Obatoclax for Systemic Mastocytosis: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Obatoclax for Systemic Mastocytosis (NCT00918931), a non-randomized phase 2 study. The primary outcome is Response Rate.

2. Clinical Question

The study’s stated purpose was to learn whether obatoclax mesylate could help control systemic mastocytosis and to test its safety. Those are the aims recorded, not findings. Because the study enrolled 3 participants and has no reported primary analysis, the record does not establish how often objective response occurred in the evaluated participants. It also does not show whether any observed changes could be attributed to the intervention rather than other influences. The study is best read as a small, single-group investigation with a defined response question, rather than as a comparison of treatments.

3. Trial Design

This was a phase 2, non-randomized, single-group study with no masking. The registry lists enrollment of 3 participants. All participants were assigned to the obatoclax mesylate intervention; no separate control arm is described. Accordingly, there is no randomized comparison, and the design does not support a direct estimate of the difference between obatoclax and another treatment or no treatment.

The listed schedule was 30 mg by vein over 3 hours on Days 1-3 of a 14-day cycle. The registry record does not report the planned treatment duration, the number of cycles intended, or how many cycles each participant received. It also does not report further details of allocation beyond identifying the study as non-randomized, or explain why the study was stopped.

The study started in 2009-06, had a primary completion date of 2010-10, and is marked terminated. These entries describe the record’s status and timeline; they do not explain whether the study ended early, whether all planned procedures were completed, or why termination occurred. The reason for termination is not reported in the registry record.

The registry identifies one primary outcome measure, Response Rate, with a 3-Month Response Evaluation timeframe. The analysis population is described as per protocol. Although the record includes the outcome definition, it lists no analyses. It therefore does not report the response numerator or denominator, an estimate of the response rate, or inferential results. The record also does not provide a sample-size justification or a statistical analysis plan.

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: Three patients were registered and all of them received treatment.

Overall Study

Analysis population for the primary outcome, as defined in the registry: Analysis was per protocol.

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 Response Rate, measured over 3-Month Response Evaluation.

The primary endpoint was Response Rate at the 3-Month Response Evaluation. It is defined as the number of participants with an objective response divided by the number of participants evaluated. Objective response includes complete response and partial response under the definitions recorded for this study. A complete response constitutes total elimination of a symptom or sign of disease; a partial response constitutes at least 50% improvement in a symptom or sign. The definitions were based on guidelines proposed by Valent et al. and described as International working group consensus criteria.

A response-rate endpoint condenses a clinical assessment into a count of participants meeting a specified response definition relative to the evaluated group. In general, a prespecified definition helps make the classification interpretable and consistent, while a stated assessment time identifies when the response is to be judged. The endpoint is not a measure of how long a response lasts, and the registry does not define it as a time-to-event outcome.

The registry says analysis was per protocol, but does not provide the number who met that analysis population definition or the number evaluated at the response assessment. It also does not report how participants with missing assessments were handled. Most importantly, no response count or rate is posted in the registry record. The endpoint’s definition is available; its observed result is not.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry identifies the primary outcome as a binary response measure expressed in participants: each evaluated participant either meets the objective-response definition or does not. The outcome’s stated rate uses the number with response divided by the number evaluated. This is the endpoint definition, not a reported result. Neither component count nor a resulting estimate appears in the registry record.

What does a response-rate estimate represent?

In general, a response-rate estimate is a summary of the observed proportion of participants classified as responders in a defined analysis group. Its meaning depends on consistent application of the response criteria, a clear assessment time, and a clear denominator. The registry specifies response criteria and a 3-Month Response Evaluation, and says the primary analysis was per protocol. It does not report the evaluated denominator, the per-protocol count, or the number meeting the criteria. As a result, the endpoint cannot be reconstructed from the posted record.

How should uncertainty be interpreted?

In general, a confidence interval accompanies an estimate to represent statistical uncertainty under an assumed model. For a binary response endpoint, the interval depends on the observed response count and the number evaluated. A small amount of information generally makes an estimate less precise, but no interval can be characterized because the response estimate and evaluated denominator are not reported. No confidence interval, standard error, p-value, or hypothesis-test result is listed for the primary outcome. It would be inappropriate to infer any of these from enrollment alone.

General statistical interpretation also distinguishes observed data from a claim about a broader population. An observed response frequency, if reported, would describe the analyzed participants; generalizing beyond them requires attention to eligibility, study conduct, and uncertainty. In this record, there is no posted response frequency to interpret, and details needed to assess representativeness are not reported.

What does the design allow?

The study is identified as non-randomized and single group, with no masking. In general, random allocation can help make groups comparable at baseline, while a concurrent control can provide a reference for changes that might occur without the intervention. This design has no such comparator. Consequently, it cannot estimate a randomized between-group contrast. Even if a response count were available, interpreting it as an effect caused by treatment would require caution because the record does not provide a control-group outcome.

Masking can, in general, reduce the potential for knowledge of treatment assignment to influence assessments or other study procedures. The record states that there was no masking. It does not report whether the response assessment involved additional safeguards or independent review. That information is not reported in the registry record.

What can the safety counts tell us?

Safety counts describe how many participants were recorded as affected within the relevant group and how many were at risk. The registry lists 3 at risk and 0 affected for serious adverse events, and 3 at risk and 3 affected in the other adverse-event grouping. These are counts, not comparative estimates. General interpretation of adverse-event data depends on event definitions, observation time, ascertainment, severity, and participant exposure. The registry does not report detailed terms for the other events, time at risk, or further information on ascertainment. It also does not provide a comparator arm for a relative safety contrast.

The serious-event count of 0 is a record of no affected participants in that group as posted; it should not be converted into a claim that serious events are impossible or that the intervention is free of serious risk. The record’s deaths field is not reported, so it does not establish a death count.

What statistical planning is reported?

The registry record does not report the trial’s own sample-size justification, statistical analysis plan, or interim analyses. A planning illustration described in the record uses a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation, with the effect to detect stated as a fraction of the observed effect. Those are planning assumptions for an illustration, not evidence that the trial used a two-arm design: the actual study is recorded as single group and non-randomized. No numerical planning result is reported in the entry, and such illustrations are not observed power or a substitute for the missing outcome analysis.

General statistical practice also distinguishes a planned analysis from an analysis of the collected data. The record lists zero analyses, so it does not document the primary outcome’s computed estimate or an inferential analysis. Any further statistical procedures, including adjustment, model choice, or handling of repeated measurements, 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("Obatoclax Mesylate")
n      <- c(3)
events <- c(0)
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  Obatoclax Mesylate  3  0  0.0  0.0  70.8  0.0  56.1  0.6  60.2

11. Multiplicity, Missing Data and Analysis Populations

The registry lists one outcome measure, identified as the primary Response Rate at the 3-Month Response Evaluation, and lists zero analyses. It does not report a multiplicity adjustment or a strategy for interpreting results across multiple outcomes or analysis choices. With no analysis results posted, there is no reported set of endpoint tests from which to assess multiplicity in practice. The presence of one listed outcome measure does not establish that no additional analyses were planned or conducted; that information is not reported in the registry record.

The primary population is described as per protocol. The record does not define the per-protocol criteria, state how many participants met them, or explain how participants were handled if they did not complete treatment or the response assessment. The number evaluated for the primary outcome is not reported. A response-rate denominator therefore cannot be confirmed from the enrollment figure alone.

Missing-data methods are not reported in the registry record. The entry does not explain whether missing response assessments were excluded, counted as non-response, imputed, or handled in another way. It also does not say whether any participants discontinued or were lost to follow-up. Those details matter because the analyzed group and missing-outcome handling can affect the interpretation of a response-rate endpoint.

The registry does not report an intention-to-treat analysis, a sensitivity analysis, or a comparison between analysis populations. No statistical analysis plan or interim analysis details are reported. These absences limit assessment of how the analysis was selected and how robust a result would be, but they should not be interpreted as proof that a particular method was or was not used outside what the registry records.

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 non-serious adverse event terms

The safety summary lists the obatoclax mesylate group with 3 participants at risk for serious adverse events and 0 affected. It separately lists 3 participants at risk and 3 affected in the other adverse-event grouping. These are participant counts in the registry record. The other-event terms are not listed, and the record gives no further description of their nature, severity, timing, or duration. No serious adverse-event terms are listed.

The count of 0 affected for serious adverse events should be understood as the posted count, not as proof that serious adverse events cannot occur. The record does not state the observation period used for these counts or provide detailed event-collection methods. It also has no comparison group, so the counts do not quantify a relative difference in safety between treatments.

Deaths are not reported in the registry record. A missing death count should not be read as a count of zero. More generally, these limited figures do not describe every possible safety outcome or establish a complete safety profile. They report the listed counts for the group and event categories recorded.

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

The registry record establishes that a phase 2, non-randomized, single-group study evaluated obatoclax mesylate in patients with systemic mastocytosis, with a primary response-rate endpoint assessed at 3 months. It also records the response definition, the per-protocol analysis population, the intervention schedule, enrollment of 3, and limited adverse-event counts. These registry entries describe the study’s intended question and the information posted about its design and safety summary.

The record does not report the number of participants with an objective response, the number evaluated, or a response-rate estimate. It therefore does not show the observed frequency of response or how precisely that frequency was estimated. It also does not report a primary statistical analysis, a confidence interval, or a p-value. No conclusion about the primary endpoint’s result can be drawn from this entry.

Because there was no comparator group and no randomization, the study design does not provide a direct comparison of obatoclax with another intervention. The absence of a comparator does not make the study question meaningless; it means the record cannot establish a between-group treatment contrast. A single-group observation also does not, by itself, distinguish an intervention-associated change from other influences.

The safety summary records 0 participants affected by serious adverse events among 3 at risk and 3 affected in the other adverse-event grouping among 3 at risk. The other event terms and death count are not reported. These counts should be interpreted only as the posted safety figures, not as proof of safety or a comprehensive assessment of risk.

Finally, the study is marked terminated, but the reason is not reported in the registry record. The entry does not establish why it ended or whether planned procedures were completed. Taken together, the record documents a narrowly defined research question and study design, while leaving the primary response result, its uncertainty, and important analysis details unreported.

14. Why This Trial Matters Statistically

This study illustrates how a registry entry can define an outcome clearly without reporting its observed result. The response endpoint has a stated timepoint and explicit criteria for complete and partial response, which are important elements for understanding what the investigators intended to measure. Yet the registry does not list the response count, evaluated denominator, or any analysis. Statistical interpretation depends on those observed data as well as the endpoint definition.

It also illustrates the distinction between describing an intervention and estimating a treatment effect. A single-group, non-randomized design can record outcomes among participants who received an intervention, but without a control group it does not directly estimate how those outcomes compare with an alternative. The lack of masking is another design feature relevant to how assessments may be interpreted, although the registry does not describe the assessment procedures in further detail.

The small enrollment of 3 makes careful attention to denominators and uncertainty especially important. Enrollment is not necessarily the same as the number evaluated for the primary endpoint, and the registry does not state how many participants entered the per-protocol analysis. Without those details, even a basic response-rate summary cannot be verified from the posted record.

Finally, safety counts require context. The posted serious-event and other-event counts are not accompanied by event terms, observation time, or a comparison group. This example underscores why counts should be reported alongside clear definitions and relevant denominators, and why missing results should remain distinct from evidence of no effect or no risk.

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.

Several limitations specific to this record constrain interpretation. Enrollment was 3, and the registry does not report how many participants were evaluated for the primary endpoint or included in the per-protocol analysis. Since Response Rate is defined using the number evaluated as its denominator, the missing denominator prevents calculation or verification of the endpoint from the registry entry.

The study was single group, non-randomized, and unmasked. There was no like-for-like control comparison, so the design cannot provide a randomized contrast with another treatment. The registry does not report additional assessment safeguards that might clarify how response was determined in the absence of masking.

The study is marked terminated, but the reason for termination is not reported in the registry record. The record also does not clarify whether the planned study activities were completed, how many treatment cycles participants received, or whether any response assessments were missed. Missing-data procedures, per-protocol criteria, and analysis-population counts are not reported.

No primary outcome results or statistical analyses are posted. The registry does not report a response estimate, confidence interval, p-value, sample-size justification, statistical analysis plan, interim analyses, or multiplicity approach. The serious-event summary has no affected participants listed among 3 at risk, while 3 participants are listed as affected in the other adverse-event grouping. The other event terms, the observation period, and the deaths count are not reported. These gaps prevent a detailed assessment of either efficacy or safety from the registry record alone.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Obatoclax for Systemic Mastocytosis — NCT00918931.
• Registry record last updated 2011-11-04; status last verified 2011-10.
• Results first posted 2011-04-25.
• 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 NCT00918931, Obatoclax for Systemic Mastocytosis, as a phase 2, non-randomized, unmasked, single-group study sponsored by M.D. Anderson Cancer Center. Enrollment was 3. The study started in 2009-06, had primary completion in 2010-10, and is marked terminated.

Participants received obatoclax mesylate by vein at 30 mg over 3 hours on Days 1-3 of a 14-day cycle. The primary outcome was Response Rate at the 3-Month Response Evaluation, defined using complete and partial response criteria. The primary population was per protocol. The registry lists one outcome measure and zero analyses; it does not report the response count, evaluated denominator, or response-rate result.

The safety summary lists 0 affected by serious adverse events among 3 at risk, and 3 affected in the other adverse-event grouping among 3 at risk. Event terms for the other grouping and deaths are not reported in the registry record. The reason for termination, analysis plan, and sample-size justification are also not reported.