Optimizing Haploidentical Aplastic Anemia Transplantation (BMT CTN 1502): Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Optimizing Haploidentical Aplastic Anemia Transplantation (BMT CTN 1502) (NCT02918292), a na phase 2 study. The primary outcome is Percentage of Participants With Overall Survival (OS).

2. Clinical Question

3. Trial Design

This is a prospective, multicenter phase II study of haploidentical transplantation for severe aplastic anemia. The registry lists the study as completed, with an enrollment of 32 participants. It describes one treatment group, called Haplo Bone Marrow HSCT, rather than separate randomized arms. Allocation is listed as not applicable and masking as none.

The study’s primary objective was to assess overall survival at 1 year after hematopoietic stem cell transplantation. The primary outcome description specifies that the analysis population includes transplanted participants. The registry does not report how many enrolled participants underwent transplantation, so the size of that endpoint analysis population is not available in the record.

The described preparative regimen includes antithymocyte globulin, fludarabine, cyclophosphamide and low-dose total body irradiation before haploidentical transplantation. The registry also lists post-transplant cyclophosphamide, tacrolimus, mycophenolate mofetil and G-CSF among the interventions; the complete treatment details are not reported in the registry record. The study’s secondary outcomes include neutrophil and platelet recovery, sustained engraftment, graft-failure-free survival, graft failure, autologous recovery and acute graft-versus-host disease.

A single-group design can describe outcomes among participants receiving the study approach, but it does not provide a concurrent control group for a direct treatment comparison. The registry record does not report a statistical analysis plan, sample-size justification, interim analyses or a comparator-based hypothesis test. The enrollment of 32 should not be read as evidence of a particular power or as the number included in every outcome analysis.

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.

Study Enrollment Prior to Transplant

Reasons for not completing this period:

Study Follow up After Transplant

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Analysis Population includes transplanted participants.

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.

Population: Baseline Analysis Population includes transplanted participants.

6. Primary Endpoint

The registry lists the primary outcome as Percentage of Participants With Overall Survival (OS), measured over 1 year.

The primary endpoint is the percentage of participants with overall survival at 1 year. The registry defines the time-to-event measure as the interval from transplant to death from any cause, last follow-up or 1 year from transplant, whichever occurs first. Thus, death from any cause is the event; last follow-up and the one-year limit determine the end of observation for participants who have not had that event by then.

Overall survival is a broad endpoint because it counts death from any cause rather than requiring a particular cause of death. For a transplant study, it gives a summary of survival over the defined follow-up period. It does not by itself describe engraftment, graft failure, complications or the reason for any death; those require separate outcomes and supporting detail.

The registry states that the one-year survival probability and its 95% confidence interval were estimated with the Kaplan-Meier estimator and Greenwood’s formula. In general, a confidence interval conveys uncertainty around an estimated quantity, while the Kaplan-Meier method uses event timing and accounts for participants whose observation ends before an event is recorded. The estimate and interval themselves are not reported in the registry record, so the precision and observed one-year survival cannot be assessed from this record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The primary endpoint is a time-to-event outcome. In general, time-to-event methods use both whether an event occurred and when it occurred. Here, the event is death from any cause, measured from transplant. The registry limits the endpoint observation at 1 year and also identifies last follow-up as an endpoint time, whichever occurs first. This defines the time window but does not provide the observed event times or the number of participants followed to each point.

What does the Kaplan-Meier estimator do?

In general, the Kaplan-Meier estimator estimates the probability of remaining free of the event over time. It updates the estimated survival probability as events occur, using the participants still under observation at each event time. Participants whose follow-up ends without a recorded event can contribute information up to the time their observation ends. This is often called censoring. The method does not require every participant to have the same length of follow-up, but its interpretation depends on appropriate handling of follow-up and censoring.

For this study, the registry says that the one-year overall-survival probability was estimated with the Kaplan-Meier method. It does not report the estimate, the event-time data, the number at risk over time, or details of how loss to follow-up was handled. The endpoint description identifies last follow-up as a time limit, but it does not tell readers how many participants had follow-up ending before 1 year or why. Those details would help assess how much information supports the one-year estimate.

What does Greenwood’s formula contribute?

In general, Greenwood’s formula estimates the variance of a Kaplan-Meier survival estimate. That variance is used to quantify uncertainty and construct a confidence interval. The registry names Greenwood’s formula and specifies a 95% confidence interval for the primary endpoint. A confidence interval is an uncertainty range around an estimate, not a guarantee that the true value lies within a particular interval. Its width depends on the available information and the event and censoring pattern. Since neither the estimate nor its interval is reported, the registry record does not permit evaluation of the precision of the primary result.

What can a single-group design establish?

In general, a single-group study can describe outcomes observed among people receiving a study approach. It does not create a randomized control group, which is one way to balance known and unknown participant characteristics across treatment groups. This study is listed as single group, with allocation not applicable and no masking. The record therefore describes an outcome-estimation objective, not a randomized comparison. Even if a survival estimate were reported, the design alone would not show what the survival outcome would have been for the same participants under another treatment.

The study is identified as phase II and prospective, and its summary describes it as multicenter. These labels describe the study’s stage and general design, but do not specify its analysis methods beyond those stated for the primary endpoint. A phase label does not, by itself, establish the target effect, statistical power, or a particular decision threshold. A sample-size justification is not reported in the registry record, and the enrollment figure should not be interpreted as an observed-power calculation.

What is not described about the analysis?

The registry lists 20 outcome measures and no analysis entries. The record does not report a fuller statistical analysis plan, such as covariate adjustment, subgroup analyses, alternative endpoint definitions, or a method for handling missing endpoint information. It also does not report interim analyses. These items should not be inferred from the use of Kaplan-Meier estimation and Greenwood’s formula; those methods specify the stated survival estimation and uncertainty approach, not every analysis choice.

In general, a statistical method can be appropriate to an endpoint while the record still lacks enough detail to assess its implementation. For example, readers would need the number transplanted, the number of deaths included in the endpoint analysis, the follow-up distribution and the reported estimate with its confidence interval to understand the result. Those details are not reported in the registry record. The registry’s description supports explaining how the endpoint was intended to be estimated, but not reconstructing an estimate or judging its numerical precision.

10. Exact Estimates for Each Arm

No two-arm comparison is shown for this trial, but each arm's result can still be summarized with exact interval estimates computed from the posted counts. The Clopper-Pearson interval is exact and conservative; the Wilson interval is a common closer-to-nominal alternative; the Bayesian credible interval uses a uniform Beta(1, 1) prior. For small groups the three can differ noticeably.

R code and output

arm    <- c("Haplo Bone Marrow HSCT")
n      <- c(31)
events <- c(25)
for (i in seq_along(n)) {
  ci <- binom.test(events[i], n[i])$conf.int          # Clopper-Pearson exact interval
  cr <- qbeta(c(0.025, 0.975), 1 + events[i], 1 + n[i] - events[i])   # Bayesian, uniform Beta(1,1) prior
  wi <- (function(x, n) { p <- x / n; z <- qnorm(0.975); d <- 1 + z^2 / n
    c((p + z^2 / (2 * n) - z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d, (p + z^2 / (2 * n) + z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d) })(events[i], n[i])
  cat(sprintf("ARM|%s|%d|%d|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f\n", arm[i], n[i], events[i], 100 * events[i] / n[i],
              100 * ci[1], 100 * ci[2], 100 * wi[1], 100 * wi[2], 100 * cr[1], 100 * cr[2]))
}

ARM  Haplo Bone Marrow HSCT  31  25  80.6  62.5  92.5  63.7  90.8  63.6  90.7

11. Multiplicity, Missing Data and Analysis Populations

The registry lists 20 outcome measures, including the primary overall-survival endpoint and secondary outcomes related to blood-cell recovery, engraftment, graft failure, autologous recovery and acute graft-versus-host disease. When a study evaluates multiple outcomes, there can be more opportunities for apparently notable findings to arise by chance. In general, a prespecified hierarchy or multiplicity adjustment can help explain how multiple statistical questions are interpreted. The registry record does not report a multiplicity strategy, so it is not possible to determine whether or how the secondary outcomes were adjusted or prioritized beyond identifying overall survival as the primary endpoint.

The record states that the primary analysis population includes transplanted participants. It does not report the number transplanted or provide analysis denominators for the primary endpoint and each secondary outcome. The enrolled population is listed as 32, but it should not be assumed that all enrolled participants contributed to every endpoint.

The primary endpoint definition includes last follow-up as a time limit, and the stated method is Kaplan-Meier estimation. In general, time-to-event methods can account for participants whose observation ends before the event, but that does not describe all forms of missing data or establish why follow-up ended. The registry does not report how missing outcome information, incomplete follow-up or other unavailable measurements were handled. It also does not describe sensitivity analyses for missing data.

These are limits of the registry record’s reporting. They do not establish that a particular analysis or missing-data procedure was or was not used outside the information recorded in the registry.

12. Safety Results

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

Deaths

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

Most frequent serious adverse event terms

Serious events with the highest arm-level rate: incarcerated inguinal hernia (3.1%).

For the enrolled-participant group, the registry lists 32 participants at risk for serious adverse events and 1 affected participant. It lists 32 at risk for other adverse events and 0 affected participants. The same group has 7 deaths listed. The most frequently listed serious-event term is incarcerated inguinal hernia, reported at 3.1%.

These entries are aggregate safety counts. They do not describe when the events occurred, their duration, their clinical course or whether they were judged related to transplantation or another intervention. The registry record also does not clarify the relationship between the deaths and the serious adverse-event count. Deaths should not be interpreted as occurring within the primary one-year endpoint window without timing information.

The adverse-event counts are not the same as the primary overall-survival estimate. That estimate was described as a Kaplan-Meier probability using the transplanted analysis population and follow-up from transplant; the safety group is identified as enrolled participants. The record does not provide the data needed to reconcile these populations or calculate a survival probability from the listed death count. The listed serious-event term and percentage describe the registry entry, not a comparison with another group or proof of causation.

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

The registry record establishes that the study was a completed, prospective, multicenter phase II study of haploidentical transplantation in severe aplastic anemia, with an enrollment of 32 participants. It also describes overall survival at 1 year after transplantation as the primary endpoint and specifies Kaplan-Meier estimation with a 95% confidence interval calculated using Greenwood’s formula.

However, the numerical primary endpoint result is not reported in the registry record. There is no reported one-year survival probability or confidence interval from which to describe the observed outcome or its precision. The study’s completed status and enrollment count do not fill that gap. Nor can the 7 deaths listed in the safety information be used as a substitute: their timing and relationship to the transplanted primary analysis population are not reported.

The single-group design also limits what any outcome can establish. A result from this study would describe outcomes among participants receiving the study approach. It would not, on its own, quantify a difference from another treatment or show what would have happened to the same participants under an alternative approach. There is no concurrent comparator group described in the registry record.

The secondary outcome list indicates that recovery, engraftment, graft failure and acute graft-versus-host disease were also of interest. Yet the registry record does not provide numerical results for those outcomes or a statistical analysis plan for interpreting them. The listed adverse-event figures offer limited descriptive safety information, without timing, attribution or outcome-level detail.

Accordingly, the record supports a description of the research question, design and planned survival method, but not a conclusion about the observed one-year survival probability, its precision or comparative effects. Missing numerical outcome results should be treated as unavailable in the registry record, rather than interpreted as favorable or unfavorable findings.

14. Why This Trial Matters Statistically

This study raises a useful statistical question because overall survival is a time-to-event endpoint, while the study is described as a prospective, multicenter phase II evaluation of a single treatment group. The endpoint requires attention not only to whether deaths occurred but also to their timing and to how long participants remained under observation. The registry’s choice of Kaplan-Meier estimation reflects that time-based structure.

The stated use of Greenwood’s formula and a 95% confidence interval is also important to interpretation. Reporting an estimate together with its uncertainty would help readers distinguish the point estimate from the precision supported by the observed data. In this record, the method is named but the estimate and interval are not reported. That makes the gap between specifying an analysis and publishing a result especially clear.

The distinction between enrolled participants and the transplanted analysis population matters as well. The registry reports 32 enrolled participants but does not report the number transplanted. For an endpoint measured from transplant, the denominator and follow-up information are central to understanding the analysis. Without them, readers cannot determine how the enrolled group relates to the primary endpoint population.

Finally, the single-group design shapes the interpretation. It can describe outcomes under the study approach, but it does not provide a randomized comparison. This statistical distinction is separate from the clinical context: a survival estimate, if reported, would answer a descriptive question about this group, not establish a causal difference from an unobserved alternative. The record is therefore useful for identifying the endpoint and design, while its missing numerical outcome limits what can be concluded from the posted information.

15. 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 most direct limitation is that the registry record does not report the primary one-year overall-survival estimate or its 95% confidence interval. It also does not report the number transplanted, the endpoint event count or the number with follow-up through the defined period. These omissions prevent assessment of the primary result and the information supporting it.

The record lists 32 enrolled participants, but the primary endpoint population is described as transplanted participants. Without the transplanted count or endpoint denominators, enrollment alone does not establish the analysis size. The 7 deaths in the adverse-event information do not resolve this limitation because timing and membership in the primary analysis population are not reported.

The study is single group, with no comparator described. Any outcome would therefore lack a concurrent randomized contrast in this record. The registry also does not report a statistical analysis plan, a sample-size justification, interim analyses or a multiplicity strategy. Although 20 outcome measures are listed, numerical results and analysis details are not posted in the record.

Follow-up handling is only partly described. The endpoint definition uses death, last follow-up or 1 year from transplant, whichever occurs first, but the registry does not provide follow-up distributions, reasons for follow-up ending or sensitivity analyses. The safety entries likewise lack event timing and attribution details. These limitations concern what the registry record reports; they do not establish what information may have been collected or analyzed elsewhere.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Optimizing Haploidentical Aplastic Anemia Transplantation (BMT CTN 1502) — NCT02918292.
• Registry record last updated 2026-03-31; status last verified 2026-03.
• Results first posted 2022-07-12.
• 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.

19. Record Summary

The registry record describes NCT02918292, Optimizing Haploidentical Aplastic Anemia Transplantation (BMT CTN 1502), as a completed, prospective, multicenter phase II single-group study in severe aplastic anemia. Enrollment is listed as 32. The study’s primary objective was to assess overall survival at 1 year after hematopoietic stem cell transplantation.

The primary endpoint is defined from transplant to death from any cause, last follow-up or 1 year from transplant, whichever occurs first. The registry states that the one-year probability and 95% confidence interval were estimated using the Kaplan-Meier estimator and Greenwood’s formula. The primary analysis population is transplanted participants.

The registry record does not report the numerical primary survival result or confidence interval, the number transplanted, or outcome analysis details. It lists 20 outcome measures and no analysis entries. Safety information for enrolled participants includes 1 affected participant with a serious adverse event, 0 affected participants with other adverse events, and 7 deaths; incarcerated inguinal hernia is listed as the leading serious-event term at 3.1%.