Abiraterone Acetate in Asymptomatic or Mildly Symptomatic Patients With Metastatic Castration-Resistant Prostate Cancer: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Abiraterone Acetate in Asymptomatic or Mildly Symptomatic Patients With Metastatic Castration-Resistant Prostate Cancer (NCT00887198), a randomized phase 3 study. The primary outcome is Overall Survival.

2. Clinical Question

3. Trial Design

This is a phase 3 randomized, double-blind, placebo-controlled study with a parallel-group model. It compares abiraterone acetate plus prednisone with placebo plus prednisone in asymptomatic or mildly symptomatic patients with metastatic castration-resistant prostate cancer. The registry record reports enrollment of 1088 and lists the study as completed. The recorded start date is 2009-04-28, and the primary completion date is 2014-03-31.

Randomization assigns participants to treatment groups in a way intended to make the groups comparable at the start of a trial, on average. A placebo comparator can help distinguish outcomes associated with the assigned combination from outcomes observed with the comparison regimen. The registry record identifies quadruple masking. It does not define which roles were masked, so further detail about masking is not reported in the registry record.

The primary outcome population is the intent-to-treat population. It includes randomized participants classified according to their assigned group, regardless of the treatment actually received. The posted median survival estimates are listed for 546 participants in the abiraterone acetate plus prednisone group and 542 in the placebo group. Those outcome-group figures are not interchangeable with the different denominators listed for adverse events.

Overall survival is the primary outcome. Listed secondary outcomes include time to opiate use for prostate cancer pain, time to initiation of cytotoxic chemotherapy, time to deterioration in ECOG performance score by >=1 point, time to PSA progression, treatment-emergent adverse events, and abiraterone plasma concentration measures. The registry record lists 11 outcome measures and 9 posted secondary outcomes. A detailed protocol, planned allocation ratio, and statistical analysis plan are not reported in the registry record.

4. Participant Flow and Accounting

The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.

Randomized Period

Reasons for not completing this period:

Cross Over (Placebo to AA)

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Intent-to-treat (ITT) population included all the randomized participants who were classified according to their assigned treatment group, regardless of the actual treatment received.

5. Baseline Characteristics

The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.

6. Primary Endpoint

The registry lists the primary outcome as Overall Survival, measured over From randomization (Day 1) up to end of study (Month 60).

Overall survival is the time from randomization to death from any cause. The registry record describes the primary outcome as median overall survival in months, measured from randomization (Day 1) up to end of study (Month 60). The median is a time-to-event summary: it identifies the point in the observed survival distribution at which the estimated proportion remaining alive reaches the midpoint. It is not the average survival time and does not describe the outcome for every participant.

Overall survival is used as a time-to-event endpoint because it captures the time until a clearly defined event, regardless of the cause of death. Participants who have not experienced the event by the end of their observed follow-up contribute information up to that point rather than being treated as if they had died. This is called censoring, a general feature of time-to-event analysis. The record does not describe censoring rules or the method used to estimate the medians, so those details are not reported in the registry record.

The posted median is 34.66 months for abiraterone acetate plus prednisone, with a 95% confidence interval of 32.72 to 36.8 months. For placebo, the median is 30.29 months, with a 95% confidence interval of 28.65 to 33.28 months. A median and its confidence interval summarize each group separately; by themselves, they are not a formal estimate or test of the difference between groups.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

Time-to-event methods are designed for outcomes recorded as the time until an event, such as death. They can use information from participants who experience the event as well as participants whose follow-up ends without the event being observed. In the latter case, the observation is censored: it contributes information up to the last point at which the participant's status is known. This is a general explanation of the method, not a claim about the exact censoring procedures used in this study. Those procedures are not reported in the registry record.

What does a median survival estimate describe?

The median survival is a feature of the estimated survival distribution. It marks the time at which the estimated probability of remaining alive reaches the midpoint. It is useful as an interpretable summary of the timing of an event, but it compresses a curve of survival experience into a single time value. It does not show the full pattern of events over follow-up, and it does not indicate whether the groups differ consistently throughout follow-up.

The posted medians are 34.66 months for abiraterone acetate plus prednisone and 30.29 months for placebo. The registry record reports a 95% confidence interval of 32.72 to 36.8 months for the former and 28.65 to 33.28 months for the latter. A confidence interval characterizes uncertainty in the estimated median under the estimation method. Its width can reflect the amount and timing of information available, among other things. The specific estimation procedure and any assumptions used to construct these intervals are not reported in the registry record.

Why is the hazard ratio not interchangeable with the median?

A hazard is an event rate at a particular point in follow-up among participants still at risk at that time. A hazard ratio compares hazards between groups over follow-up under the model used. It is not a comparison of median times, and it does not directly state how many months longer participants live. If the relative event rate changes over time, a single hazard ratio may not represent the whole pattern well. Assessing that issue requires information about the model and its assumptions.

The registry record does not report a hazard ratio, its confidence interval, or a p-value for the primary outcome. It also does not describe a survival model or a test of the difference between groups. Therefore, an interpretation should not infer those quantities from the medians or their separate confidence intervals. The posted values permit a descriptive reading of each group's median and uncertainty, but not reconstruction of the sponsor's primary comparative analysis.

What does randomization contribute?

Randomization is intended to create comparable groups at the time treatment is assigned, reducing the risk that measured or unmeasured baseline characteristics systematically determine group assignment. The trial is described as randomized, double-blind, and placebo-controlled. The record says masking was quadruple but does not identify the roles involved. Randomization supports a comparative design; it does not itself guarantee complete follow-up, correct measurement, or unbiased analysis if important departures from the planned conduct occur.

The primary population is intent-to-treat: participants are analyzed according to assigned group regardless of treatment actually received. In general, this approach preserves the randomized assignment contrast and reflects the effect of being assigned to a treatment strategy. It is distinct from an analysis based only on treatment received, which can be affected by post-randomization decisions. The record does not describe any additional analysis populations.

How should sample-size illustrations be understood?

The planning illustrations associated with the posted results use the observed effect as a reference and assume a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. They are illustrations of planning scenarios, not observed power and not a substitute for the study's original design calculations. For time-to-event outcomes, the stated convention is to express planning quantities as total events; for other outcomes, it is participants per arm. The registry record does not report the trial's own sample-size justification or the assumptions used to design the study.

In general, a sample-size calculation asks how much information a planned study would need to detect a specified effect under stated assumptions. A smaller target effect generally requires more information than a larger target effect, all else equal. That general relationship should not be mistaken for a description of this trial's planning. The record does not report the study's target effect, planned event count, or original power calculation.

Why does the analysis plan matter?

Statistical methods establish how outcomes are summarized, how uncertainty is quantified, how comparisons are made, and how incomplete observations are handled. Prespecification helps readers distinguish planned analyses from choices made after results are known. The registry record does not report a detailed statistical analysis plan, interim analyses, model specifications, or multiplicity procedures. These absences limit how specifically the posted summary can be assessed, but do not change the meaning of the values that are reported.

10. Multiplicity, Missing Data and Analysis Populations

The registry record lists 11 outcome measures and 9 posted secondary outcomes. The listed outcomes address several domains, including overall survival, pain-related opiate use, initiation of cytotoxic chemotherapy, ECOG performance score, PSA progression, treatment-emergent adverse events, and abiraterone plasma concentrations. Testing or estimating many outcomes raises a general multiplicity concern: the more statistical comparisons considered, the greater the chance that some results may appear notable by chance if no adjustment or interpretation strategy is specified. No multiplicity adjustment or hierarchy of secondary outcomes is reported in the registry record.

The record does not report a detailed statistical analysis plan, interim analyses, or a missing-data strategy. For time-to-event outcomes, censoring is often used when an event is not observed during a participant's available follow-up; the specific rules and assumptions for this trial are not reported in the registry record. The status of participants with incomplete outcome information is also not described. It is therefore not possible to assess from the registry record how missing observations were handled or whether sensitivity analyses were conducted.

The primary outcome population is the intent-to-treat population, defined as all randomized participants classified according to assigned group, regardless of actual treatment received. That definition is reported, but the record does not describe additional analysis populations or the details of any deviations from assigned treatment. It also does not report a primary comparative estimate or test. These omissions leave important aspects of the inferential analysis unclear, even though the two group-specific median survival estimates and confidence intervals are posted.

11. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 5% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: disease progression (6.5%), urinary tract infection (5.4%), haematuria (3.2%), pulmonary embolism (2.2%), fatigue (2.2%).

The serious adverse event figures are counts of affected participants alongside the number listed as at risk for each group. For abiraterone acetate plus prednisone, 215 participants were affected among 542 at risk; for placebo, 156 were affected among 540 at risk. A separate group labelled Placebo to AA lists 40 affected among 93 at risk. That group is distinct in the adverse-event record and should not be treated as another randomized comparison arm without further information, which is not reported in the registry record.

The listed serious adverse event terms include Disease Progression at 6.5%, Urinary Tract Infection at 5.4%, Haematuria at 3.2%, Pulmonary Embolism at 2.2%, Fatigue at 2.2%, and Cellulitis at 2.2%. These percentages describe the listed terms in the registry record; the record does not provide further detail about their coding, timing, or overlap among participants.

Counts of affected participants do not convey event severity, duration, causality, or how many events each participant experienced. The different at-risk denominators also mean the counts should be read with their corresponding group labels. Death counts are not reported in the adverse-event figures, and details of the safety analysis population are not reported in the registry record.

12. What the Result Does, and Does Not, Mean

The posted primary outcome describes median overall survival in the two assigned groups. The reported medians are 34.66 months for abiraterone acetate plus prednisone and 30.29 months for placebo, each with a 95% confidence interval. These values summarize the estimated time-to-death distributions for the intent-to-treat population, where death from any cause is the event.

The medians are not a full account of survival throughout follow-up, and they are not a formal between-group effect estimate. They do not provide a hazard ratio, a p-value, or a direct estimate of the uncertainty in the comparison. Those comparative statistics are not reported in the registry record. The estimates should therefore be read as group-specific summaries, not as a complete statistical conclusion about the trial's primary question.

The trial's randomized, double-blind, placebo-controlled design is relevant to how the comparison was intended to work. However, the record does not provide the detailed analysis plan, handling of missing data, or model assumptions needed to evaluate the primary comparison fully. The record's intent-to-treat definition clarifies how participants were classified for the primary outcome, but does not describe adherence, treatment changes, or follow-up completeness.

The safety counts and secondary outcome listings answer different questions from overall survival. Counts of participants with serious adverse events do not establish whether events were caused by treatment, and listed secondary outcomes cannot be assumed to have the same analysis population or method as the primary endpoint. The registry record does not report a multiplicity strategy for secondary outcomes.

Accordingly, the posted record supports a careful description of the reported survival medians, their confidence intervals, and the recorded safety counts. It does not support a complete reconstruction of the primary statistical test or a comprehensive assessment of all outcomes. No treatment recommendation follows from these summaries alone.

13. Why This Trial Matters Statistically

This trial provides a useful example of the distinction between reporting group-specific time-to-event summaries and reporting a direct treatment comparison. Median overall survival and its confidence interval are understandable summaries, but they do not replace a comparative estimate such as a hazard ratio with its uncertainty, or a clearly described test. The registry record reports the medians and intervals but does not report those comparative statistics for the primary outcome.

The design also illustrates why analysis population definitions matter. The primary endpoint is described for an intent-to-treat population, with participants classified by randomized assignment regardless of treatment received. This preserves the assigned-group comparison as the basis for interpretation, while leaving questions about treatment changes and missing follow-up unanswered when those details are not reported.

Another statistical issue is the relationship between a registered set of outcomes and the outcomes with posted results. The registry lists 11 outcome measures and 9 posted secondary outcomes. Without a reported multiplicity strategy or analysis hierarchy, readers cannot determine how the secondary outcomes were prioritized or how their uncertainty should be interpreted across the set.

Finally, the posted confidence intervals illustrate that precision is part of the result, not an optional qualification. The intervals communicate uncertainty about each median, while the lack of a reported comparative interval leaves uncertainty about the treatment contrast unquantified in the registry record. This distinction is central to reading clinical trial results responsibly: descriptive estimates, inferential comparisons, and analysis-plan details each contribute different information.

14. Limitations

• The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
• Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.

The registry record does not include a hazard ratio, confidence interval for a treatment contrast, or p-value for the primary outcome. It reports group-specific medians and confidence intervals, but those summaries do not establish the result of a formal comparison. The record also does not state the survival estimation method, comparative model, censoring rules, or assumptions used in the primary analysis.

Details needed to assess the completeness and conduct of follow-up are not reported in the registry record. This includes the missing-data strategy, the handling of participants with incomplete outcome information, and the results of any sensitivity analyses. The intent-to-treat population is defined, but further analysis populations and the extent of treatment changes or departures from assigned treatment are not described.

The registry record lists secondary outcomes but does not report a multiplicity procedure or hierarchy for interpreting them. It lists 11 outcome measures and 9 posted secondary outcomes, so the available record does not provide a complete account of all listed outcome results. The statistical analysis plan and interim analyses are not reported.

The serious adverse event figures include affected-participant counts for groups with different at-risk denominators, including a group labelled Placebo to AA. The record does not explain the relationship of that group to the randomized comparison or provide detailed information about event timing, coding, or attribution. Death counts are not reported in the adverse-event summary. These limitations constrain interpretation of both the comparative survival evidence and the safety counts.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Abiraterone Acetate in Asymptomatic or Mildly Symptomatic Patients With Metastatic Castration-Resistant Prostate Cancer — NCT00887198.
• Registry record last updated 2025-02-04; status last verified 2025-01.
• Results first posted 2015-04-09.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

18. Record Summary

The registry record describes NCT00887198 as a completed phase 3 randomized, double-blind, placebo-controlled, parallel-group study of abiraterone acetate plus prednisone versus placebo plus prednisone. It enrolled 1088 patients with asymptomatic or mildly symptomatic metastatic castration-resistant prostate cancer. The recorded start date is 2009-04-28, and the primary completion date is 2014-03-31.

The primary endpoint is overall survival, defined as time from randomization to death from any cause, in the intent-to-treat population. The posted median is 34.66 months for abiraterone acetate plus prednisone, with a 95% confidence interval of 32.72 to 36.8 months; for placebo, it is 30.29 months, with a 95% confidence interval of 28.65 to 33.28 months.

The record does not report a hazard ratio, primary-outcome p-value, detailed statistical analysis plan, missing-data strategy, or multiplicity procedure. It lists 11 outcome measures and 9 posted secondary outcomes. Serious adverse event counts and selected event terms are also recorded, but the details needed for a complete comparative safety interpretation are not reported in the registry record.