SUMMARY: Prostate cancer is the most common cancer in American men with the exclusion of skin cancer, and 1 in 9 men will be diagnosed with Prostate cancer during their lifetime. It is estimated that in the United States, about 333,830 new cases of Prostate cancer will be diagnosed in 2026 and 36,320 men will die of the disease. Androgen Deprivation Therapy (ADT) or testosterone suppression has been the cornerstone of treatment of advanced Prostate cancer, and is the first treatment intervention.
The major source of PSA (Prostate Specific Antigen) is the prostate gland, and the PSA levels are therefore undetectable within 6 weeks after Radical Prostatectomy. Similarly, following radiation therapy there is a gradual decline in PSA, before reaching a post treatment nadir. A detectable PSA level after Radical Prostatectomy, or a rising PSA level following radiation therapy, is considered PSA failure or biochemical recurrence. Approximately 35% of the patients with prostate cancer will experience PSA only relapse within 10 years of their primary treatment, and a third of these patients will develop documented metastatic disease within 8 years following PSA only relapse. Rising PSA is therefore a sign of recurrent disease. Patients with biochemically relapsed prostate cancer following local therapy, and a short PSA doubling time, are at risk for distant metastases.
Enzalutamide (XTANDI®) is a potent oral Androgen Receptor Pathway Inhibitor with demonstrated efficacy in patients with both localized and advanced prostate cancer.
EMBARK is a randomized, double-blind, placebo-controlled, multi-national, Phase III trial, conducted to evaluate the efficacy and safety of Enzalutamide plus Leuprolide and Enzalutamide monotherapy, as compared with Leuprolide alone, in patients with non-metastatic Hormone/Castration-Sensitive Prostate Cancer (nmHSPC or nmCSPC) prostate cancer, who have had high-risk biochemical recurrence. In this study, a total of 1068 eligible patients were randomly assigned 1:1:1 to receive Enzalutamide at 160 mg orally once daily plus Leuprolide IM every 12 weeks (N=355), single agent Enzalutamide at 160 mg orally once daily (N=355) or Leuprolide alone (N=358). All patients had received prior definitive therapy with radical prostatectomy and/or radiotherapy with curative intent. High risk disease was defined as a PSA doubling time of 9 months or less and a PSA level of 2 ng/ml above nadir after radiation therapy, or 1 ng/ml or more after radical prostatectomy with or without postoperative radiation therapy. The baseline characteristics were well balanced among the treatment groups. The median age was 69 years, the median PSA doubling time was 4.9 months and the median PSA level was 5.2 ng/ml. The Primary end point was Metastasis-Free Survival (MFS), as assessed by Blinded Independent Central Review (BICR) in the combination group, as compared with the Leuprolide-alone group. MFS is defined as the duration of time in months between randomization and the earliest objective evidence of radiographic progression by central imaging or death due to any cause, whichever occurred first. Secondary end points included MFS in the Enzalutamide monotherapy group, as compared with the Leuprolide-alone group, Overall Survival (OS), Patient-Reported Outcomes and Safety.
At a median follow up 60.7 months, the 5 year MFS was 87.3% in the Enzalutamide combination group and 71.4% with Leuprolide alone (HR for metastasis or death 0.42; P<0.001). This represented a 58% lower risk of metastasis or death in the combination group than Leuprolide alone among patients with biochemically recurrent prostate cancer. At the time of this analysis, Overall Survival data were immature.
In this publication, the final Overall Survival (OS) analysis of the Phase 3 EMBARK trial provided compelling long-term evidence supporting intensified Androgen-Receptor Pathway Inhibition in patients with high-risk biochemical recurrence of prostate cancer and no evidence of metastasis on conventional imaging. At the time of this final analysis, 277 deaths had occurred: 73 in the combination arm, 111 in the Leuprolide-alone arm, and 93 in the Enzalutamide monotherapy arm. Median follow-up exceeded 93 months across all treatment groups, offering a robust long-term perspective on survival outcomes.
Overall Survival: Durable and Clinically Meaningful Benefit
The combination of Enzalutamide plus Leuprolide demonstrated a statistically and clinically significant improvement in OS compared with Leuprolide alone:
- 8-year OS:
- 78.9% (95% CI, 73.9–83.1) with combination therapy
- 69.5% (95% CI, 64.0–74.3) with Leuprolide alone
- Hazard ratio for death: 0.60 (95% CI, 0.44–0.80; P<0.001)
This 40% relative reduction in mortality risk translates into an absolute improvement of nearly 10% at 8 years, a notable achievement in a population historically managed with Androgen Deprivation Therapy (ADT) alone.
By contrast, Enzalutamide monotherapy did not significantly improve OS relative to Leuprolide alone:
- 8-year OS: 73.1% (95% CI, 67.6–77.9)
- Hazard ratio: 0.83 (95% CI, 0.63–1.10; P=0.19)
While monotherapy previously demonstrated improvements in key Secondary endpoints, including Metastasis-Free Survival, it did not confer a statistically significant survival advantage in this final OS analysis.
Descriptive updates of Secondary endpoints were consistent with earlier reports. Time to first use of new antineoplastic therapy and time to first symptomatic skeletal event continued to favor combination therapy.
Although fractures were numerically more frequent in the combination arm, this reflected a broader category of bone and joint injuries. Importantly, the time to first symptomatic skeletal event was prolonged with Enzalutamide plus Leuprolide compared with Leuprolide alone, suggesting lower clinically meaningful skeletal morbidity despite the higher overall reporting of fractures.
Safety Profile: No New Signals
The long-term safety data remained consistent with earlier analyses. No new safety signals emerged, and the adverse-event profile of Enzalutamide, whether used in combination or as monotherapy, aligned with prior experience in metastatic castration-resistant and metastatic castration-sensitive prostate cancer settings.
Clinical Context: Imaging Evolution and Treatment Implications
Interpretation of these results must consider the evolving imaging landscape. At the time of trial enrollment, staging relied on CT or MRI for soft-tissue assessment and radionuclide bone scans for osseous disease. With the increasing use of PSMA PET imaging, it is likely that a proportion of patients categorized as nonmetastatic in the trial may have harbored occult locoregional or oligometastatic disease detectable by more sensitive modalities. Nevertheless, the study reflects real-world practice standards at the time and provides a pragmatic framework for treatment decision-making in high-risk biochemical recurrence.
Treatment Suspension Strategy: A Unique Feature
An important protocol component was treatment suspension at week 37 for patients achieving undetectable PSA (<0.2 ng/mL), with reinitiation upon PSA rise to predefined thresholds. This strategy aimed to mitigate toxicity and preserve quality of life. Notably, the OS benefit of combination therapy was achieved despite these mandated treatment interruptions.
Future research should clarify:
- Which patients may safely undergo treatment suspension,
- Whether continuous therapy could further optimize outcomes in select populations,
- And how molecular imaging findings should inform early intensification strategies.
Positioning in the Treatment Paradigm
The final OS data reinforce earlier MFS findings and establish Enzalutamide plus ADT as a preferred standard of care for patients with Castration-Sensitive Prostate Cancer and high-risk biochemical recurrence without conventional radiographic metastases.
Although Enzalutamide monotherapy remains a reasonable option, particularly for patients prioritizing preservation of sexual function based on patient-reported outcomes, shared decision-making remains essential, balancing efficacy, toxicity, and quality-of-life considerations.
Conclusion
With nearly eight years of follow-up, the EMBARK trial confirms that intensification of Androgen-Receptor Pathway Inhibition with Enzalutamide plus Leuprolide delivers a durable Overall Survival advantage in high-risk biochemical recurrence. These findings extend the survival benefits observed with Enzalutamide across earlier disease states and further reshape management strategies in this evolving therapeutic space.
Improved Survival with Enzalutamide in Biochemically Recurrent Prostate Cancer. Shore ND, Luz MA, Giorgi UD, et al. N Engl J Med 2026;394:563-575.
