Prostate Brachytherapy Boost Does Not Prolong OS in Prostate Cancer at 15 Years

In prostate cancer, prostate brachytherapy (PB) boost improves biochemical failure at 10 years but does not prolong long-term overall survival (OS) compared to external beam radiotherapy (EBRT) boost, according to research presented at the ASCO Genitourinary Cancers Symposium 2026.

Previous studies have found that higher-dose radiotherapy improved biochemical control of localized prostate cancer, and the addition of androgen deprivation therapy improved survival, according to study presenter Scott Tyldesley, MD, of the University of British Columbia in Vancouver, Canada.

The phase 3 ASCENDE-RT trial (NCT00175396) included 398 patients with intermediate-risk or high-risk prostate cancer. The patients had a median age of 68 years at baseline and 82 years at follow-up. Most patients had high-risk disease (69.3%) and a Gleason score of 7 (53.8%).

The patients received androgen deprivation therapy for 1 year plus pelvic radiotherapy and were randomly assigned to receive 115 Gray PB boost implant (n=198) or conformal EBRT boost (n=200).

The ASCENDE-RT study met its primary endpoint, showing that PB prolonged 10-year freedom from biochemical failure compared to EBRT (85% vs 67%, respectively; P =.0004). The 15-year survival data were presented in this analysis.

During the 15-year follow-up, 54% of patients died, due to prostate cancer (16%), other cancers (12%), cardiovascular disease (9%), other known causes (12%), and unknown causes (4%). Of other known causes, the most common cause of death was dementia (n=21).

The 15-year OS rate was 60% among PB recipients and 55% among EBRT recipients, indicating no significant difference between the arms (hazard ratio [HR], 1.02; 95% CI, 0.78-1.33; P =.908).

However, the cumulative incidence of death from prostate cancer (CIDPCa) was lower among the PB recipients (8.6%) than the EBRT recipients (16.4%), indicating a significant prostate cancer-specific survival benefit with PB boost (HR, 0.52; 95% CI, 0.32-0.87; P =.012).

The significant CIDPCa outcome was attenuated when unknown death was coded as prostate cancer-related death (HR, 0.70; 95% CI, 0.46-1.08; P =.109).

This analysis was limited, as ASCENDE-RT was not specifically powered to detect OS or CIDPCa differences, Dr Tyldesley said.

 “Freedom from biochemical progression was 18% different to 10 years, which was the primary endpoint of ASCENDE,” Dr Tyldesley concluded. “There’s no difference in overall survival, at least not one that we can detect statistically, although we can’t really rule out a difference of 5% or even 10% with this data. There was a difference in death from prostate cancer, but it’s borderline significant.”

Disclosures: There was no funding for this study. Some study authors disclosed conflicts of interest. Please see the original reference for complete disclosures.