Bone Marrow Transplantation in Young Adults With Severe Sickle Cell Disease: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Bone Marrow Transplantation in Young Adults With Severe Sickle Cell Disease (NCT01565616), a na phase 2 study. The primary outcome is Event -Free Survival Rate.

2. Clinical Question

3. Trial Design

This is a completed Phase II, multi-center, single-group study of hematopoietic stem cell therapy for adults with severe sickle cell disease. The registry lists enrollment of 22 and a single intervention group, Bone Marrow Transplant Recipients. That group is described as adults undergoing transplantation from an HLA-identical sibling donor or an unrelated HLA-matched donor. The study summary describes a two-component design: the first component was restricted to patients with an HLA-identical sibling donor, while the second included patients with a related or unrelated HLA-matched donor.

The protocol description states that 5 patients would be transplanted in the first component. It specified that, if no more than 2 of those first 5 experienced unacceptable toxicity, including death, within the first six months after transplantation, the regimen's safety would be considered promising in adults with sickle cell disease. The second component was intended to include up to 15 additional patients and assess the safety and feasibility of unrelated donor transplantation. These are planned design details; the registry record does not report whether the stated criterion was met or provide results by component.

Data related to study endpoints were to be collected for 1 year after transplantation, with centers encouraged to conduct longer-term follow-up under institutional guidelines. The primary endpoint timeframe is listed as 1 year after transplant. The registry lists the study as completed, with a start of 2012-03 and primary completion of 2016-06-30. It does not report a randomized allocation, masking, or a comparative control arm. Consequently, the study design can describe outcomes among the transplant recipients, but does not by itself provide a concurrent comparison for estimating the effect of transplantation relative to another treatment or no transplantation.

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.

Before assignment: The first component of the study was restricted to 5 patients with a related donor. If no more than 2 of the first 5 patients experienced unacceptable toxicity within six months of transplantation then the safety of the regimen was considered promising and the study could include patients with a related or unrelated HLA matched donor.

Overall Study

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: Individuals with severe sickle cell disease receiving hematopoietic cell transplantation (HCT) from a human leukocyte antigen (HLA)-identical sibling donor or an unrelated HLA-matched donor

6. Primary Endpoint

The registry lists the primary outcome as Event -Free Survival Rate, measured over 1 year after transplant.

The primary endpoint is the event-free survival rate at 1 year after transplant. The registry defines event-free status as stable donor erythropoiesis without new clinical evidence of sickle cell disease. Primary or late graft rejection, disease recurrence, and death are endpoint events. Thus, the endpoint combines evidence about graft function and recurrence with survival; an event can occur through any of the listed pathways.

In general, a composite endpoint can capture several clinically relevant ways in which the intended treatment strategy may fail, rather than focusing on only one outcome. It can also be harder to interpret than a single event type because its overall result depends on which component events occur. The registry definition identifies the components, but the primary endpoint result and component-specific counts are not reported in the registry record. It is therefore not possible to describe the observed event-free survival rate or to determine which components contributed to it from the posted results.

The stated timeframe is 1 year after transplant. That fixed horizon makes the endpoint a summary of outcomes over a defined follow-up period, not a measure of longer-term event-free survival. Although the study summary encourages longer-term follow-up, results from that follow-up are not reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does a single-group design allow?

The registry describes a single-group study with one intervention group. In general, a single-group design can report what happened among participants who received the intervention and can document outcomes over follow-up. It does not provide a contemporaneous control group for estimating how outcomes would have differed under another treatment. Differences from an external benchmark, if one were considered, could reflect differences in participants, care, follow-up, or outcome definitions rather than an intervention effect. No external comparison is reported in the registry record.

The two donor components are described as parts of the study plan. They are not presented as randomized arms. The registry record does not report a comparative analysis between donor categories, or results separately for those components. It would therefore be inappropriate to interpret the planned components as equivalent to an allocation-based treatment comparison.

How should the primary endpoint be read?

The endpoint is a binary status at the stated 1-year timeframe: participants meet the event-free definition or experience at least one of the listed events. In general, a participant-level count can be converted into a rate only when the relevant numerator and denominator and the analysis definition are known. The primary endpoint result is not reported in the registry record, so its observed count or rate cannot be stated. No uncertainty interval for that endpoint is reported either.

In general, a confidence interval describes a range of values compatible with a statistical estimate under the method's assumptions. Its width conveys precision: wider intervals indicate greater uncertainty, while narrower intervals indicate greater precision. Without a reported endpoint estimate and interval, the precision of the primary result cannot be assessed. No p-value or hypothesis-test result for the primary endpoint is reported in the registry record.

What do the adverse-event counts represent?

The registry reports participant counts at risk and affected for serious and other adverse events, together with selected serious-event terms. These counts summarize participants recorded with events; they are not necessarily counts of every event episode. In general, one participant may experience multiple event types, and event categories may overlap. The record does not specify the degree of overlap among the reported groups or terms, so counts should not be summed to create an overall total.

Over-dispersion is a general concern when event data vary more than a simple statistical model expects. It can make uncertainty estimates too small if the model assumes less variability than the data contain. The posted safety information is participant-count based, and the registry record does not report a model for recurrent event counts or an over-dispersion assessment. No model-based inference about recurring event rates should be inferred from the counts alone.

What can be inferred from the planning illustrations?

The sample-size material is described as a planning illustration computed from the observed effect, not as the trial's own design. Its stated assumptions include a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation; the effect to detect is specified as a fraction of the observed effect. This hypothetical two-arm framing differs from the actual single-group study design. Any sample-size values under those assumptions are planning illustrations, not observed power and not evidence that the trial had a particular probability of detecting an effect. The observed effect used for the illustration and the resulting sample-size values are not reported in the registry record.

In general, a sample-size calculation asks how many participants would be needed under chosen assumptions to target a specified operating characteristic. Its answer depends on the assumed effect, variability, significance level, allocation, and analysis method. Changing those assumptions changes the planning result. Such a calculation does not establish the precision or power of a completed study after results are observed, and it cannot replace an observed effect estimate with uncertainty measures. The registry record does not report a trial-specific sample-size justification or statistical plan.

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("Bone Marrow Transplant Recipients")
n      <- c(22)
events <- c(19)
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  Bone Marrow Transplant Recipients  22  19  86.4  65.1  97.1  66.7  95.3  66.4  95.0

11. Multiplicity, Missing Data and Analysis Populations

The registry lists 8 outcome measures and 8 analyses, but the record does not report how the analyses were linked to outcomes, which were prespecified as primary or secondary for statistical testing, or whether any adjustment for multiple comparisons was planned. Multiplicity arises when several hypotheses or outcomes are tested: considering more tests can increase the chance of at least one apparently notable result by chance. In general, methods such as adjusting significance thresholds or controlling an error rate can address that issue, but the registry record does not report a multiplicity strategy. No inferential results are reported for the primary endpoint in the registry record, so there is no reported test result to interpret in light of multiple testing.

The primary endpoint is defined at 1 year after transplant, but the registry record does not report the analysis population, participant-level exclusions, or the handling of missing endpoint assessments. It also does not report how loss to follow-up, incomplete outcome information, or timing differences were handled. In general, missing data can affect an estimate when participants with unobserved outcomes differ from those with observed outcomes. Statistical approaches depend on why information is missing and on assumptions about the unobserved outcomes; those assumptions cannot be identified from the record.

The study summary says endpoint data were to be collected for 1 year and encourages longer-term follow-up, but does not report a detailed analysis plan or a longer-term outcome analysis. The record also does not report whether analyses followed an intention-to-treat, per-protocol, or other defined population. These omissions limit assessment of analysis choices and the robustness of any endpoint estimate. They do not establish that particular methods were or were not used outside what the registry record reports.

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

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: elevated liver enzymes (9.1%), mucositis (9.1%), neurological changes (9.1%), hospitalization due to pericardial effusion (9.1%), hospitalization due to abdominal pain, diarrhea, and bloody stools (4.5%).

For the Bone Marrow Transplant Recipients group, the registry lists 22 participants at risk and 14 affected for serious adverse events. For other adverse events, it lists 22 at risk and 12 affected. The record also reports 2 deaths. These are separate entries in the safety record; the registry does not specify whether participants affected by serious and other adverse events overlap. The counts should therefore not be added together.

The listed serious-event terms and percentages are elevated liver enzymes, 9.1%; mucositis, 9.1%; neurological changes, 9.1%; hospitalization due to pericardial effusion, 9.1%; hospitalization due to abdominal pain, diarrhea, and bloody stools, 4.5%; and hospitalization due to abdominal pain, nausea, vomiting, and elevated liver enzymes, 4.5%. These are registry-reported percentages for the listed terms, not a complete description of the timing, duration, or clinical course of events. The record does not provide detail about overlap between terms or explain how the percentages were calculated. The reported death count does not, by itself, establish whether each death met the primary endpoint definition or how it related to a particular adverse event.

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

The record describes a Phase II, single-group study of transplantation in adults with severe sickle cell disease. It defines a primary endpoint that combines stable donor erythropoiesis and absence of new clinical evidence of sickle cell disease, while treating primary or late graft rejection, disease recurrence, and death as events. The record also reports adverse-event counts and selected serious-event terms. These details show what outcomes the study intended to evaluate and what safety information was entered in the registry.

The registry record does not report the primary endpoint result. It is therefore not possible to state the observed event-free survival rate, how precisely it was estimated, or which endpoint events occurred. The record's adverse-event counts cannot fill that gap: they are not a reported analysis of the defined primary endpoint. The registry also does not report a comparative control group or randomized treatment contrast. The posted information therefore does not establish whether transplantation changes outcomes relative to another treatment or to no transplantation.

In general, an outcome observed after an intervention is not, by itself, proof that the intervention caused that outcome. A control group and appropriate analysis can help distinguish treatment effects from other explanations, although conclusions still depend on design and assumptions. In this study, the single-group design can describe the outcomes recorded for transplant recipients, but it does not offer that concurrent comparison.

The safety entries should likewise be interpreted as descriptive registry reports. They identify affected-participant counts, deaths, and selected terms, but do not establish causation, provide full event-level detail, or describe all longer-term outcomes. The study summary says follow-up data were to be collected for 1 year and encourages longer-term institutional follow-up; longer-term results are not reported in the registry record. Taken together, the available record documents a clinical question and aspects of the observed safety reporting, but leaves the primary outcome and its statistical uncertainty unreported.

14. Why This Trial Matters Statistically

This study raises statistical questions that matter when evaluating transplantation in a population described as having severe sickle cell disease: how to define a meaningful outcome, how to assess safety, and how to interpret results from a single-group design. Its primary endpoint combines graft-related status, recurrence, and death at 1 year after transplant. Stating the endpoint components matters because a composite result can represent different underlying event patterns; component-specific reporting helps readers understand what drives an overall outcome.

The registry also describes a two-component donor plan and a safety criterion for the first component. Such a design makes clear that safety and feasibility were central aims, rather than only a comparison of treatment efficacy. However, the registry record does not report whether the criterion was met, results by component, or the primary endpoint estimate. Those omissions prevent a statistical assessment of the planned decision rule and of the endpoint's precision.

Single-group studies can contribute descriptive evidence about the outcomes and adverse events recorded during treatment and follow-up. Their statistical limitation is the lack of a concurrent comparison: outcome patterns cannot be attributed to the intervention by comparing treated participants with themselves or with an unspecified external group. Transparent reporting of numerators, denominators, follow-up, uncertainty, and analysis populations is especially important in this setting. The record reports some safety counts but not the primary endpoint result or its uncertainty, limiting the conclusions that can be drawn from its posted data.

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 endpoint result, despite defining event-free survival at 1 year after transplant. It also does not report an estimate of uncertainty, the number of participants with each primary endpoint event, or results for endpoint components. As a result, neither the endpoint's magnitude nor its precision can be assessed from the posted record.

The study is single-group and has no randomized control arm. Outcomes among transplant recipients can be described, but there is no concurrent comparison in the registry design to separate treatment effects from other influences. The planned donor components do not resolve this limitation because the record does not present them as randomized comparison groups or report their results separately.

Further detail about outcome ascertainment and analysis is not reported in the registry record. This includes the analysis population, missing endpoint data, exclusions, multiplicity handling, and any detailed statistical plan. The registry reports adverse-event counts and selected serious-event terms, but does not report event timing, duration, overlap, or the relation of each event to the primary endpoint. The study summary encourages longer-term follow-up, but longer-term results are not reported in the registry record.

The record lists enrollment of 22, while the study summary describes planned components of 5 patients and up to 15 additional patients. It does not explain in the reported results how the completed enrollment relates to those component plans or provide a component-level accounting. These reporting gaps constrain interpretation; they do not establish what analyses may have been conducted outside the registry record.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Bone Marrow Transplantation in Young Adults With Severe Sickle Cell Disease — NCT01565616.
• Registry record last updated 2017-11-21; status last verified 2017-10.
• Results first posted 2017-09-29.
• 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 describes a completed Phase II, multi-center, single-group study of bone marrow transplantation for adults with severe sickle cell disease. The stated primary endpoint is event-free survival at 1 year after transplant, defined using stable donor erythropoiesis, absence of new clinical evidence of sickle cell disease, and events including graft rejection, disease recurrence, or death. The study summary describes a two-component donor plan and emphasizes safety and feasibility.

The adverse-event record lists 14 affected participants among 22 at risk for serious adverse events, 12 among 22 at risk for other adverse events, and 2 deaths. Selected serious-event terms are reported with percentages. The primary endpoint result, its uncertainty, detailed analysis populations, missing-data handling, multiplicity approach, and longer-term results are not reported in the registry record. The single-group design supplies no randomized control comparison.