Why this matters
Six months of androgen deprivation therapy improves disease control when added to radiotherapy for intermediate-risk prostate cancer, but the sexual and quality-of-life consequences can be substantial.
Darolutamide offers an attractive biological alternative because it blocks androgen receptor signaling without suppressing circulating testosterone to the same extent as conventional ADT.
INTREPID asked a clinically important question: can darolutamide replace short-course ADT during prostate radiotherapy and preserve sexual function without compromising oncologic activity?
The first answer is mixed. Erectile function was substantially better with darolutamide, but the trial failed its prespecified noninferiority endpoint for early PSA suppression.
Study design
INTREPID was a randomized phase II trial enrolling men with intermediate-risk prostate cancer and good baseline erectile function.
Patients were randomized 1:1 to:
- 6 months of conventional ADT with a GnRH agonist plus bicalutamide and radiotherapy
- 6 months of darolutamide monotherapy and radiotherapy
Radiotherapy began approximately 8-12 weeks after initiation of systemic therapy.
Patients were stratified by:
- number of unfavorable intermediate-risk factors
- radiotherapy modality
- age younger than 65 vs 65 or older
A range of radiation approaches was permitted, including IMRT, SBRT, and brachytherapy-containing regimens.
A total of 234 patients were randomized:
- 121 to ADT
- 113 to darolutamide
The primary endpoint tested whether darolutamide was noninferior to conventional ADT for achieving an early PSA nadir of 0.5 ng/mL or lower between the end of treatment and 6 months afterward.
The prespecified noninferiority margin was 9 percentage points.
A hierarchical endpoint evaluated preservation of good erectile function at 3 months after treatment, but this endpoint was formally testable only if the primary noninferiority endpoint was met.
Key results
The primary endpoint was negative.
A PSA nadir of 0.5 ng/mL or lower was achieved in:
- 99.1% with conventional ADT
- 90.8% with darolutamide
The absolute difference was:
- 8.3 percentage points
However, the upper bound of the two-sided 95% confidence interval was:
- 14.4%
Because this exceeded the prespecified 9% noninferiority margin, darolutamide did not establish noninferiority for early PSA suppression.
Erectile function
Sexual function strongly favored darolutamide.
Good erectile function at 3 months after treatment was maintained in:
- 43.6% with conventional ADT
- 71.9% with darolutamide
The EPIC-26 sexual domain also showed substantially better preservation of sexual function with darolutamide throughout treatment and early follow-up.
However, because the primary noninferiority endpoint was not met, the erectile function endpoint cannot be interpreted as a formally positive hierarchical endpoint.
It is therefore best considered an exploratory but clinically compelling signal.
Toxicity and hormonal effects
The adverse-event profile reflected the different biological effects of the two systemic strategies.
Conventional ADT produced substantially more hot flashes, while darolutamide was associated with more breast-related symptoms, including breast pain and gynecomastia.
The sexual-function findings were consistent with the expected preservation of testosterone signaling outside the androgen receptor blockade produced by darolutamide.
This is precisely what makes the strategy attractive, but the oncologic tradeoff remains unresolved.
Interpretation
INTREPID illustrates the fundamental challenge of replacing conventional ADT with a testosterone-preserving androgen receptor inhibitor.
The quality-of-life signal is clear.
Approximately 72% of men receiving darolutamide maintained good erectile function at 3 months after treatment compared with 44% receiving conventional ADT.
But preserving sexual function was not the trial's only requirement.
To replace ADT, darolutamide also had to demonstrate sufficiently similar oncologic activity. On the prespecified early PSA endpoint, it failed to do so.
That does not mean darolutamide has been shown to produce worse long-term cancer control.
The trial measured early PSA suppression, not biochemical recurrence, metastasis-free survival, or overall survival. A smaller proportion of patients reaching a very low PSA nadir cannot automatically be translated into inferior long-term oncologic outcomes.
But the opposite inference is equally inappropriate. The favorable erectile-function results cannot justify replacing conventional ADT while the oncologic consequences remain uncertain.
The trial therefore lands in an important intermediate position.
Darolutamide demonstrates that androgen receptor blockade without conventional testosterone suppression can preserve substantially more sexual function during prostate radiotherapy. But the strategy has not yet shown that it can preserve the oncologic efficacy expected from ADT.
The planned 3-year PSA control analysis will be much more informative for that question.
Limitations
The current analysis focuses on early PSA suppression rather than long-term oncologic outcomes.
The erectile-function endpoint became exploratory because the prespecified hierarchical testing procedure stopped after failure of the primary noninferiority endpoint.
Radiotherapy treatment was heterogeneous, with IMRT, SBRT, and brachytherapy-containing approaches permitted.
Patient-reported sexual outcomes were also affected by questionnaire attrition.
Finally, the study population was deliberately selected for good baseline erectile function, so the magnitude of sexual-function preservation may not generalize to all men receiving radiotherapy for intermediate-risk prostate cancer.