This page separates reported trial results from statistical interpretation. Numerical results are taken from the publicly reported ClinicalTrials.gov record. The registry provides the official trial record.
1. Trial at a Glance
ARASENS was a randomized, parallel-group, quadruple-masked phase 3 trial evaluating darolutamide in addition to standard androgen deprivation therapy and docetaxel in patients with metastatic hormone-sensitive prostate cancer. The registry reports two primary time-to-event outcome measures for overall survival and eight formal statistical analyses, including one primary-endpoint analysis.
| Feature | ARASENS |
|---|---|
| Phase | Phase 3 |
| Condition | Metastatic hormone-sensitive prostate cancer |
| Design | Randomized, parallel-group |
| Masking | Quadruple |
| Primary purpose | Treatment |
| Enrollment | 1306 |
| Primary endpoint type | Time-to-event |
| Primary endpoints registered | 2 |
| Formal statistical analyses posted | 8 |
| Results posted | Yes |
| Lead sponsor | Bayer |
| ClinicalTrials.gov | NCT02799602 |
2. Clinical Question
The statistical question is whether adding darolutamide to standard androgen deprivation therapy and docetaxel changes time-to-event outcomes compared with placebo plus docetaxel in metastatic hormone-sensitive prostate cancer.
Population
Participants with metastatic hormone-sensitive prostate cancer enrolled in the ARASENS phase 3 trial.
Intervention
BAY1841788 / darolutamide (ODM-201), together with standard androgen deprivation therapy and docetaxel.
Comparator
Placebo plus docetaxel, with standard androgen deprivation therapy forming part of the trial treatment framework.
Primary question
Does the darolutamide-containing treatment strategy produce a statistically superior overall-survival time-to-event outcome compared with the placebo-containing strategy?
3. Trial Design
Darolutamide + Docetaxel
- BAY1841788 / darolutamide (ODM-201)
- Standard androgen deprivation therapy
- Docetaxel
Placebo + Docetaxel
- Placebo
- Standard androgen deprivation therapy
- Docetaxel
The treatment comparison is therefore not a simple comparison of darolutamide versus no therapy. The registered groups compare a darolutamide-containing treatment strategy with a placebo-containing strategy within a randomized trial framework that includes standard androgen deprivation therapy and docetaxel.
4. Primary Endpoints
| Registered endpoint | Time frame | Endpoint type | Formal analysis |
|---|---|---|---|
| OS From Date of Randomization Until Death From Any Cause - Number of Events | From randomization of the first participant until death from any cause up to 25 OCT 2021 cut-off date; 533 OS events were reached (approximate 59 months) | Time-to-event | Stratified one-sided log-rank test; HR from stratified Cox regression |
| OS From Date of Randomization Until Death From Any Cause - Month | From randomization of the first participant until death from any cause up to 25 OCT 2021 cut-off date; 533 OS events were reached (approximate 59 months) | Time-to-event | Primary endpoint measure posted; the formal statistical analysis is reported for the OS event endpoint |
Registry definition of overall survival
Overall survival was defined as the time from the date of randomization until death from any cause. The registered treatment period states that treatment was provided twice daily until disease progression, symptomatic progressive disease, change of systemic antineoplastic therapy, unacceptable toxicity, consent withdrawal, withdrawal at the discretion of the investigator, death, or non-compliance. Active follow-up visits from the discontinuation of the darolutamide or placebo treatment period for up to 1 year or until the patient could no longer travel to the clinic, died, was lost to follow-up, or withdrew informed consent and actively objected to collection of further data. Long-term (Survival) follow-up period: After Active follow-up, patients continued to be contacted approximately every 12 weeks by phone. The end of the Survival follow-up period was defined as when the patient died, was lost to follow-up, withdrew consent, or at the end-of-study.
The primary endpoint therefore has a clear time origin—randomization—and a clearly defined event—death from any cause. This structure is important statistically because participants who have not experienced death by the analysis cutoff are not simply treated as if they had survived indefinitely; their follow-up is handled through time-to-event methods and censoring.
5. Statistical Methodology
Primary comparison: stratified log-rank test
The registry reports a log-rank test as the formal method for the primary overall-survival comparison. The analysis notes specify a one-sided p-value and stratification by extent of disease (EOD) and alkaline phosphatase (ALP).
The formal hypothesis type was superiority. The registry therefore describes a directional test in which the analysis evaluates whether the darolutamide-containing arm has a lower hazard than the placebo-containing arm.
Cox regression for the hazard ratio
The reported hazard ratio and its 95% confidence interval were based on a Cox regression model stratified by EOD and ALP. The EOD categories were specified as non-regional lymph-node metastases only; bone metastases with or without lymph-node metastases; and visceral metastases with or without lymph-node metastases or with or without bone metastases. ALP was categorized as <ULN versus ≥ULN.
The registry explicitly states that an HR below 1 indicates superiority of the darolutamide + docetaxel arm over the placebo + docetaxel arm.
Why both methods are reported
The log-rank test and Cox model answer related but distinct statistical questions. The log-rank test supplies the formal comparison of the time-to-event distributions, while the Cox model provides a relative effect estimate—the hazard ratio—and its confidence interval.
This distinction matters because a p-value alone does not communicate the magnitude or precision of an effect. Conversely, a hazard ratio without its uncertainty interval does not show how precisely the treatment effect has been estimated.
6. Primary Overall Survival Result
The primary analysis compared darolutamide (BAY1841788) + docetaxel with placebo + docetaxel. The registry reports 533 OS events at the 25 OCT 2021 cutoff.
Hazard ratio for overall survival
95% CI: 0.568–0.801 · One-sided P < 0.0001
Method: stratified log-rank test; HR and 95% CI from stratified Cox regression
| Primary endpoint | Darolutamide + Docetaxel vs Placebo + Docetaxel |
|---|---|
| OS events | 533 |
| Hazard ratio | 0.675 |
| 95% confidence interval | 0.568–0.801 |
| P-value | <0.0001 |
| Hypothesis | Superiority |
| Test | One-sided stratified log-rank |
| Cox model | Stratified by EOD and ALP |
An HR of 0.675 means that, under the fitted Cox model, the estimated instantaneous hazard of death in the darolutamide + docetaxel group was 0.675 times that in the placebo + docetaxel group. Expressed as a relative complement, this corresponds to an estimated 32.5% lower hazard because 1 − 0.675 = 0.325.
The HR does not mean that 32.5% of participants avoided death, that 32.5% of participants benefited, or that every participant experienced the same reduction in individual risk. It is a relative time-to-event measure derived from the Cox model.
The 95% CI of 0.568–0.801 describes statistical uncertainty around the estimated hazard ratio under the analysis framework. It does not describe the range of treatment effects across individual patients.
The p-value <0.0001 addresses the evidence against the null hypothesis under the specified one-sided log-rank testing framework. It does not measure the size of the treatment effect. The effect size is described by the HR, while its precision is described by the confidence interval.
Because the effect estimate comes from a Cox model, interpretation also depends on the appropriateness of the proportional-hazards framework. The registry does not provide enough information in the ClinicalTrials.gov record to evaluate the proportional-hazards assumption directly.
What the primary result establishes statistically
The posted analysis is explicitly a superiority analysis. The HR is below 1, the 95% confidence interval is 0.568–0.801, and the one-sided log-rank p-value is <0.0001. Taken together, these are the reported statistical components of the primary comparison.
The appropriate interpretation is narrower than saying that darolutamide "reduces mortality by 32.5%" in an absolute sense. The result is a model-based relative hazard comparison between the randomized treatment strategies over the analysis period.
7. Secondary Time-to-Event Results
The registry contains seven additional formal statistical analyses. Each uses the same broad framework: a log-rank test, one-sided testing, stratification by EOD and ALP, and a hazard ratio based on a Cox regression model stratified by those factors.
| Secondary endpoint | HR | 95% CI | P-value |
|---|---|---|---|
| Time to Castration-Resistant Prostate Cancer | 0.357 | 0.302–0.421 | <0.0001 |
| Time to Pain Progression | 0.792 | 0.660–0.950 | 0.0058 |
| Symptomatic Skeletal Event Free Survival (SSE-FS) | 0.609 | 0.516–0.718 | <0.0001 |
| Time to First Symptomatic Skeletal Event | 0.712 | 0.539–0.940 | 0.0081 |
| Time to Initiation of Subsequent Antineoplastic Therapy | 0.388 | 0.328–0.458 | <0.0001 |
| Time to Worsening of Disease-Related Physical Symptoms | 1.043 | 0.894–1.217 | 0.7073 |
| Time to Initiation of Opioid Use for ≥7 Consecutive Days | 0.688 | 0.523–0.906 | 0.0037 |
Time to Castration-Resistant Prostate Cancer
Hazard ratio
95% CI: 0.302–0.421 · P < 0.0001
The HR of 0.357 corresponds to a lower estimated instantaneous hazard of the first castration-resistant prostate cancer event in the darolutamide-containing group under the fitted model. The confidence interval is entirely below 1, and the registry reports a one-sided p-value of <0.0001.
Time to Pain Progression
Hazard ratio
95% CI: 0.660–0.950 · P = 0.0058
The reported HR is below 1, indicating a lower estimated hazard of pain progression in the darolutamide-containing group under the analysis model. The confidence interval provides the uncertainty around that relative effect estimate.
Symptomatic Skeletal Event Free Survival
Hazard ratio
95% CI: 0.516–0.718 · P < 0.0001
SSE-FS was defined as a time-to-event outcome involving the first occurrence of a symptomatic skeletal event or death from any cause, whichever occurred first. An HR below 1 therefore represents a lower estimated hazard of reaching this composite endpoint in the darolutamide-containing group.
Time to First Symptomatic Skeletal Event
Hazard ratio
95% CI: 0.539–0.940 · P = 0.0081
The HR of 0.712 indicates a lower estimated hazard of the first symptomatic skeletal event in the darolutamide-containing group under the reported model. This endpoint differs conceptually from SSE-FS because SSE-FS includes death from any cause as part of the event definition.
Time to Initiation of Subsequent Antineoplastic Therapy
Hazard ratio
95% CI: 0.328–0.458 · P < 0.0001
The HR of 0.388 indicates a substantially lower estimated instantaneous hazard of initiation of the first subsequent systemic antineoplastic therapy in the darolutamide-containing group under the reported Cox model. This is a treatment-pathway endpoint rather than a direct measure of survival.
Time to Worsening of Disease-Related Physical Symptoms
Hazard ratio
95% CI: 0.894–1.217 · P = 0.7073
This estimate is above 1 rather than below 1. The 95% CI spans 1, and the reported p-value is 0.7073. Thus, within this posted analysis, the estimate does not provide evidence of a statistically detectable lower hazard for this endpoint under the specified superiority testing framework.
Time to Initiation of Opioid Use for ≥7 Consecutive Days
Hazard ratio
95% CI: 0.523–0.906 · P = 0.0037
The HR of 0.688 indicates a lower estimated hazard of the first opioid use for at least 7 consecutive days in the darolutamide-containing group under the reported model.
8. Endpoints and Time Frames
The registry lists 17 posted outcome measures, with two registered primary endpoints and the formal analyses summarized above. The registry text contains shortened time-frame descriptions for several secondary measures; those descriptions are retained here without adding dates or follow-up values not present in the ClinicalTrials.gov record.
| Endpoint | Registry time frame |
|---|---|
| OS From Date of Randomization Until Death From Any Cause - Number of Events | From randomization of the first participant until death from any cause up to 25 OCT 2021 cut-off date; 533 OS events were reached (approximate 59 months) |
| OS From Date of Randomization Until Death From Any Cause - Month | From randomization of the first participant until death from any cause up to 25 OCT 2021 cut-off date; 533 OS events were reached (approximate 59 months) |
| Time to Castration-Resistant Prostate Cancer - Month | From randomization of the first participant to the first occurrence of an CRPC event up to 25 OCT 2021 cut-off date approximately 59 months |
| Time to Pain Progression - Month | From randomization of the first participant to the first occurrence of a pain progression event up to 25 OCT 2021 cut-off date approximately 59 months |
| Symptomatic Skeletal Event Free Survival (SSE-FS) - Month | From randomization of the first participant to the first occurrence of an SSE event or death from any cause, whichever occurred first up to 25 OCT 2021 cut-off date approximately 59 months |
| Time to First Symptomatic Skeletal Event (SSE) - Month | From randomization of the first participant to the first occurrence of an SSE event up to 25 OCT 2021 cut-off date approximately 59 months |
| Time to Initiation of Subsequent Antineoplastic Therapy - Month | From randomization of the first participant to the initiation of first subsequent systemic antineoplastic therapy up to 25 OCT 2021 cut-off date approximately 59 months |
| Time to Worsening of Disease-Related Physical Symptoms - Month | From randomization of the first participant to the first increase in disease-related physical symptoms based on the NCCN-FACT-FPSI-17 questionnaire up to 25 OCT 2021 cut-off date approximately 59 months |
| Time to Initiation of Opioid Use for ≥7 Consecutive Days - Month | From randomization of the first participant to the first opioid use for ≥7 consecutive days up to 25 OCT 2021 cut-off date approximately 59 months |
9. Statistical Methods Explained
Why was a log-rank test used?
The registered primary endpoint is time-to-event overall survival. A log-rank test is designed to compare the event-time distributions of randomized groups while accounting for different follow-up times and censoring. The ARASENS registry specifically reports the log-rank test as its formal comparison method.
What does an HR of 0.675 mean?
It means the estimated instantaneous hazard of death in the darolutamide + docetaxel group was 0.675 times the hazard in the placebo + docetaxel group under the fitted Cox model. It is a relative hazard measure, not an absolute probability and not a statement that every participant experiences the same treatment effect.
Why is the confidence interval important?
The 95% CI of 0.568–0.801 shows the statistical uncertainty surrounding the primary HR estimate. A point estimate alone cannot show how precisely the treatment effect has been estimated. The interval also remains below 1, which is consistent with the reported superiority result.
Why does the p-value not measure effect size?
The p-value evaluates evidence against the null hypothesis under the specified testing framework. It depends on both the observed data and the amount of information available. The HR communicates the estimated relative effect, while the confidence interval communicates precision.
Why was the analysis stratified?
The registry specifies stratification by extent of disease and alkaline phosphatase. Stratified analysis allows the time-to-event comparison to account for these prespecified categories rather than treating all participants as though the distribution of these factors were identical across the analysis.
What does one-sided testing change?
The ARASENS registry explicitly reports a one-sided p-value for the log-rank test. A one-sided test allocates the specified type I error to a directional alternative. Consequently, its p-value should not be interpreted as though it came from an unspecified two-sided test. The reported confidence interval, however, is explicitly two-sided and uses 95% coverage.
Where does Kaplan-Meier estimation fit?
Kaplan-Meier estimation is the standard descriptive framework for displaying and estimating time-to-event survival functions in randomized trials. The registry-reported ARASENS registry data identify the endpoint type and report log-rank and Cox methods, but do not separately identify Kaplan-Meier estimation as a posted statistical-method field. It is therefore useful as a methodological teaching concept without claiming that a specific Kaplan-Meier estimate was reported here.
10. Stratification by EOD and ALP
The primary and secondary analysis notes consistently specify stratification by extent of disease (EOD) and alkaline phosphatase (ALP). This is an important feature of the statistical design because the same stratification structure is carried through the reported log-rank comparisons and Cox regression models.
| Stratification factor | Registered categories |
|---|---|
| EOD | Non-regional lymph nodes metastases only; bone metastases with or without lymph node metastases; visceral metastases with or without lymph node metastases or with or without bone metastases |
| ALP | <ULN vs ≥ULN |
Stratification does not change the basic interpretation of the HR. Rather, it specifies how the randomized treatment comparison is adjusted for the prespecified strata in the survival analysis. The same EOD and ALP structure is reported for the primary and secondary formal analyses reported in the ClinicalTrials.gov record.
11. Understanding the Time-to-Event Framework
All eight posted formal analyses reported in the ClinicalTrials.gov record are time-to-event analyses. This means that the statistical outcome is not merely whether an event occurred, but when the event occurred relative to randomization.
Time origin
The registered definitions use randomization as the starting point for the time-to-event analysis.
Event
Each endpoint has a specific event definition, ranging from death to disease-related, skeletal, symptom, therapy-initiation, and opioid-use events.
Censoring
Time-to-event methods allow participants without an observed event at the analysis cutoff to contribute their available follow-up without being treated as having experienced the event.
Relative effect
The hazard ratio summarizes the relative instantaneous event hazard between the randomized treatment groups under the Cox model.
This framework is especially useful when participants have different amounts of follow-up. A conventional binary analysis at a single time point would discard much of the timing information. Survival analysis instead uses the observed event times and available follow-up.
The survival function is the probability that the event time T exceeds time t. Kaplan-Meier estimation is commonly used to estimate this function, while the log-rank test compares survival distributions and the Cox model estimates a relative hazard.
12. Primary Endpoint Interpretation: Relative vs Absolute Effects
The primary result is reported as a hazard ratio rather than as a median survival time, survival probability at a particular time, or absolute risk difference. These measures should not be treated as interchangeable.
| Measure | What it communicates | ARASENS result reported |
|---|---|---|
| Hazard ratio | Relative instantaneous event hazard under the Cox model | 0.675 |
| 95% CI | Statistical uncertainty around the HR | 0.568–0.801 |
| Log-rank p-value | Evidence against the null under the one-sided testing framework | <0.0001 |
| OS events | Number of observed deaths contributing to the posted primary analysis | 533 |
The ClinicalTrials.gov record does not provide median overall survival, survival probabilities at specified time points, or absolute risk differences. Those measures are therefore not substituted for the reported HR.
A useful way to read the primary result is to keep three questions separate: How large is the estimated relative effect? The HR is 0.675. How precisely is it estimated? The 95% CI is 0.568–0.801. How strong is the statistical evidence under the prespecified test? The one-sided log-rank p-value is <0.0001.
None of those quantities tells us the absolute probability that an individual participant will survive, the probability of cure, or the magnitude of benefit for every patient. Those questions require different estimands and additional data.
13. Secondary Endpoint Interpretation
The secondary results illustrate why a trial should not be reduced to a single hazard ratio. The estimated effects range from HR 0.357 for time to castration-resistant prostate cancer to HR 1.043 for time to worsening of disease-related physical symptoms.
The visual comparison is descriptive rather than a ranking of endpoints. Different endpoints represent different clinical events and therefore should not be interpreted as though their HRs were measurements of the same underlying outcome.
14. Safety Results
The ClinicalTrials.gov record reports serious adverse events by randomized treatment arm as affected participants divided by participants at risk.
| Serious adverse events | Affected / at risk |
|---|---|
| Darolutamide (BAY1841788) + Docetaxel | 306 / 652 |
| Placebo + Docetaxel | 276 / 650 |
Darolutamide arm
306 participants were reported as affected among 652 at risk for the registry-reported serious-adverse-event measure.
Placebo arm
276 participants were reported as affected among 650 at risk for the registry-reported serious-adverse-event measure.
The ClinicalTrials.gov record does not provide a formal statistical comparison, confidence interval, or p-value for these serious adverse-event counts. They should therefore be presented as descriptive safety information rather than converted into an inferential claim that is not contained in the registry data.
15. Analysis Populations and What the Registry Supports
The ClinicalTrials.gov record identifies the randomized design, enrollment, treatment groups, statistical methods, and reported analyses, but they do not provide a complete analysis-population table or detailed definitions of every analysis set.
| Feature | What is supported by the ClinicalTrials.gov record |
|---|---|
| Randomized design | Yes; allocation is listed as randomized. |
| Parallel groups | Yes. |
| Quadruple masking | Yes. |
| Primary endpoint type | Time-to-event. |
| Formal primary analysis | Yes; one primary-endpoint analysis is posted. |
| Hazard-ratio estimate with CI | Yes. |
| Detailed ITT definition | Not provided in the ClinicalTrials.gov record. |
| Detailed per-protocol definition | Not provided in the ClinicalTrials.gov record. |
| Detailed missing-data/imputation strategy | Not provided in the ClinicalTrials.gov record. |
This distinction is important. It is reasonable to explain what an ITT or per-protocol analysis means generally, but it would not be appropriate to assign a specific analysis population to ARASENS without supporting information in the ClinicalTrials.gov record.
16. Missing Data, Censoring, and Follow-Up
Time-to-event analysis naturally involves censoring because participants can reach the analysis cutoff without experiencing the event. The ClinicalTrials.gov record establishes that the endpoints are time-to-event measures and provide the analysis cutoff for the primary OS analysis, but they do not provide a detailed censoring algorithm or missing-data/imputation plan.
That limitation matters when interpreting survival analyses. Censoring is not equivalent to an observed absence of the event for all future time. A censored participant contributes information up to the point at which their event status is no longer observed under the analysis framework.
17. Non-Inferiority, Equivalence, and Superiority
ARASENS is explicitly identified in the ClinicalTrials.gov record as a superiority trial. There is no non-inferiority or equivalence margin reported in the ClinicalTrials.gov record.
Superiority
The statistical objective is to test whether the treatment effect favors the darolutamide-containing strategy rather than merely demonstrating that it is not unacceptably worse.
No NI margin reported
The ClinicalTrials.gov record does not provide a non-inferiority margin, so none is introduced into the interpretation.
This distinction is important because an HR below 1 in a superiority analysis has a different inferential context from a non-inferiority analysis. In a non-inferiority trial, the key question is whether the confidence interval excludes the prespecified unacceptable-loss margin. That logic does not apply to the ARASENS result as reported in the registry.
18. Interim Analysis, Factorial Design, and Crossover
The ClinicalTrials.gov record identifies a randomized parallel-group design and do not report a factorial design, crossover component, or interim-analysis procedure.
| Design topic | Information in the ClinicalTrials.gov record |
|---|---|
| Factorial design | Not reported; design model is parallel. |
| Crossover | Not reported in the ClinicalTrials.gov record. |
| Interim analysis | Not reported in the ClinicalTrials.gov record. |
| Alpha-spending method | Not reported in the ClinicalTrials.gov record. |
| Multiplicity hierarchy | Not fully reported in the ClinicalTrials.gov record. |
| Bayesian methods | Not reported; the posted analyses use frequentist log-rank and Cox methods. |
Absence of these details from the ClinicalTrials.gov record should not be interpreted as proof that a protocol did not contain additional statistical provisions. It means only that they are not available in the trial-data extract used for this page.
19. Interpreting the Seven Secondary Hazard Ratios
The secondary analyses demonstrate several important principles of survival-analysis interpretation.
| HR relationship to 1 | Statistical meaning | ARASENS examples |
|---|---|---|
| HR < 1 | Lower estimated event hazard in the darolutamide-containing group | 0.357, 0.388, 0.609, 0.688, 0.712, 0.792 |
| HR approximately 1 | Little estimated relative difference in instantaneous hazard | 1.043 for worsening of disease-related physical symptoms |
| CI includes 1 | The interval includes no relative hazard difference | 0.894–1.217 for worsening of disease-related physical symptoms |
It is tempting to interpret every HR below 1 as interchangeable evidence of "benefit." Statistically, that is too broad. Each endpoint has a different event definition, and the meaning of the HR depends on the clinical event being modeled.
For example, an HR of 0.388 for time to initiation of subsequent antineoplastic therapy describes the relative hazard of a treatment-pathway event. It is not an HR for death. Similarly, an HR of 0.609 for SSE-FS concerns a composite endpoint whose event definition includes either a symptomatic skeletal event or death from any cause.
20. Limitations
- Registry-level detail: The ClinicalTrials.gov record provides the formal statistical analyses and their estimates but do not provide a complete statistical analysis plan.
- Incomplete analysis-population detail: Specific ITT, per-protocol, and safety-population definitions beyond the registry-reported serious-adverse-event denominators are not available in the data provided.
- Censoring details: The ClinicalTrials.gov record identifies time-to-event endpoints but does not provide a complete censoring algorithm.
- Missing-data methods: No specific imputation strategy is reported, so none is attributed to the trial.
- Multiplicity: Eight formal analyses are posted, but the ClinicalTrials.gov record does not give a complete hierarchy or alpha-allocation strategy for the secondary endpoints.
- One-sided testing: The posted p-values are one-sided log-rank p-values. They should not be silently reinterpreted as two-sided values.
- Confidence-interval interpretation: The reported 95% CIs are two-sided and quantify uncertainty around the estimated HR; they do not describe individual-level treatment-effect ranges.
- Proportional hazards: The HR is a Cox-model quantity, and the ClinicalTrials.gov record does not provide a diagnostic assessment of the proportional-hazards assumption.
- Endpoint heterogeneity: The secondary endpoints represent different clinical events and cannot be treated as repeated measurements of a single outcome.
- Safety inference: Serious-adverse-event counts are descriptive in the ClinicalTrials.gov record; no formal comparison is provided for them.
- Missing contextual estimates: Median survival and other absolute time-to-event summaries are not included in the ClinicalTrials.gov record and are therefore not reported here.
21. Why This Trial Matters Statistically
ARASENS is a useful teaching case because it concentrates several core concepts in modern randomized survival analysis within one trial. The same analytical framework is applied across overall survival and multiple secondary time-to-event outcomes, allowing the statistical interpretation to be compared across endpoints without changing the fundamental model structure.
| Statistical concept | How it appears in ARASENS |
|---|---|
| Randomization | Randomized phase 3 parallel-group design |
| Masking | Quadruple masking |
| Time-to-event endpoints | Primary OS and multiple secondary outcomes |
| Log-rank testing | Formal statistical method for the posted analyses |
| Hazard ratio | Primary and secondary effect measure |
| Confidence interval | 95% two-sided intervals around reported HRs |
| One-sided testing | One-sided p-values for the reported log-rank analyses |
| Stratified analysis | EOD and ALP used for stratification |
| Cox regression | Source of reported HRs and confidence intervals |
| Superiority testing | Hypothesis type for the formal analyses |
| Composite time-to-event endpoint | SSE-FS combines SSE and death from any cause |
| Safety reporting | Serious adverse events reported as affected / at risk by arm |
The most instructive feature is the alignment between design and analysis. Randomization creates the treatment comparison; time-to-event methodology preserves information about event timing and censoring; stratification accounts for the specified EOD and ALP categories; the log-rank test supplies the formal comparison; and the Cox model expresses the relative effect as a hazard ratio with an uncertainty interval.
22. A Practical Reading Sequence for the ARASENS Results
A statistically disciplined reading of the primary result can proceed in five steps.
Identify the estimand
The primary outcome is time from randomization until death from any cause.
Identify the effect measure
The treatment effect is expressed as a hazard ratio from a stratified Cox regression model.
Read the point estimate
The reported HR is 0.675, indicating a lower estimated hazard in the darolutamide-containing group under the model.
Read the uncertainty
The 95% CI is 0.568–0.801, describing uncertainty around the HR estimate.
Read the hypothesis test
The one-sided stratified log-rank p-value is <0.0001 under a superiority framework.
This sequence prevents a common statistical error: starting with the p-value and treating it as the main result. The effect estimate and confidence interval should be understood first, with the p-value providing the inferential test specified by the trial.
23. Clinical Interpretation vs Statistical Interpretation
Statistical interpretation
The primary randomized comparison produced an OS HR of 0.675 with a 95% CI of 0.568–0.801 and a one-sided log-rank p-value of <0.0001. The registered hypothesis type was superiority.
Clinical interpretation
The ClinicalTrials.gov record supports describing a difference between the randomized treatment strategies in the reported time-to-event outcomes. The magnitude and meaning of that difference depend on the specific endpoint, while safety is represented separately by the reported serious-adverse-event counts.
These two levels of interpretation should remain distinct. Statistical significance describes evidence under a specified model and testing framework; clinical interpretation requires consideration of the endpoint, treatment context, magnitude of effect, precision, and safety evidence.
24. Statistical Concepts in This Trial
Learn more about the methods used in this trial:
25. Related Statistical Calculators
26. Sources
- ClinicalTrials.gov: ARASENS — NCT02799602.
- PubMed: PMID 36795843.
- PubMed: PMID 35656777.
- PubMed: PMID 35179323.
Continue through the Clinical Biostats statistical pathway
Explore the underlying survival-analysis methods, statistical calculators, and other clinical-trial results.
27. Record Summary
ARASENS provides a clear example of randomized survival analysis in a phase 3 oncology trial. The ClinicalTrials.gov record describes a randomized, parallel, quadruple-masked design with 1306 participants and two registered primary overall-survival measures. The primary formal analysis used a one-sided stratified log-rank test, with the hazard ratio and 95% confidence interval obtained from a Cox regression model stratified by extent of disease and alkaline phosphatase.
The primary OS result was HR 0.675, with a 95% CI of 0.568–0.801 and a one-sided p-value of <0.0001, based on 533 reported OS events at the 25 OCT 2021 cutoff. Seven additional formal secondary time-to-event analyses were also posted, with hazard ratios ranging from 0.357 to 1.043.
The statistically important lesson is that these numbers answer different questions. The hazard ratio describes relative event hazard, the confidence interval describes uncertainty around that estimate, and the p-value describes evidence under the specified hypothesis-testing framework. None alone represents an absolute treatment benefit for an individual participant.