Busulfan Safety/Efficacy as Conditioning Prior to Hematopoietic Cell Transplantation (HCT): Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Busulfan Safety/Efficacy as Conditioning Prior to Hematopoietic Cell Transplantation (HCT) (NCT00361140), a non-randomized phase 4 study. The primary outcome is Non-relapse Mortality.

2. Clinical Question

The study was designed to escalate busulfan exposure while using AUC measurements to guide dose adjustment. Its stated purpose was to determine a maximally tolerated level or AUC and evaluate the potential therapeutic benefit of higher busulfan doses. The posted record therefore concerns both dose delivery and clinical outcomes in the transplant-conditioning setting, but the reported primary endpoint is a count of non-relapse deaths, not a direct measure of busulfan exposure or transplant success.

The scientific question is distinct from whether busulfan is better than an alternative conditioning regimen. With a single-group, non-randomized design and no control arm, the record cannot provide a randomized treatment contrast. It can describe outcomes observed across dose levels, but comparisons across those levels are not protected from differences in participant characteristics, timing, or other influences. The registry record does not report additional information about these factors or a statistical comparison between levels.

3. Trial Design

This was a Phase 4, non-randomized, single-group study with no masking. The registry lists enrollment of 72 participants and the status as completed. The study began in 2005-08, and primary completion was recorded in 2012-02. The sponsor was H. Lee Moffitt Cancer Center and Research Institute.

The conditioning regimen combined fludarabine with busulfan administered on days -6, -5, -4, and -3 relative to transplant. Day 0 was defined as the day of hematopoietic progenitor cell reinfusion. Blood samples were to be collected so that busulfan doses could be modified according to AUC levels. Supportive care was described as following institutional guidelines.

The registry describes three busulfan exposure levels: AUC Level 1, 6000 +/- 600 uM-min; AUC Level 2, 7500 +/- 750 uM-min; and AUC Level 3, 9000 +/- 900 uM-min. Each level also included fludarabine 40mg/m2 IV over 1 hour. The dose-escalation objective was to identify the maximally tolerated level or AUC. The registry record does not report the specific rules used to move between levels, the definition of dose-limiting toxicity, or whether a formal stopping rule was used.

Because allocation was non-randomized and the model was single-group, the dose levels do not constitute randomized treatment arms or a control-versus-treatment comparison. The registry record does not report whether dose levels were enrolled sequentially, whether any participants changed dose level, or the timing of accrual within each level. Those details matter when interpreting group sizes and outcomes. The reported at-risk group sizes for serious adverse events differ by level, but the record does not explain why. The design is best read as dose escalation with observed outcomes, rather than as a trial estimating a causal contrast between independently assigned regimens.

The study addressed participants with several hematologic conditions, including myelodysplastic syndromes, myeloproliferative disorders, lymphocytic leukemia, myeloma, and lymphoma. The registry does not provide condition-specific enrollment or outcome results in the information available for this 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.

Before assignment: candidates not meeting eligibility criteria excluded.

Overall Study

Analysis population for the primary outcome, as defined in the registry: Intent to treat

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 Non-relapse Mortality, measured over 100 days.

The primary endpoint is non-relapse mortality, defined in the registry as the number of participants who died from causes unrelated to relapse within the first 100 days after transplant. The endpoint is reported as a participant count, and the specified analysis population is intent to treat. The registry record does not report the observed count.

Non-relapse mortality is used to describe deaths after transplant that are not attributed to relapse of the underlying disease. In a conditioning study, it captures a clinically consequential outcome that may occur during the early post-transplant period. As a count, it is straightforward to interpret as the number of participants meeting the endpoint definition, but the count alone does not show the underlying risk unless its denominator and completeness of follow-up are also clear.

The registry specifies a 100-day timeframe, which gives the endpoint a defined observation window. It does not report additional detail on how causes of death were adjudicated, how deaths with uncertain or multiple causes were classified, or how participants without complete follow-up were handled. These details are relevant because the endpoint depends on both the timing of death and its attribution as unrelated to relapse.

The posted results available in the registry record do not include a numerical primary-endpoint result or an uncertainty interval. Accordingly, the endpoint definition can be described, but its observed frequency and precision cannot be assessed from the reported information.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

Statistical interpretation begins with the design and the type of outcome being reported. This study is described as non-randomized and single-group. General statistical principle: random allocation can help balance measured and unmeasured factors between groups, while non-randomized groups may differ in ways that affect outcomes. As a result, comparisons across the AUC levels are descriptive unless a suitable analysis and supporting assumptions are reported. No such adjusted comparison is described in the registry record.

What does an AUC target represent?

AUC means area under the plasma concentration-time curve. In general, it summarizes drug exposure over time, rather than representing a single concentration measurement. The registry states that daily busulfan doses were adjusted using blood samples to target an AUC level. It lists target levels of 6000 +/- 600 uM-min, 7500 +/- 750 uM-min, and 9000 +/- 900 uM-min. The available record does not give participant-level measured AUC values, the extent to which targets were achieved, or variability in achieved exposure.

The use of exposure-based dosing is relevant to interpreting the intervention: the study concerns dose escalation guided by measured drug exposure, not simply assignment to fixed doses. The record does not report the actual dose adjustments for individual participants or whether any participants did not reach their target. Those details limit assessment of how closely the treatment received corresponded to the intended exposure levels.

How should the primary endpoint be read?

The primary outcome is a binary event summarized as a count: whether a participant died from a cause unrelated to relapse within the 100-day timeframe. General statistical principle: a count is easier to interpret when accompanied by the number of participants at risk, a clearly defined analysis population, and an uncertainty interval. The registry specifies intent to treat as the population, but does not report the observed primary count or an interval estimate. Thus neither the observed frequency nor its statistical precision can be assessed.

A confidence interval, in general, describes uncertainty around an estimate under the assumptions of the analysis. It is not a guarantee that the true value lies within the interval. No confidence interval for non-relapse mortality is reported in the registry record. A p-value, if one were reported, would address compatibility with a specified null model; it would not by itself establish clinical importance or remove limitations from non-randomized allocation. No primary-endpoint p-value is reported.

Why do unequal groups matter?

The serious adverse event counts are presented for groups with different numbers at risk. General statistical principle: estimates based on smaller groups are generally less precise than estimates based on larger groups, all else equal. The AUC Level 3 group has 3 participants at risk in the registry record, so its observed count has little capacity to characterize the range of outcomes that might occur in a broader population. The record does not provide confidence intervals or a model that would quantify this uncertainty.

Over-dispersion is a general concern when event counts vary more than a simple statistical model expects. It can make standard errors too small if a model assumes less variability than the data contain. This is a general concept, not a claim that over-dispersion was measured or that a particular count model was used in this study. The registry record does not report a model for the serious adverse event counts.

What can planning calculations say?

General statistical principle: sample-size planning asks how many participants would be needed to detect an assumed effect under specified assumptions. It is not a summary of what happened in a completed trial. The stated planning illustration uses a two-sided significance level of 0.05, equal allocation, and a normal approximation, with the effect framed as a fraction of the observed effect. Such an illustration depends on its assumptions, including the effect used as a planning target. It does not establish that the original study was designed with those assumptions, and it is not observed power.

The registry record does not report a sample-size justification for the study, nor does it report an original statistical analysis plan or a power calculation. The planning illustration should therefore be distinguished from the trial's design rationale. No new estimate or sample size can be inferred from the reported information without additional inputs.

How should adverse-event percentages be handled?

The registry lists serious adverse event terms with percentages. General statistical principle: a percentage is interpretable only when its denominator and event-counting rules are clear. The available record does not specify the denominator for the listed term percentages, nor whether participants could contribute to more than one term. It would therefore be inappropriate to infer the number of events, add percentages together, or treat the terms as mutually exclusive. The percentages should be quoted as registered, with this denominator uncertainty kept in view.

Overall, the methods information supports a descriptive reading of the dose levels, the listed event counts, and the stated endpoint definition. It does not support a causal dose comparison or a precision claim for the primary outcome. Details of covariate adjustment, missing-data handling, endpoint adjudication, and formal analysis methods are not reported in the registry record.

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("AUC 6000", "AUC 7500", "AUC 9000")
n      <- c(40, 29, 3)
events <- c(3, 4, 2)
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  AUC 6000  40  3  7.5  1.6  20.4  2.6  19.9  2.7  19.9
ARM  AUC 7500  29  4  13.8  3.9  31.7  5.5  30.6  5.6  30.7
ARM  AUC 9000  3  2  66.7  9.4  99.2  20.8  93.9  19.4  93.2

11. Multiplicity, Missing Data and Analysis Populations

The registry lists two outcome measures and two analyses, identifies non-relapse mortality as the primary outcome, and lists severe venous occlusive disease/sinusoidal obstructive syndrome as a secondary outcome. It does not report the complete analysis plan or explain how multiple outcomes, dose levels, or statistical tests were handled. A multiplicity adjustment or testing hierarchy is not reported in the registry record.

General statistical principle: when many outcomes or comparisons are examined, the chance of obtaining an apparently unusual result by chance can increase. Prespecifying a primary outcome and analysis can help clarify interpretation, but the record does not provide enough detail to determine the full set of planned comparisons or whether they were prespecified. No p-values for the primary endpoint or secondary outcome are reported in the information available for this analysis.

The record identifies the primary endpoint population as intent to treat. It does not report how missing outcome information, loss to follow-up, withdrawal, or incomplete ascertainment was handled. The number of participants with complete primary-endpoint follow-up is not reported in the registry record. Nor does the record explain whether participants were analyzed according to intended dose level, received exposure, or another grouping rule.

These omissions do not establish that data were missing or that analyses were conducted in a particular way. They mean that completeness and analysis choices cannot be evaluated from the registry record. The stated population label alone does not describe how missing observations or deviations from the intended regimen were treated. As a result, interpretation should remain limited to the definitions and descriptive figures that are actually reported.

12. 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

Serious events with the highest arm-level rate: hemorrhage, gi - stomach (33.3%), liver dysfunction/failure (clinical) (33.3%), infection with normal anc or grade 1 or 2 neutrophils - lung (pneumonia) (10.3%), cardiac ischemia/infarction (3.4%), nausea (3.4%).

The serious adverse event figures are grouped by busulfan AUC level. The record reports 2 affected participants among 40 at AUC Level 1, 13 among 29 at AUC Level 2, and 2 among 3 at AUC Level 3. It also reports 0 other affected participants in each of those groups. These are registry counts and denominators, not a randomized comparison or an adjusted estimate of treatment effect.

The listed serious adverse event terms include gastrointestinal stomach hemorrhage and clinical liver dysfunction or failure, each at 33.3%; lung infection with normal ANC or Grade 1 or 2 neutrophils (pneumonia) at 10.3%; and cardiac ischemia or infarction, nausea, and Death NOS, each at 3.4%. The registry record does not specify the denominator for these term percentages in the information. They should not be read as percentages of all enrolled participants or as mutually exclusive categories without that clarification.

Group sizes differ, and the AUC Level 3 group includes 3 participants at risk. Counts from such a small group describe only the recorded experience in that group; they do not precisely characterize how often events would occur in a larger population. The record does not report event attribution, follow-up duration for these serious adverse events, or uncertainty intervals. These figures describe what the registry lists and should not be used to infer causation or compare safety across levels as if assignment were randomized.

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

The registry record documents a dose-escalation study of busulfan exposure with fludarabine before allogeneic hematopoietic cell transplantation. It describes the AUC targets, the primary endpoint definition, and serious adverse event counts by dose level. It does not report the primary non-relapse mortality result, and the listed secondary outcome of severe VOD/SOS has no result reported in the information available for this analysis.

Consequently, the posted record does not establish the observed frequency of non-relapse mortality within 100 days. It also does not provide an uncertainty interval for that endpoint. A missing result should not be interpreted as zero events, as a favorable outcome, or as proof that the endpoint was not assessed. It indicates that the result is not reported in the registry record.

The serious adverse event counts show that affected participants were recorded at each AUC level, with different group sizes. Because the study was non-randomized and had no control group, those counts cannot isolate a causal effect of busulfan exposure. They do not show what would have happened to comparable participants under a different regimen or dose. Differences between levels could reflect factors that the record does not describe.

The record's description of exposure-guided dose adjustment is informative about the study's intervention, but actual measured AUC values and target attainment are not reported. The maximally tolerated level or AUC is stated as a study objective; the available results do not establish which level met that objective. Nor do the posted details show whether higher exposure produced a therapeutic benefit.

The appropriate interpretation is therefore descriptive and limited. The registry records a completed, Phase 4 study with enrollment of 72 and presents some serious adverse event counts, but the information available does not support a primary-outcome conclusion, a causal dose comparison, or a definitive estimate of safety or benefit.

14. Why This Trial Matters Statistically

This study raises statistical issues that commonly arise in dose-escalation research. Exposure-guided dosing makes the intervention more complex than assignment to a fixed dose: participants' doses were adjusted using blood concentration measurements, and the intended comparison concerns AUC targets. Without reported measured exposure and target attainment, it is difficult to connect the assigned level to the exposure actually achieved.

The non-randomized, single-group structure also shapes what can be learned. Dose escalation can describe outcomes observed at successive exposure levels and can support a dose-finding objective when its rules and outcomes are fully reported. However, the level groups do not automatically provide a fair treatment comparison. A statistical analysis cannot remove the design limitation unless the relevant factors are measured, modeled appropriately, and supported by adequate data; those methods are not described in the registry record.

The record also illustrates why endpoint results and uncertainty matter. Non-relapse mortality is clearly defined by cause and timeframe, but its observed count is not reported. Without that result, readers cannot judge the primary outcome's magnitude or precision. Serious adverse event counts are reported, but denominators vary and one group is very small. Descriptive counts are valuable, yet they do not provide the same information as estimates with uncertainty or comparisons designed to address confounding.

Finally, separating planning calculations from observed evidence is important. A sample-size illustration built from an observed effect can help readers consider hypothetical planning assumptions, but it is not the trial's original design justification and does not establish observed power. This distinction helps prevent a planning exercise from being mistaken for an outcome or a guarantee that the study could answer its primary question.

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 consequential limitation of the available registry information is that the numerical result for the primary endpoint, non-relapse mortality within 100 days, is not reported. The record also does not report an uncertainty interval for that endpoint. As a result, the main outcome cannot be quantitatively interpreted from the available results.

The design was non-randomized and single-group, with no like-for-like control comparison. Any apparent pattern across AUC levels is descriptive and could reflect differences between participants or other factors, not only exposure. The registry does not report participant characteristics by level, the rules for dose escalation, or the reasons the serious adverse event group sizes differ.

For the serious adverse event figures, the record supplies counts and denominators by level, but no uncertainty estimates or adjusted analyses. The AUC Level 3 group includes 3 participants at risk. The term percentages are listed without a denominator in the information, and the record does not explain whether a participant could contribute to multiple terms. Event attribution and follow-up details are also not reported.

The registry identifies intent to treat for the primary outcome, but does not describe missing-data handling, the number with complete follow-up, or the treatment of deviations from the intended regimen. The measured AUC values and success in reaching targets are not reported. A formal statistical plan, a sample-size justification, multiplicity handling, and the endpoint result for severe VOD/SOS are also not reported in the registry record. These gaps constrain assessment of both the results and their precision.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Busulfan Safety/Efficacy as Conditioning Prior to Hematopoietic Cell Transplantation (HCT) — NCT00361140.
• Registry record last updated 2017-03-03; status last verified 2013-06.
• Results first posted 2013-06-27.
• 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

NCT00361140 is a completed Phase 4, non-randomized, single-group study of AUC-guided busulfan with fludarabine before allogeneic hematopoietic cell transplantation. The registry lists enrollment of 72, a start date of 2005-08, and primary completion in 2012-02. The dose-escalation objective was to determine a maximally tolerated busulfan level or AUC and evaluate the potential therapeutic benefit of higher doses.

The primary endpoint was the number of intent-to-treat participants who died from causes unrelated to relapse within 100 days after transplant. Its result is not reported in the registry record. Serious adverse event counts are reported for the three AUC levels, but the non-randomized design and unequal group sizes do not support a causal comparison. The listed secondary outcome, severe VOD/SOS, has no result reported in the information available for this analysis.