by the presence of 5 or fewer lesions. Advanced molecular imaging techniques, such as prostate-specific membrane antigen PET, refines the ability to detect oligometastatic recurrences (oligorecurrences) early. These developments have led to the exploration of metastasis-directed therapy (MDT) in oligorecurrent disease as an alternative to or as a means of delaying systemic therapy. Unfortunately, MDT often does not provide a durable cure, and progression-particularly progression in multiple new areas-remains a concern. Simultaneously, developments in radioligand therapy (RLT) have led to studies showing overall survival benefits with α-emitting and β-emitting RLT in advanced, high-volume, metastatic castration-resistant prostate cancer. The success of RLT in late-stage disease suggests that earlier use in the disease spectrum may be impactful. Specifically, integration of RLT with MDT might reduce progression, including polymetastatic progression, in the setting of oligorecurrent disease.

The Efficacy and Safety of Metastasis-directed Therapy in Patients with Prostate Cancer: A Systematic Review and Meta-analysis of Prospective Studies

CONTEXT

Despite the lack of level 1 evidence, metastasis-directed therapy (MDT) is used widely in the management of metastatic prostate cancer (mPCa) patients. Data are continuously emerging from well-designed prospective studies.

OBJECTIVE

To summarise and report the evidence on oncological and safety outcomes of MDT in the management of mPCa patients.

EVIDENCE ACQUISITION

We searched the PubMed, Scopus, and Web of Science databases for prospective studies assessing progression-free survival (PFS), local control (LC), androgen deprivation therapy (ADT)-free survival (ADT-FS), overall survival (OS), and/or adverse events (AEs) in mPCa patients treated with MDT. A meta-analysis was performed for 1- and 2-yr PFS, LC, ADT-FS, OS, and rate of AEs. Meta-regression and sensitivity analysis were performed to account for heterogeneity and identify moderators.

EVIDENCE SYNTHESIS

We identified 22 prospective studies (n = 1137), including two randomised controlled trials (n = 116). Two studies were excluded from the meta-analysis (n = 120). The estimated 2-yr PFS was 46% (95% confidence interval [CI]: 36-56%) or 42% (95% CI: 33-52%) after excluding studies using biochemical or ADT-related endpoints. The estimated 2-yr LC, ADT-FS, and OS were 97% (95% CI: 94-98%), 55% (95% CI: 44-65%), and 97% (95% CI: 95-98%), respectively. Rates of treatment-related grade 2 and ≥3 AEs were 2.4% (95% CI: 0.2-7%) and 0.3% (95% CI: 0-1%), respectively.

CONCLUSIONS

MDT is a promising treatment strategy associated with favourable PFS, excellent LC, and a low toxicity profile that allows oligorecurrent hormone-sensitive patients to avoid or defer ADT-related toxicity. Integration of MDT with other therapies offers a promising research direction, in particular, in conjunction with systemic treatments and as a component of definitive care for oligometastatic PCa. However, in the absence of randomised trials, using MDT for treatment intensification remains an experimental approach, and the impact on OS is uncertain.

PATIENT SUMMARY

Direct treatment of metastases is a promising option for selected prostate cancer patients. It can delay hormone therapy and is being investigated as a way of intensifying treatment at the expense of manageable toxicity.

Association of PSMA PET-derived Parameters and Outcomes of Patients Treated for Oligorecurrent Prostate Cancer

Background Prostate-specific membrane antigen (PSMA) PET is useful in the early detection of oligorecurrent prostate cancer (PCa), but whether PSMA PET parameters can be used to identify patients who would benefit from metastasis-directed therapy (MDT) with radiation or surgery remains uncertain. Purpose To assess the association of PSMA PET parameters with outcomes of patients with oligorecurrent PCa after MDT. Materials and Methods In this retrospective analysis of a single-center phase II trial that enrolled patients with biochemical recurrence of PCa after maximal local therapy and with no evidence of disease at conventional imaging, patients underwent PSMA PET (between May 2017 and November 2021), and unveiled recurrences were treated with MDT. Maximum standardized uptake value (SUVmax) and mean standardized uptake value (SUVmean) and PSMA tumor volume derived using thresholds of 2.5 (SUVmean2.5) and 41% (SUVmean41%), respectively, were recorded for sites of recurrence on PSMA PET scans, and a molecular imaging PSMA score was assigned. These parameters were also corrected for smooth filter and partial volume effects, and the PSMA score was reassigned. Cox proportional hazards models were used to evaluate the relationship between PSMA PET parameters and outcomes. Results A total of 74 men (mean age, 68.3 years ± 6.6 [SD]) with biochemical recurrence of PCa were included. PSMA PET revealed 145 lesions in the entire cohort, of which 125 (86%) were metastatic lymph nodes. Application of the correction factor changed the PSMA score in 88 of 145 lesions (61%). Mean SUVmax, SUVmean2.5, and SUVmean41% were associated with lower risk of biochemical progression (hazard ratio [HR] range, 0.77-0.95; 95% CI: 0.61, 1.00; P = .03 to P = .04). For corrected parameters, mean SUVmax, mean SUVmean2.5, mean SUVmean41%, mean PSMA score, maximum SUVmean2.5, maximum SUVmean41%, and maximum PSMA score were associated with a lower risk of biochemical progression (HR, 0.61-0.98; 95% CI: 0.39, 1.00; P = .01 to P = .04). Conclusion Measured and corrected PSMA PET parameters were associated with biochemical progression in men with oligorecurrent PCa treated with MDT. Clinical trial registration no. NCT03160794 © RSNA, 2023 See also the editorial by Civelek in this issue.

The diagnosis and treatment of castrate-sensitive oligometastatic prostate cancer: A review

BACKGROUND

Oligometastatic prostate cancer (OMPCa) is emerging as a transitional disease state between localized and polymetastatic disease. This review will assess the current knowledge of castrate-sensitive OMPCa.

METHODS

A review of the current literature was performed to summarize the definition and classification of OMPCa, assess the diagnostic methods and imaging modalities utilized, and to review the treatment options and outcomes. We further identify gaps in knowledge and areas for future research.

RESULTS

Currently there is no unified definition of OMPCa. National guidelines mostly recommend systemic therapies without distinguishing oligometastatic and polymetastatic disease. Next generation imaging is more sensitive than conventional imaging and has led to early detection of metastases at initial diagnosis or recurrence. While mostly retrospective in nature, recent studies suggest that treatment (surgical or radiation) of the primary tumor and/or metastatic sites might delay initiation of androgen deprivation therapy while increasing survival in selected patients.

CONCLUSIONS

Prospective data are required to better assess the incremental improvement in survival and quality of life achieved with various treatment strategies in patients with OMPCa.

Node Oligorecurrence in Prostate Cancer: A Challenge

Within the oligometastatic state, oligorecurrent lymph node disease in prostate cancer represents an interesting clinical entity characterized by a relatively indolent biology that makes it unique: it can be treated radically, and its treatment is usually associated with a long period of control and excellent survival. Additionally, it is an emergent situation that we are facing more frequently mainly due to (a) the incorporation into clinical practice of the PSMA-PET that provides strikingly increased superior images in comparison to conventional imaging, with higher sensitivity and specificity; (b) the higher detection rates of bone and node disease with extremely low levels of PSA; and (c) the availability of high-precision technology in radiotherapy treatments with the incorporation of stereotaxic body radiotherapy (SBRT) or stereotaxic ablative radiotherapy (SABR) technology that allows the safe administration of high doses of radiation in a very limited number of fractions with low toxicity and excellent tolerance. This approach of new image-guided patient management is compelling for doctors and patients since it can potentially contribute to improving the clinical outcome. In this work, we discuss the available evidence, areas of debate, and potential future directions concerning the utilization of new imaging-guided SBRT for the treatment of nodal recurrence in prostate cancer.

Oligometastasis in Prostate Cancer: Can We Learn from Those "Excluded" from a Phase 2 Trial?

We conducted and previously published a phase 2 trial of metastasis-directed therapy (MDT) in men with recurrence of prostate cancer at a low prostate-specific antigen level following radical prostatectomy and postoperative radiotherapy. All patients had negative conventional imaging and underwent prostate-specific membrane antigen (PSMA) positron emission tomography (PET). Patients without visible disease (n = 16) or with metastatic disease not amenable to MDT (n = 19) were excluded from the interventional study. The remaining patients with disease visible on PSMA-PET received MDT (n = 37). We analyzed all three groups to identify distinct phenotypes in the era of molecular imaging-based characterization of recurrent disease. Median follow up was 37 mo (interquartile range 27.5-43.0). There was no significant difference in time to the development of metastasis on conventional imaging among the groups; however, castrate-resistant prostate cancer-free survival was significantly shorter for patients with PSMA-avid disease not amenable to MDT (p = 0.047). Our findings suggest that PSMA-PET findings can help in discriminating diverging clinical phenotypes among men with disease recurrence and negative conventional imaging after local therapies with curative intent. There is a pressing need for better characterization of this rapidly growing population of patients with recurrent disease defined by PSMA-PET to derive robust selection criteria and outcome definitions for ongoing and future studies.

Patient summary

In men with prostate cancer with rising PSA levels following surgery and radiation, a newer type of scan called PSMA-PET (prostate-specific membrane antigen positron emission tomography) can be used to characterize and differentiate the patterns of recurrence, and inform future cancer outcomes.