Combination 5-azacitidine and Gemtuzumab Ozogamicin Therapy for Treatment of Relapsed Acute Myeloid Leukemia (AML): Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Combination 5-azacitidine and Gemtuzumab Ozogamicin Therapy for Treatment of Relapsed Acute Myeloid Leukemia (AML) (NCT00766116), a non-randomized phase 1, phase 2 study. The primary outcome is Number of Participants With Dose Limiting Toxicities.

2. Clinical Question

3. Trial Design

This was a Phase I/II study of 5-azacitidine combined with gemtuzumab ozogamicin in relapsed acute myeloid leukemia. The registry describes the design as non-randomized, unmasked, and sequential. Those features matter: participants were not assigned at random to a treatment or control group, and the record does not establish a concurrent comparison capable of separating treatment effects from other differences between groups or changes over time.

The Phase I portion assessed three dose levels. The first used 5-azacitidine for 2 days followed by gemtuzumab ozogamicin at 3 mg/m². The second used 5-azacitidine for 4 days followed by gemtuzumab ozogamicin at 6 mg/m². The third used 5-azacitidine for 6 days followed by gemtuzumab ozogamicin at 6 mg/m². The registry description reports cohorts of 6, 4, and 4 patients, respectively, and says no dose-limiting toxicities were identified. It identifies the Phase II dose as 5-azacitidine for 6 days.

The registry lists enrollment of 50 and marks the study completed. Its recorded start is 2005-07, and primary completion is dated 2014-09-26. These dates describe the registry record; they do not supply further details about accrual, follow-up, or the timing of analyses. The statistical analysis plan, including any planned comparisons or interim analyses, is 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.

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.

6. Primary Endpoint

The registry lists the primary outcome as Number of Participants With Dose Limiting Toxicities, measured over up to 28 days.

The primary endpoint is the number of participants with dose-limiting toxicities. The registry gives a timeframe of up to 28 days and describes assessment during cycle 1 of therapy using CTCAE Version 3.0. In the Phase I portion, the endpoint was used to guide dose selection: the maximum tolerated dose was defined as the maximum number of 5-azacitidine doses at which fewer than 1/3 of patients experienced a dose-limiting toxicity.

In general, toxicity-based dose selection is used in early-phase research to identify a dose level that can be carried forward for further study. A count of participants with at least one qualifying toxicity is different from a count of all toxicity episodes: it treats each participant as the unit of analysis for this endpoint. It also differs from a measure of overall safety, since the endpoint focuses on toxicity meeting the specified dose-limiting criteria within the stated timeframe.

The registry description reports no dose-limiting toxicities in the Phase I cohorts and identifies the Phase II dose as 5-azacitidine for 6 days. A complete endpoint result for all enrolled participants, including the number assessed and the detailed criteria for each toxicity, is not reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does a participant count represent?

The primary endpoint is a count of participants with dose-limiting toxicities, rather than a count of every toxicity episode. As a general statistical principle, participant counts are useful when the question is how many people experienced at least one qualifying event. They do not describe how many events each person experienced, how long events lasted, or whether events recurred. Those details are not reported in the registry record.

The registry describes a threshold for dose selection: fewer than 1/3 of patients experiencing a dose-limiting toxicity during cycle 1. This is a decision rule for identifying a dose level in the Phase I portion, not a comparison of the combination against another treatment. The narrative reports no dose-limiting toxicities in the Phase I cohorts and identifies the Phase II dose as 5-azacitidine for 6 days. A separate complete count for the primary endpoint across all participants is not reported.

Why does the design affect interpretation?

In general, randomization helps balance measured and unmeasured participant characteristics across treatment groups. This trial is recorded as non-randomized and sequential, so that protection is not available. A sequential dose-finding design evaluates dose levels in an order rather than assigning participants randomly among a treatment and control. Descriptive outcomes can be reported, but the design does not by itself support a causal comparison between the combination and an alternative.

The registry also records no masking. In general, masking can reduce the influence of knowledge of treatment assignment on outcome assessment or reporting. The record does not describe procedures to mitigate that possibility, nor does it report how dose-limiting toxicities were adjudicated.

What does uncertainty mean?

In general, a confidence interval expresses the range of values compatible with the data under a specified statistical method. It conveys the precision of an estimate; a point estimate alone does not show how uncertain that estimate is. The registry record does not report confidence intervals or other uncertainty estimates for the primary endpoint or the safety summaries. The small Phase I cohorts described in the record also mean that the absence of an observed dose-limiting toxicity in those cohorts does not establish that such events cannot occur.

The registry gives CTCAE Version 3.0 as the basis for assessing dose-limiting toxicity, but does not provide the detailed event criteria or the analysis population used for the endpoint. A clear definition and denominator are important for interpreting a participant count. Without a full account of who was assessed, how missing assessments were handled, and how events were classified, the completeness of the result cannot be evaluated from the registry record.

How should the planning illustrations be understood?

In general, a sample-size calculation estimates the amount of information a future study might need to detect a chosen effect under stated assumptions. The planning illustrations associated with this trial are described as using a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. They use a fraction of the observed effect as the effect to detect. These are planning assumptions, not evidence that the trial itself used those design choices.

The registry describes this study as non-randomized, sequential, and dose-finding. A hypothetical equal-allocation comparison between two arms therefore should not be read as the actual trial design. In general, planning sample sizes are not observed power: they do not measure the probability that the completed trial detected an effect, and they do not replace reported outcome estimates and uncertainty intervals. The registry record does not report its own statistical plan or a sample-size justification.

What is not available for statistical evaluation?

The registry record does not report an inferential analysis, adjusted estimates, a model specification, or a formal comparison between groups. It also does not report analysis populations, missing-data methods, or a detailed account of participant flow. As a result, the posted information supports descriptive interpretation of the stated dose-finding and safety results, but not reanalysis of the primary endpoint or a formal assessment of treatment effects.

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("Phase 1 Cohort 1", "Phase 1 Cohort 2", "Phase 1 Cohort 3")
n      <- c(6, 4, 4)
events <- c(0, 0, 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  Phase 1 Cohort 1  6  0  0.0  0.0  45.9  0.0  39.0  0.4  41.0
ARM  Phase 1 Cohort 2  4  0  0.0  0.0  60.2  0.0  49.0  0.5  52.2
ARM  Phase 1 Cohort 3  4  0  0.0  0.0  60.2  0.0  49.0  0.5  52.2

11. Multiplicity, Missing Data and Analysis Populations

The registry lists a primary endpoint of participants with dose-limiting toxicities and a secondary outcome of participants with response to the combination. It does not report a statistical analysis plan specifying how these outcomes were to be tested, whether there were additional planned outcomes, or how any multiplicity was to be addressed. In general, testing multiple outcomes can increase the chance of a nominally unusual result, so the planned hierarchy and interpretation of tests matter. No such testing strategy is reported in the registry record.

The record does not report inferential analyses, p-values, confidence intervals, or adjusted estimates. It therefore does not allow assessment of whether any reported analysis accounted for multiple outcomes, dose levels, or repeated looks at accumulating data. The record also does not report whether interim analyses were planned or conducted; no assumption about them is warranted.

Information about missing data and analysis populations is also not reported in the registry record. It does not specify how many participants were evaluable for each outcome, how missing toxicity assessments or response assessments were handled, or whether all enrolled participants were included in each analysis. In general, missingness can affect both the denominator and the interpretation of an event rate, especially if availability of an assessment is related to a participant’s outcome.

The enrollment entry and the safety denominators do not, by themselves, establish that every participant contributed to every endpoint. The registry’s Phase I narrative reports cohort sizes and a dose-finding conclusion, but does not give a full accounting of exclusions, withdrawals, or endpoint-specific evaluability. These omissions limit reproduction of the analysis and evaluation of potential bias.

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 0% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: neutropenic fever (22.0%), pneumonia (4.0%), sepsis (4.0%), abdominal pain (2.0%), cardiopulmonary arrest (2.0%).

The registry safety summary lists 20 participants with serious adverse events and 44 with other adverse events, with 50 at risk in each category. Serious adverse event terms include neutropenic fever at 22.0%, pneumonia at 4.0%, sepsis at 4.0%, abdominal pain at 2.0%, cardiopulmonary arrest at 2.0%, and fever at 2.0%.

These figures are descriptive safety information. The record does not state whether the listed terms were judged related to study treatment, whether an individual could contribute more than one term, or how the terms were selected for display. It also does not provide timing, duration, severity grades, or event-level counts for each listed term. The percentages should therefore be read as registry-reported summaries, not as a complete account of the number or course of adverse events.

In general, a serious adverse event is a safety classification distinct from a dose-limiting toxicity. The primary endpoint’s dose-limiting criteria and timeframe are not interchangeable with the broader serious adverse event summary. Because the design is non-randomized and the record does not report a control group, these safety figures cannot establish comparative risk or attribute events to the combination.

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

The registry record documents a Phase I/II investigation of 5-azacitidine with gemtuzumab ozogamicin in relapsed acute myeloid leukemia. Its primary endpoint was a participant count for dose-limiting toxicities, used in Phase I dose selection. The narrative reports no dose-limiting toxicities in the Phase I cohorts and identifies a Phase II dose of 5-azacitidine for 6 days.

That dose-finding result is not the same as evidence that the combination improves disease outcomes. The registry lists response as a secondary outcome, but a response result is not reported in the registry record. Nor does the record report a randomized comparison, an alternative-treatment group, or inferential estimates of a treatment effect. The trial’s non-randomized, sequential design does not provide a like-for-like control comparison.

The safety summary reports participants with serious and other adverse events and lists several serious adverse event terms. These descriptive reports do not establish that the study drugs caused the events, and they cannot quantify how safety compares with another treatment. The registry does not report event attribution or the detail needed to reconstruct the safety experience.

In general, conclusions about an intervention depend on the outcome measured, the completeness of outcome ascertainment, the comparison design, and the precision of estimates. Here, the available record is most informative about the stated Phase I dose-finding result and the existence of recorded safety events. It does not provide a response estimate, a comparative effect, or uncertainty intervals. The absence of a reported result should not be interpreted as a result of zero effect or zero events; it means the result is not reported in the registry record.

14. Why This Trial Matters Statistically

This trial illustrates the distinct role of early-phase dose-finding and later evaluation of clinical outcomes. The primary endpoint was a toxicity count used to guide dose selection, with the Phase I narrative reporting no dose-limiting toxicities in the cohorts and identifying a Phase II dose. That addresses a dose-selection question; it does not answer whether the combination improves outcomes compared with another treatment.

The registry’s non-randomized, sequential design is statistically important. Without random assignment and a like-for-like control group, observed outcomes cannot be interpreted as a comparative treatment effect. This distinction is especially important when a registry includes a secondary response outcome but does not report its result: the presence of an outcome name is not evidence of an observed response estimate.

The record also highlights why denominators, outcome definitions, and uncertainty estimates matter. Counts of participants with events are easier to interpret when the analysis population and assessment completeness are clear. Here, the registry does not report full endpoint-specific evaluability, missing-data handling, or confidence intervals. Those omissions constrain how precisely the dose-finding and safety summaries can be understood.

Finally, planning calculations should be separated from the design and findings of the completed trial. General assumptions used for a planning illustration do not establish the study’s own statistical plan, and they are not observed power. The trial record is a useful case for distinguishing a descriptive early-phase safety result from comparative evidence and for recognizing the information needed to evaluate each.

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 registry record does not report a complete primary endpoint result for all participants, endpoint-specific denominators, or the number assessed at each dose. It gives Phase I cohort sizes and a narrative statement about dose-limiting toxicities, but not a participant flow account or detailed descriptions of toxicity cases. This makes it difficult to verify the endpoint’s completeness or independently reproduce its analysis.

The dose-finding design was non-randomized and sequential, with no masking. The record does not report a control group or a like-for-like comparison. Accordingly, the results cannot isolate effects of the combination from other influences, and differences across dose levels should not be interpreted as randomized comparisons.

The registry does not report a response result, inferential analyses, confidence intervals, p-values, or a statistical analysis plan. Details about multiplicity, missing data, analysis populations, interim analyses, and sample-size justification are also not reported in the registry record. These absences prevent assessment of the precision of outcome estimates and of whether analyses followed prespecified methods.

The safety summary lacks event-level information, treatment attribution, timing, and severity details for the listed terms. Its counts and percentages should therefore be treated as descriptive registry summaries rather than a comprehensive comparative safety analysis. The record’s stated completion status does not resolve these reporting limitations.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Combination 5-azacitidine and Gemtuzumab Ozogamicin Therapy for Treatment of Relapsed Acute Myeloid Leukemia (AML) — NCT00766116.
• Registry record last updated 2019-02-18; status last verified 2019-01.
• Results first posted 2019-02-18.
• 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

NCT00766116 is a completed, non-randomized Phase I/II study of 5-azacitidine with gemtuzumab ozogamicin for relapsed acute myeloid leukemia. It was unmasked and sequential, with enrollment listed as 50.

The primary endpoint was the number of participants with dose-limiting toxicities over up to 28 days. The Phase I description reports no dose-limiting toxicities in its cohorts and identifies 5-azacitidine for 6 days as the Phase II dose. Response was listed as a secondary outcome, but its result is not reported in the registry record.

The safety record reports 20 participants with serious adverse events and 44 with other adverse events, with 50 at risk in each category. The registry does not report a control comparison, inferential analysis, confidence intervals, analysis populations, or missing-data methods. Interpretation is therefore limited to the descriptive dose-finding and safety information recorded.