Anti-tumor Effect of Ixabepilone in Metastatic Breast Cancer (mBC) Selected by the Ixabepilone DRP.: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Anti-tumor Effect of Ixabepilone in Metastatic Breast Cancer (mBC) Selected by the Ixabepilone DRP. (NCT04796324), a na phase 2 study. The primary outcome is Clinical Benefit Rate (CBR).

2. Clinical Question

This is a single-group study, not a randomized comparison. Its stated clinical question concerns a selected population: eligibility involved prior failure of anthracycline and taxane treatment, and selection by the Ixabepilone DRP. Details of how the DRP was applied, the eligibility criteria, and the characteristics of participants are not reported in the registry record.

The primary outcome description indicates an intended comparison against a historic control and repeated comparisons for subgroups defined by ER status. However, no historic-control result, subgroup result, or primary efficacy result is reported in the registry record. The question can therefore be described from the planned outcome, but the available record does not establish what clinical benefit was observed or how precisely it was estimated.

3. Trial Design

This is a phase II, open-label, single-group study of ixabepilone. Allocation is listed as not applicable, and masking is listed as none. These features mean the study is not described as a randomized, blinded, controlled trial. Enrollment is 13. The registry status is terminated; the recorded start date is 2021-03-01 and the primary completion date is 2024-12-01.

The population in the official title consists of patients with locally recurrent or metastatic breast cancer selected by the Ixabepilone DRP after failure of an anthracycline and taxanes. The brief summary likewise describes the aim as investigating ixabepilone's anti-tumor effect in this selected population. Further eligibility details, the recruitment setting, and participant demographic or disease characteristics are not reported in the registry record.

The intervention is ixabepilone injection. The arm description specifies 40 mg/m2 as a 3-hour intravenous infusion on Day 1 in a 3-week cycle. Treatment duration, dose-modification rules, and any other treatment details are not reported in the registry record.

The primary outcome is clinical benefit rate, assessed from baseline to 24 weeks using tumor measurements such as CT or MRI. Its description proposes one-sided comparisons with a historic control and repeats for ER-status subgroups. This planned historic comparison does not create a concurrent control arm; details of the historic data and the analysis are not reported in the registry record.

Other listed outcomes include progression-free survival, overall survival, overall response rate defined as CR plus PR, treatment-emergent adverse events measured by NCI-CTCAE v.5.0, and clinical benefit rate comparing fresh biopsy with archival material. The record lists six outcome measures and zero analysis results. A sample-size justification, planned analysis population, and detailed statistical analysis plan are 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 Clinical Benefit Rate (CBR), measured over Baseline to 24 weeks.

The primary outcome is titled clinical benefit rate (CBR), with a timeframe from baseline to 24 weeks. The description says it is evaluated using tumor measurements, for example CT or MRI. The registry record gives the unit as participants with partial response. That unit does not, by itself, clarify whether the reported endpoint includes any other response category or how clinical benefit is defined.

As a general statistical concept, a tumor-response endpoint can translate measurements into a clinically interpretable count or proportion of participants meeting prespecified criteria. Such an endpoint can be useful for describing anti-tumor activity in an early-phase study. Its interpretation depends on the response definitions, assessment schedule, and rules for handling missing or unevaluable scans. Those details are not reported in the registry record.

The distinction between the endpoint title and its stated unit matters: the record names CBR, while the unit refers to participants with partial response. The secondary outcome list separately defines overall response rate as CR plus PR. The registry does not give a complete CBR definition, criteria for stable disease, or a threshold for duration of benefit. It also does not report an observed CBR result or an uncertainty interval. Therefore, the endpoint's intended measurement can be described, but its exact operational definition and observed estimate cannot be established from the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The statistical information in the registry record is limited. It identifies a single-group design, a primary outcome timeframe, and an intended one-sided comparison with a historic control, repeated for ER-status subgroups. It does not report the completed analysis methods or results. The concepts below explain how such methods are generally interpreted; they do not establish which procedures were carried out in this study.

What does a single-group design estimate?

In a single-group study, an outcome can be described among participants who receive the intervention. For a binary outcome, a common summary is the number of participants meeting the outcome definition, sometimes accompanied by a proportion and an uncertainty interval. Here, the primary outcome unit is described as participants with partial response, but the number meeting that definition and any corresponding estimate are not reported in the registry record.

General statistical explanation: uncertainty intervals help show how much an estimate might vary because the study includes a limited amount of information. A narrow interval indicates more precision than a wide interval, while neither interval nor point estimate alone resolves design limitations. No primary-outcome confidence interval is reported in the registry record.

What would a historic-control comparison require?

The primary outcome description says one-sided comparisons with a historic control would be performed. A one-sided test generally evaluates evidence in a specified direction rather than treating departures in both directions symmetrically. The direction, test statistic, significance threshold, and completed test result are not reported in the registry record.

General statistical explanation: a historic comparison uses data collected outside the study's concurrent treatment group. Its interpretation depends on whether the historical participants, outcome definitions, measurement practices, and follow-up are sufficiently comparable. Differences in these features can complicate attribution. The identity and source of the historic control, its sample size, and its outcome data are not reported in the registry record.

The description also says the comparison would be repeated in ER-status subgroups. Subgroup analyses can ask whether an outcome pattern differs across prespecified participant categories, but subgroup estimates can be less precise when fewer participants contribute to each group. The subgroup definitions, numbers in each subgroup, and results are not reported in the registry record.

What does the planning illustration mean?

The planning assumptions describe a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. They also define the effect to detect as a stated fraction of the observed effect. These are assumptions for a planning illustration, not a description of the single-group trial's allocation. No numerical sample-size estimates are reported in the registry record, and the trial's own sample-size justification is not reported in the registry record.

General statistical explanation: a sample-size calculation estimates how many participants would be needed under specified assumptions to detect a chosen effect with a chosen operating characteristic. A planning illustration is conditional on those assumptions. It is not observed power, does not establish the probability that a completed trial's result is true, and does not substitute for an outcome estimate or confidence interval. Since the illustration uses an effect tied to an observed effect, interpretation also requires knowing that effect and the calculation inputs; these are not reported in the registry record.

How should the event counts be understood?

The primary outcome is expressed as a count of participants with an event, and the safety information also gives participant counts and percentages. General statistical explanation: binary-outcome analyses distinguish the number meeting an outcome from the number assessed. A percentage or rate can be interpreted only with its denominator and outcome definition. The safety record reports 13 participants at risk in the listed group, but efficacy denominators and missing-outcome handling are not reported in the registry record.

For time-to-event outcomes such as progression-free survival and overall survival, statistical methods commonly account for follow-up duration and censoring, rather than treating every participant as if observed for the same length of time. This is a general explanation, not a claim about the study's analysis. The record names these secondary outcomes but does not report their event counts, estimates, follow-up summaries, or analysis methods.

Over-dispersion is a general concern when count data vary more than a model assumes; ignoring it can make uncertainty appear too small. It is not possible to determine from the registry record whether over-dispersion is relevant here, because no count-model method or such analysis is reported.

Overall, the registry record supports a description of the design and planned outcome, but does not disclose enough analysis detail to reproduce or evaluate a completed efficacy analysis. The statistical test, confidence-interval method, covariate adjustment, missing-data approach, and analysis population 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("Ixabepilone")
n      <- c(13)
events <- c(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  Ixabepilone  13  2  15.4  1.9  45.4  4.3  42.2  4.7  42.8

11. Multiplicity, Missing Data and Analysis Populations

The registry record names multiple outcomes: clinical benefit rate, progression-free survival, overall survival, overall response rate, treatment-emergent adverse events, and a clinical-benefit comparison between fresh biopsy and archival material. It also describes repeating the primary historic-control comparison for ER-status subgroups. The record does not report a multiplicity strategy, such as a hierarchy of outcomes or an adjustment for multiple statistical tests.

General statistical explanation: when several hypotheses are tested, the chance of at least one apparently notable result can increase unless the analysis plan accounts for multiple testing. This concern can apply to several outcomes and subgroup comparisons. The number and sequence of completed tests, and any multiplicity adjustment, are not reported in the registry record. No efficacy analysis results are reported.

The registry record does not report how missing tumor assessments, participants who discontinue treatment, or participants without a response assessment were handled. It does not state whether the primary analysis included all enrolled participants, only treated participants, or only those with evaluable scans. The analysis population is not reported in the registry record.

General statistical explanation: missing outcome data can affect an estimate if the likelihood of having an assessment is related to a participant's outcome. The potential effect depends on why data are missing and on the analysis method. Without the number of assessments, reasons for missingness, and handling rules, the impact cannot be evaluated for this study. The reason the study was terminated is also not reported in the registry record.

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 5% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: tremor (7.7%), anaemia (7.7%), neutropenia (7.7%), general physical health deterioration (7.7%), asthenia (7.7%).

The safety record lists 13 participants at risk in the ixabepilone group. Serious adverse events affected 4 participants; other adverse events affected 13 participants; deaths are listed as 0. These are participant-level summary figures in the registry record, not comparisons between treatment groups.

The listed serious adverse-event terms are tremor, anaemia, neutropenia, general physical health deterioration, asthenia, and dyspnoea. Each term is reported at 7.7%. The record does not give further detail about event timing, duration, severity grades, recurrence, or whether the same participant experienced more than one term. These percentages should therefore be read as the reported term-specific figures, not combined into a total.

The secondary outcome description says treatment-emergent adverse events were measured by NCI-CTCAE v.5.0. The registry record does not report exposure duration, a concurrent safety comparator, or the analysis method. A count of participants with events describes what was recorded in this group; it does not establish that ixabepilone caused an event or indicate how the figures compare with another treatment.

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

The posted information establishes that the study investigated ixabepilone in a selected population with locally recurrent or metastatic breast cancer after anthracycline and taxane failure. It also establishes that the design was open-label and single-group, that enrollment was 13, and that the study is listed as terminated. The registry record reports some safety counts and identifies a planned primary outcome and secondary outcomes.

It does not establish the observed primary clinical benefit rate. No efficacy analysis results, confidence intervals, or p-values are reported in the registry record. Although the primary outcome description mentions a historic-control comparison and ER-status subgroups, the record does not report results for those comparisons. It is therefore not possible to determine the size, direction, or precision of an efficacy estimate from the posted information.

General statistical interpretation: a single-group outcome can describe what happened among participants in that group, but without a concurrent control it does not by itself distinguish treatment effects from other influences. A historic comparison may add context, but its interpretation depends on the source and comparability of the historical data. Those details and results are not reported in the registry record.

The safety counts are descriptive and are not comparative estimates. They should not be used to infer that an event was caused by treatment, to compare treatments, or to draw conclusions about risk beyond the recorded group. The reason for termination, treatment exposure, and completeness of safety follow-up are not reported in the registry record.

Accordingly, the record supports a careful account of the trial's design, target population, intended outcome, and reported safety figures. It does not support a conclusion about the clinical effect of ixabepilone or the precision of an efficacy estimate. Missing analysis results are not evidence of either benefit or lack of benefit.

14. Why This Trial Matters Statistically

This study raises a useful statistical question about how a biomarker-selected single-group trial can describe outcomes in a population defined by prior treatment failure and selection with the Ixabepilone DRP. The primary outcome description also proposes a historic-control comparison and ER-status subgroup comparisons. These features make the choice and reporting of comparator data, subgroup definitions, and endpoint criteria especially important to interpreting any eventual estimates.

The record illustrates the difference between a planned clinical question and a reported statistical result. It identifies clinical benefit rate from baseline to 24 weeks as the primary outcome, but does not report an efficacy analysis. It also names progression-free survival, overall survival, overall response rate, adverse events, and a fresh-biopsy-versus-archival comparison without reporting their results. A list of outcomes alone cannot show what was observed or how precisely it was estimated.

Enrollment of 13 participants makes transparent reporting of the analysis population, outcome counts, and uncertainty particularly relevant. General statistical explanation: in a study with a limited number of observations, individual outcomes can have a substantial influence on a group estimate, so counts and intervals help readers judge its stability. Those efficacy counts and intervals are not reported in the registry record.

The record also demonstrates why a planning calculation should be distinguished from an analysis of trial data. The planning assumptions describe a two-arm illustration, while the actual design is single-group. Any numerical planning estimate would depend on its assumptions and would not constitute observed power or an efficacy finding. No numerical planning estimates are reported in the registry record.

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 principal limitation for statistical interpretation is the absence of reported efficacy results. The registry record does not give the primary outcome count or estimate, uncertainty interval, or comparison result. It lists zero analysis results despite naming multiple outcomes. The reason for termination and whether the planned analyses were completed are not reported in the registry record.

The primary endpoint's description leaves an operational ambiguity: it is titled clinical benefit rate but gives the unit as participants with partial response. The record does not report a full definition of clinical benefit, response criteria, assessment schedule, independent review procedures, or rules for confirming response. It also does not report how missing or unevaluable tumor assessments were handled.

The single-group design has no concurrent control arm. A historic comparison is mentioned, but the historical source, eligibility rules, outcome definitions, and comparability are not reported in the registry record. The record does not provide the ER-status subgroup definitions or results, or explain how multiple outcomes and subgroup tests were handled.

Enrollment was 13, but the number included in each efficacy analysis is not reported in the registry record. Participant characteristics, treatment duration, follow-up completeness, dose changes, and reasons for discontinuation are also not reported. These omissions limit assessment of who contributed data and how representative the analyzed group may have been.

The safety information is a descriptive summary without a concurrent comparator or reported exposure duration. Details on event timing, severity, and attribution are not reported in the registry record. The planning assumptions are described, but no numerical sample-size estimates or trial-specific sample-size justification are reported. Together, these gaps prevent a complete assessment of the study's statistical precision and the robustness of any efficacy interpretation.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Anti-tumor Effect of Ixabepilone in Metastatic Breast Cancer (mBC) Selected by the Ixabepilone DRP. — NCT04796324.
• Registry record last updated 2026-03-12; status last verified 2026-03.
• Results first posted 2026-03-12.
• 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

NCT04796324 is a phase II, open-label, single-group study of ixabepilone in patients with locally recurrent or metastatic breast cancer selected by the Ixabepilone DRP after failure of an anthracycline and taxanes. Enrollment was 13. The regimen is described as 40 mg/m2 by a 3-hour intravenous infusion on Day 1 of a 3-week cycle. The registry lists the study as terminated.

The primary outcome is clinical benefit rate from baseline to 24 weeks, with the unit described as participants with partial response. The record mentions intended one-sided comparisons with a historic control and ER-status subgroups, but reports no efficacy analysis results. Safety information includes 4 participants with serious adverse events, 13 with other adverse events, and 0 deaths. The reason for termination and further analysis details are not reported in the registry record.