Review of Prospective Trials Assessing the Role of Stereotactic Body Radiation Therapy for Metastasis-directed Treatment in Oligometastatic Genitourinary Cancers

Oligometastatic Urothelial Cancer and Stereotactic Body Radiotherapy: A Systematic Review and an Updated Insight of Current Evidence and Future Directions

BACKGROUND

Stereotactic body radiation therapy (SBRT) is the most commonly used metastasis-directed therapy (MDT) for oligometastatic urothelial carcinoma (omUC). Despite efforts in defining this disease entity, open questions remain concerning the role of MDT and the use of biomarkers, imaging, and its combination with systemic therapies. The aim of the present systematic review is to provide an updated overview of the current clinical evidence on SBRT for omUC in terms of survival and local control benefits. We also aim to provide updates on controversial areas and future directions in this emerging field.

METHODS

With a systematic approach, following PRISMA recommendations, we searched two databases to identify and select articles published up until March 2024 reporting the use of SBRT for omUC with or without concomitant systemic therapies. Prospective randomized or non-randomized studies as well as retrospective studies were included.

RESULTS

Eight studies were selected for data extraction and 293 omUC patients treated with SBRT were collectively analyzed. In metachronous omUC patients, SBRT delivered with ablative doses (BED10 ≥ 78 Gy) was associated with a 2-year overall survival (OS) rate of 50.7% (95% CI 35.1-64.4%). The use of sub-ablative SBRT doses (BED10 = 43.2 Gy) in combination with immunotherapy did not demonstrate significant clinical outcome improvement in two prospective studies. The overall tolerance was good, with only one study reporting toxicity of grade 3 in up to 18% of the patients treated with SBRT in combination with immunotherapy.

CONCLUSIONS

SBRT is an effective and widely available MDT option in omUC, although this is based on a limited number of studies. Despite the attempt to use SBRT as an immune response trigger in combination with immunotherapy, no significant improvement in survival outcomes has been observed. The integration of new systemic agents with MDT will likely define a new scenario for the treatment of omUC. The review protocol was registered in PROSPERO, ID: CRD42024522381.

Is there a role for metastasis-directed therapy in bladder cancer?

PURPOSE OF REVIEW

This article aims to comprehensively review and critique the existing literature on the role of metastatic-directed therapy in patients with metastatic bladder cancer, particularly in oligometastatic disease state.

RECENT FINDINGS

The role of metastasectomy in metastatic bladder cancer is still controversial. Several studies have demonstrated improved outcomes, particularly in a highly selected patients with small metastatic lesions or with lung or brain metastases, whereas others show no significant survival benefit. Combining metastasectomy with systemic therapies, such as immunotherapy and chemotherapy, has also shown benefits. Metastasis-directed radiotherapy is evolving as a potentially effective approach with minimal toxicity in achieving local control and improving survival, particularly in patients with oligometastatic disease. The evidence regarding the impact of several factors such as performance status, metastatic burden, and the presence of visceral metastases on outcomes is mixed. Concurrent treatment with systemic therapy may potentiate the effectiveness of metastasis-directed therapy.

SUMMARY

In patients with metastatic deposits amenable to surgical resection, metastasectomy stands as a promising avenue. Metastatic-directed radiotherapy has demonstrated local control and improved survival in the evolving landscape of oligometastatic bladder cancer management. Further, well designed multicenter prospective studies are needed to support these findings and better understand the synergy between radiotherapy and systemic treatments, especially immunotherapy.

Systemic and Tumor-directed Therapy for Oligorecurrent Metastatic Prostate Cancer (SATURN): Primary Endpoint Results from a Phase 2 Clinical Trial

Nearly all men with metastatic hormone-sensitive prostate cancer treated with intermittent androgen deprivation therapy (ADT) experience recurrence within 6 mo of testosterone recovery. We conducted a single-arm phase 2 trial to evaluate whether addition of dual androgen receptor pathway inhibitors (ARPIs) and metastasis-directed stereotactic body radiotherapy (SBRT) to intermittent ADT improves recurrence rates for men with between one and five nonvisceral, extrapelvic metastases on prostate-specific membrane antigen positron emission tomography/computed tomography after prior radical prostatectomy. Patients received 6 mo of androgen annihilation therapy (AAT; leuprolide, abiraterone acetate plus prednisone, and apalutamide) and metastasis-directed SBRT. The primary endpoint was the percentage of patients with prostate-specific antigen (PSA) <0.05 ng/ml 6 mo after testosterone recovery (≥150 ng/dl), with the study powered to detect an improvement from 1% to 12%. We enrolled 28 men between March 2021 and June 2022. Median follow-up was 20 mo (interquartile range 16-22). Twenty-six patients (93%) completed SBRT with 6 mo of hormone therapy, of whom six discontinued at least one ARPI; two patients withdrew prematurely. At 6 mo after testosterone recovery, PSA was maintained at <0.05 ng/ml in 13/26 patients (50%, 95% confidence interval 32-67%). Rates of grade 2 and 3 AAT toxicity were 21% and 21%. The results confirm that addition of metastasis-directed SBRT to highly potent systemic therapy can maintain low PSA after testosterone recovery, although further studies are needed to clarify the optimal systemic therapy regimen. PATIENT SUMMARY: We tested a combination of intensified hormone therapy (called androgen annihilation therapy) and radiotherapy targeted at metastases in men with recurrence of metastatic prostate cancer. We found that half of patients were recurrence-free 6 months after their testosterone level recovered, and that less than a quarter of patients experienced a severe drug-related side effect. Overall, this appears to be an effective therapy with acceptable side effects. This trial is registered on ClinicalTrials.gov as NCT03902951.

Role of Metastasis-Directed Therapy in Genitourinary Cancers

OPINION STATEMENT

The treatment of oligometastatic genitourinary cancers is a rapidly advancing field with ablative radiotherapy as one of the critical treatment components. The oligometastatic disease state, which can be defined as 1-5 metastatic sites with a controlled primary, represents a distinct clinical state where comprehensive ablative local therapies may provide improved outcomes. Enhanced imaging has increased the number of patients identified with oligometastatic disease. Evidence for improved outcomes with metastasis-directed therapy (MDT) in oligometastatic genitourinary cancers is increasing, and previously published outcome data continues to mature with an increasing body of prospective data to inform the role of MDT in histology-specific settings or in the context of systemic therapy. In select patients, MDT can offer benefits beyond improved local control and allow for time off of systemic therapy, prolonged time until next therapy, or even the hope of cure. However, treatment decisions for locally ablative therapy must be balanced with consideration towards safety. There are exciting advances in technologies to target and adapt treatment in real-time which have expanded options for safer delivery and dose escalation to metastatic targets near critical organs at risk. The role of systemic therapies in conjunction with MDT and incorporation of tumor genetic information to further refine prognostication and treatment decision-making in the oligometastatic setting is actively being investigated. These developments highlight the evolving field of treatment of oligometastatic disease. Future prospective studies combining MDT with enhanced imaging and integrating MDT with evolving systemic therapies will enable the optimal selection of patients most likely to benefit from this "all-or-none" approach and reveal settings in which a combination of therapies could result in synergistic outcomes.

Definitions, outcomes and perspectives for oligometastatic bladder cancer: towards a standardized terminology

PURPOSE OF REVIEW

Oligometastatic (om) cancer is considered as a transitional state in between locally confined disease and widespread metastases, accessible to a multimodal treatment, combining systemic and local therapy. In urothelial bladder cancer (BCa), the definitions and the approaches to this condition are poorly standardised and mainly based on retrospective data. We aim to portray the framework for uro-oncologic terminology in omBCa and go through the latest evidence and the future perspectives.

RECENT FINDINGS

Retrospective and registry data support the potential benefits of multimodality treatment for carefully selected omBCa patients, especially following a good response to systemic treatment. In 2023, a Delphi consensus has defined omBCa, allowing maximum three metastatic lesions, theoretically amenable to radical local treatment. In de-novo omBCa, surgical treatment of primary tumour might improve overall survival (OS), according to a matched registry analysis; also, consolidative radiotherapy was associated with better OS in two recent cohorts. Furthermore, metastasis-directed therapy (MDT) has shown high local control rates and promising OS (14.9-51 months) in a meta-analysis; benefits might be more pronounced for single-site omBCa and nodal or lung lesions.

SUMMARY

From a clinical perspective, in de-novo omBCa, the local treatment of primary and metastatic sites might improve disease control and survival, in selected patients; in the oligorecurrent setting, MDT achieves good local symptom control with limited side effects; in selected cases, it could convey a survival benefit, too. From a research perspective, well designed prospective evidence is eagerly awaited, based on recently adopted shared definitions for omBCa.

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.

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.