Reviews/Targeted Therapy Prostate Cancer/Enzalutamide overall survival benefit in metastatic castration-resistant prostate cancer
Arpi · PC-ARPI-01 · v2
The claim is about a specific trial, PREVAIL, which tested enzalutamide against placebo in men with advanced prostate cancer who had not yet had chemotherapy. The trial first reported a clear survival advantage at an early look and then confirmed a lasting survival advantage after more than five years of follow-up, with men on the drug living a median of 36 months versus 31 months on placebo [1][4]. This benefit held up even though many men originally on placebo later received other effective drugs, which would tend to make the two groups look more alike [1]. A separate trial in Asian patients in the same setting also found survival improved on the drug, and a trial in men who had already had chemotherapy found a similar survival benefit [2][3]. The panel relied mainly on the named trial itself, with the other trials pointing in the same direction, and noted the survival gain comes alongside somewhat higher rates of fatal side effects [1].
The named PREVAIL trial randomised 1717 chemotherapy-naive men and reported a 29% reduction in risk of death at interim (hazard ratio 0.71; 95% CI 0.60-0.84; P<0.001) [4]. Its final prespecified 5-year analysis confirmed a durable benefit (hazard ratio 0.83; 95% CI 0.75-0.93; p<0.001), with median overall survival of 36 months versus 31 months, despite 65%, 54%, and 43% of placebo patients receiving subsequent docetaxel, abiraterone, and enzalutamide [1]. An independent chemotherapy-naive RCT in Asian patients reports 5-year overall survival significantly improved as a secondary endpoint, though it quotes no overall-survival hazard ratio [2]. The post-chemotherapy AFFIRM RCT shows a survival benefit in an adjacent population (median 18.4 vs 13.6 months; hazard ratio 0.63; 95% CI 0.53-0.75; P<0.001) [3]. The contested point: The precise chemotherapy-naive survival-versus-placebo estimate rests principally on PREVAIL itself, since the one independent chemo-naive RCT [2] reports overall survival only as a secondary endpoint with no hazard ratio and the strongest corroborating estimate [3] comes from a different, post-chemotherapy population. The interim hazard ratio of 0.71 [4] also attenuated to 0.83 in the mature analysis [1], so the headline early figure overstates the effect that the less-biased final estimate supports.
All 14 papers behind this claim with their DOIs and what each does to it, the panel’s arbitration, the evidence gap map and the open research questions. Free, and sent to your inbox.
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One reviewer's only job is to attack the finding. The challenges below were weighed before the grade was set.
The interim HR of 0.71 [4] attenuated to 0.83 in the mature final analysis [1]; the claim should rest on the less-biased mature estimate, which remains significant but is a weaker effect than the headline interim figure.
Large fractions of placebo patients crossed to subsequent effective therapies (65% docetaxel, 54% abiraterone, 43% enzalutamide) [1], biasing the OS contrast toward the null — the benefit is conservative, but the comparison against a truly untreated control is unobservable.
Where it remains uncertain. The effect attenuated from an interim hazard ratio of 0.71 [4] to 0.83 [1], and the chemo-naive-specific estimate leans on PREVAIL alone, since [2] quotes no overall-survival hazard ratio and [3] is a post-chemotherapy population.
Aleatory
Prognostic modeling in PREVAIL showed 5-year survival rates of 42%, 24%, and 5% across low-, intermediate-, and high-risk groups [1], so the median benefit masks wide individual variation in outcome.
Epistemic
[2] reports 5-year overall survival as significantly improved but quotes no overall-survival hazard ratio, so a second precise chemo-naive estimate is not available in the corpus.
Inferential
With 65%, 54%, and 43% of placebo patients receiving subsequent docetaxel, abiraterone, and enzalutamide [1], the comparison is against an actively re-treated control, not an untreated one, so the observed benefit is a conservative lower bound.
The load-bearing papers from a corpus of 14, each classified by what it does to the claim. Every DOI is taken from the corpus the claim was graded on.
Final mature OS of PREVAIL confirms a durably significant survival benefit even against heavy placebo-arm crossover.
“Median overall survival was 36 mo (95% CI 34-38) in the enzalutamide arm versus 31 mo (95% CI 29-34) in the placebo arm, with a median follow-up of 69 mo.”
Panel auditInternal validity: high · scope of inference: Men with chemotherapy-naive metastatic castration-resistant prostate cancer; long-term overall survival.Key limitations: substantial crossover to subsequent effective therapies in placebo arm · higher fatal cardiovascular events with enzalutamide
Independent chemo-naive mCRPC RCT corroborates a significant OS improvement with enzalutamide over placebo.
“Secondary endpoints, including 5-year overall survival, were significantly improved with enzalutamide, except time to first SRE.”
Panel auditInternal validity: medium · scope of inference: Asian men with chemotherapy-naive mCRPC progressing despite ADT.Key limitations: separate trial, not PREVAIL · no OS hazard ratio or CI given in abstract · study stopped at interim analysis
Post-chemotherapy mCRPC RCT provides supporting, adjacent-population evidence of an enzalutamide OS benefit vs placebo.
“The median overall survival was 18.4 months (95% confidence interval [CI], 17.3 to not yet reached) in the enzalutamide group versus 13.6 months (95% CI, 11.3 to 15.8) in the placebo group (hazard ratio for death in the enzalutamide group, 0.63; 95% CI, 0.53 to 0.75; P<0.001).”
Panel auditInternal validity: high · scope of inference: Men with metastatic castration-resistant prostate cancer after chemotherapy; overall survival.Key limitations: post-chemotherapy population, not chemotherapy-naive · different trial (AFFIRM) than the one claimed
3 of 14 papers shown. The full review lists all of them, with the panel’s arbitration →
Claims are graded at each quarterly release, and re-graded between releases only when a pivotal trial lands. Every change is a new version of the claim.
The claim is carried directly by its named trial with a statistically significant, mature, hard-outcome OS result, corroborated by independent RCTs, with only minor discounts for HR attenuation and crossover bias.
Release 2026-q4 re-graded every claim from its corpus under protocol v0.19. An earlier release's grade is shown for the record; it came from an earlier protocol and is not a movement.
Assumptions that carry weight but are not themselves established.
The panel records the gap that would most move the claim, and the study that would close it.
Independent chemo-naive OS hazard ratio. The exact chemo-naive survival effect rests on a single named trial; the one independent same-population RCT [2] reports no overall-survival hazard ratio. The panel rates this the highest-importance open gap for the claim, and names the study design that would close it: A chemotherapy-naive mCRPC RCT reporting overall survival as a primary endpoint with a hazard ratio and confidence interval against placebo.
Open question: What is the overall-survival hazard ratio for enzalutamide versus placebo in chemotherapy-naive mCRPC outside PREVAIL? Why it is still open: The only independent same-population RCT in the corpus [2] reports 5-year overall survival as significantly improved but quotes no hazard ratio.
Priors is a sceptical first reader, not peer review, and not medical advice.
Release 2026-q4 · graded 26 Oct 2026 · protocol v0.19