Clofarabine Plus Low-Dose Cytarabine for Patients With Higher-Risk Myelodysplastic Syndrome (MDS): Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Clofarabine Plus Low-Dose Cytarabine for Patients With Higher-Risk Myelodysplastic Syndrome (MDS) (NCT01444742), a na phase 2 study. The primary outcome is Number of Participants With Complete Response (CR).

2. Clinical Question

The clinical question is about response and safety in a specific treatment setting: higher-risk MDS after failure of hypomethylator therapy. The outcome is a count of participants meeting the complete-response definition, not a comparison of response rates between treatment groups. Because the study has one group, its results would describe outcomes among participants in that group; they would not, on their own, estimate how outcomes would differ under another treatment.

The record also lists overall survival as a secondary outcome. It does not report an overall-survival result in the information available in the registry record. The primary response timeframe is 4 weeks after the first cycle, while the response definition separately requires the response to persist for at least 4 weeks. These details describe what was intended to be measured; they do not establish that a particular response count or survival outcome was observed.

3. Trial Design

This was a phase 2, single-group clinical study sponsored by M.D. Anderson Cancer Center. The registry lists enrollment as 81 and status as completed. The study began on 2011-11-16, and primary completion was recorded as 2017-01-29. Allocation is listed as not applicable, and masking as none. These features describe the design; they do not indicate a randomized comparison.

The intervention group is titled Clofarabine + Cytarabine. For induction, the record describes clofarabine 10 mg/m2 by vein over 1-2 hours daily for 5 days, on days 1-5, with cytarabine 20 mg subcutaneously twice daily for 7 days, on days 1-7. For consolidation, it describes clofarabine 10 mg/m2 by vein over 1-2 hours daily for 3 days, on days 1-3, with cytarabine 20 mg subcutaneously twice daily for 5 days, on days 1-5. These are the recorded regimen details, not evidence that every participant received every planned dose or phase.

A single-group design can describe the outcomes observed in the enrolled group. It cannot make a like-for-like treatment comparison because there is no concurrent control group. In general, a treatment contrast requires an appropriate comparison: differences in outcomes between separate groups can reflect differences in their underlying characteristics or circumstances as well as differences in treatment. The registry specifically identifies this study as not being a randomized comparison.

The primary outcome is the number of participants with complete response, with assessment described at 4 weeks after the first cycle. Overall survival is listed as a secondary outcome. The registry record does not report the response count, an overall-survival estimate, or outcome analyses. It also does not report details of the sample-size justification, interim analyses, or a broader 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: Of the 81 participants registered, one participant was never treated with the study medication. All Participants were registered at The University of Texas MD Anderson Cancer Center.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: One of the eighty-one participants registered on the study were in evaluable for response.

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 Complete Response (CR), measured over 4 weeks after first cycle.

The primary endpoint is the number of participants with complete response. It is a count-based outcome: each participant is classified according to whether the response criteria are met, and the reported endpoint is the number meeting those criteria. The registry gives the timeframe as 4 weeks after the first cycle and specifies that a complete response must last for at least 4 weeks.

The recorded criteria combine findings from marrow and blood. They include marrow myeloblasts at <= 5% with normal maturation of all cell lines, while persistent dysplasia may be noted. Blood criteria include hemoglobin >= 11 g/dL when untransfused and not on EPO; neutrophils >= 1x109/L without myeloid growth factor; platelets >= 100 * 109/L without a thrombopoietic agent; and no blasts. The record says that a bone marrow aspirate and/or biopsy was to be performed at the end of course 1, on day 28 +/- 7 days.

In general, a defined response endpoint helps make the outcome rule explicit: readers can see which clinical and laboratory features qualify as a response and when assessment is intended to occur. A count of responses is descriptive unless accompanied by a denominator and analysis that support further interpretation. Here, the primary response count is not reported in the registry record, so the endpoint definition can be described but the observed response result cannot be assessed.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

Clinical trial methods determine how participants enter a study, how outcomes are defined, and what kinds of conclusions the results can support. In this study, the registry identifies a phase 2, single-group design, with allocation listed as not applicable and masking as none. The study has one intervention group, Clofarabine + Cytarabine. These design features shape interpretation: the record describes outcomes in a treated study group, rather than a randomized contrast between groups.

What does a single-group design estimate?

In general, a single-group study can report the number or proportion of participants who meet a specified outcome rule during a stated period. Such a result is descriptive of the study group and the conditions under which it was observed. A control group is needed for a direct comparison within the trial. Without one, the study cannot isolate a treatment effect from other explanations for observed outcomes, such as differences in participant characteristics or the course of disease. This is why a single-group result should not be expressed as a randomized treatment advantage.

The registry lists 81 participants enrolled. Its primary outcome is a participant count with complete response, assessed 4 weeks after the first cycle. A count and a rate answer different descriptive questions: a count records how many participants met the rule, while a rate relates that count to a defined analysis population. The response count is not reported in the registry record, and the registry’s description of the response-evaluable population is unclear. Consequently, the outcome cannot be reconstructed from the available record.

How is complete response defined?

The response rule combines marrow and blood findings and requires the response to last at least 4 weeks. The record specifies marrow myeloblasts at <= 5% with normal maturation of all cell lines, and notes that persistent dysplasia may be present. Blood criteria include hemoglobin >= 11 g/dL when untransfused and not on EPO; neutrophils >= 1x109/L without myeloid growth factor; platelets >= 100 * 109/L without a thrombopoietic agent; and no blasts. It describes a bone marrow aspirate and/or biopsy at the end of course 1, on day 28 +/- 7 days.

In general, explicit endpoint criteria reduce ambiguity by specifying the findings that qualify as an event and the assessment time. They also make the analysis dependent on the availability and interpretation of the required measurements. The registry record does not explain how incomplete assessments, missing laboratory values, or participants who could not be evaluated were handled. Those decisions can affect which participants contribute to an endpoint analysis, so they should be reported rather than assumed.

What does the response-monitoring method tell us?

The record states that the method of Thall, Simon, and Estey was used to monitor response. This identifies a named method but does not give the implementation details. The decision rules, monitoring schedule, statistical assumptions and any resulting decisions are not reported in the registry record. It is therefore not possible to describe how monitoring operated or to infer whether an interim analysis took place. The name of a method alone does not supply those missing details.

How should precision be understood?

In general, a confidence interval communicates uncertainty around an estimate under specified statistical assumptions. A narrower interval indicates greater precision under those assumptions; a wider interval indicates less precision. The interval does not remove limitations in the design or show that a result applies to people outside the study. No confidence interval or other uncertainty estimate for complete response is reported in the registry record. Since the response count is also absent, there is no primary estimate to interpret for precision.

For a count-based endpoint, the denominator and analysis population matter. The number enrolled is not necessarily the same as the number included in every endpoint analysis. The registry’s response-population wording is unclear, and the endpoint result is not reported. It would be inappropriate to assume that all registered participants were evaluable or to infer an analysis denominator from the enrollment entry.

What do the planning illustrations mean?

In general, a sample-size planning calculation asks how many participants a future study might require under specified assumptions about the effect to detect, the significance level, allocation and statistical method. It is a planning exercise, not an observed result and not a statement of the probability that a completed study detected an effect. The registry’s planning assumptions describe an illustration based on an observed effect, two-sided significance level 0.05, equal allocation between two arms, and a normal approximation; the effect to detect is expressed as a fraction of the observed effect. For time-to-event outcomes the stated approach concerns total events, while other outcomes concern participants per arm.

The numerical planning scenarios and the observed effect used for them are not reported in the registry record available for this analysis. The record also does not report the study’s own sample-size justification. The planning assumptions therefore cannot be used to claim that this study was designed with a particular power or that it had a particular probability of detecting an effect. Sample-size illustrations for a hypothetical two-arm study do not change the fact that the registered trial is single-group.

Finally, the registry lists overall survival as a secondary outcome but does not report its analysis. Time-to-event methods generally account for the timing of events and for participants whose event time is not observed during follow-up. The specific method, follow-up information and survival result are not reported in the registry record, so those methods cannot be attributed to this study on the basis of the available information.

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("Clofarabine + Cytarabine")
n      <- c(80)
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  Clofarabine + Cytarabine  80  19  23.8  14.9  34.6  15.8  34.1  15.8  34.2

11. Multiplicity, Missing Data and Analysis Populations

The registry lists the number of participants with complete response as the primary outcome and overall survival as a secondary outcome. It identifies two outcome measures but does not report outcome analyses in the available record. The registry record does not describe a multiplicity strategy, such as how interpretation would account for examining more than one outcome. That information is not reported in the registry record.

In general, multiplicity arises when several outcomes, comparisons or analyses are considered. Examining more than one result can increase the chance of a seemingly notable finding arising by chance, depending on the analysis plan and inferential approach. A prespecified strategy helps readers distinguish the primary question from additional analyses. The record does not state whether adjustment or another approach was planned, so none should be assumed.

Missing-data handling is also not reported in the registry record. In general, missing outcome assessments may affect an analysis if participants with unavailable measurements differ from those whose outcomes are observed. Relevant details include how missing assessments were classified, whether participants were excluded from an endpoint analysis, and what assumptions were used. The record’s description of the response-evaluable population is unclear, and no clear analysis-population definition is available.

Enrollment is reported as 81, but this does not establish the denominator for every outcome. The primary response count and its analysis denominator are not reported. The listed safety counts have their own stated at-risk numbers; they should not be used to infer the response-analysis population. The registry also does not report whether sensitivity analyses were performed to examine missing data or alternative analysis populations.

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: neutropenic fever (30.9%), lung infection (27.2%), infection (8.6%), sepsis (8.6%), hemorrhage (4.9%).

The safety record lists one group, Clofarabine + Cytarabine, with 81 participants at risk for the serious-adverse-event measure and 57 affected. For other adverse events, it lists 81 at risk and 46 affected. The record also lists 16 deaths. These figures describe the posted safety data; they do not establish how events compare with another treatment because the study has no concurrent comparator group.

The selected serious adverse-event terms and percentages are Neutropenic Fever, 30.9%; Lung Infection, 27.2%; Infection, 8.6%; Sepsis, 8.6%; Hemorrhage, 4.9%; and Death, 3.7%. These are term-specific percentages as recorded. The registry does not explain whether participants could appear under more than one term, so the entries should not be added or treated as mutually exclusive. The term-specific percentage for Death should also not be treated as interchangeable with the separate count of deaths; the record does not provide enough detail to equate those measures.

In general, safety counts describe how many participants had recorded events in the defined group. They do not by themselves establish that the treatment caused an event, and they do not show comparative risk without an appropriate comparator and analysis. Details on event ascertainment, severity grading and the relationship between event categories are not reported in the registry record.

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

The registry record establishes that a completed phase 2, single-group study examined clofarabine plus cytarabine in people with higher-risk MDS after relapse following, or refractoriness to, hypomethylator therapy. It provides an induction and consolidation regimen, defines complete response, and lists selected safety counts and terms. Those details describe the study and the posted data; they do not answer the primary clinical question because the complete-response count is not reported.

The record does not report an overall-survival result, despite listing overall survival as a secondary outcome. It also does not report an analysis of the primary endpoint or uncertainty estimates. The absence of these results in the registry record should not be interpreted as a positive or negative outcome. No conclusion about the response rate or survival can be drawn from an endpoint definition alone.

The safety figures are descriptive counts and percentages for the single group. Without a concurrent comparator, they cannot show whether the listed events were more or less frequent than under another treatment. Nor do the figures, by themselves, establish that the intervention caused any particular event. The registry does not report the additional details needed to interpret event overlap, severity grading or causal attribution.

In general, a treatment effect is a contrast between outcomes under different treatment conditions. A single-group study does not observe that contrast directly. Even a clearly measured outcome in the study group would not establish what would have happened to comparable participants under a different approach. The design therefore supports description of the group and its recorded outcomes, not a randomized comparative claim.

The registry mentions a response-monitoring method and includes planning assumptions for sample-size illustrations. It does not report the method’s implementation, the study’s own sample-size justification, or numerical planning scenarios in the available record. Those details cannot fill the gap left by unreported outcome results. The most defensible reading is that the record documents the trial’s intended question and some safety data, while leaving the primary response and survival findings unavailable.

14. Why This Trial Matters Statistically

This study is statistically important to read as a single-group phase 2 trial rather than as a comparative treatment test. The distinction determines what the design can estimate. A single group can be described in terms of its observed outcomes, while a direct estimate of comparative effect requires an appropriate contrast. Keeping that distinction clear prevents descriptive safety counts or a defined response endpoint from being mistaken for evidence of a treatment difference.

The complete-response endpoint illustrates why outcome definitions matter. The registry specifies marrow and blood criteria, a response duration requirement, and an assessment time after the first cycle. These details make the intended outcome more interpretable than a loosely defined label. At the same time, a precise definition cannot replace the observed result: the response count is not reported in the registry record, and its description of the evaluable population is unclear.

The safety data also illustrate the importance of reading categories carefully. Counts for serious and other adverse events, deaths, and selected event terms answer different descriptive questions. Their denominators and overlap should not be assumed to be identical. Without a concurrent comparator and fuller reporting of event definitions, the figures should not be converted into comparative conclusions.

Finally, the registry identifies a response-monitoring method and planning assumptions, but does not report enough information to reconstruct the statistical implementation or the study’s own sample-size rationale. This is a useful reminder that a named method or planning framework is not equivalent to a complete analysis plan. Transparent reporting of analysis populations, missing-data handling, uncertainty and outcome estimates is necessary for readers to judge how much the data establish.

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 primary limitation for interpreting efficacy is that the registry record does not report the primary outcome result. The number of participants with complete response is not available, nor is a confidence interval or other precision estimate. Overall survival is listed as a secondary outcome, but its result and analysis are also not reported. This prevents assessment of the stated clinical outcomes from the available record.

The study is single-group, with no concurrent comparator. Accordingly, even if outcome estimates were reported, the design would not support a randomized comparison with another treatment. The registry’s response-population description is grammatically unclear, so the analysis population and denominator for the primary endpoint cannot be established. Missing-data procedures, sensitivity analyses and the handling of participants not evaluable for response are not reported in the registry record.

Further statistical details are also absent. The registry does not report the implementation of the named response-monitoring method, interim-analysis details, a multiplicity strategy, the study’s sample-size justification, or numerical planning scenarios in the available record. It does not provide the information needed to assess uncertainty for the primary result because that result is not posted.

For safety, the record supplies group-level counts and selected serious adverse-event terms, but does not report details on overlap among terms, event severity grading, or causal attribution. These limitations restrict interpretation of the safety entries and make comparative safety claims inappropriate. The posted information is therefore useful for describing the registered design and selected safety data, but insufficient to quantify the primary response outcome or establish comparative effects.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Clofarabine Plus Low-Dose Cytarabine for Patients With Higher-Risk Myelodysplastic Syndrome (MDS) — NCT01444742.
• Registry record last updated 2018-07-03; status last verified 2018-06.
• Results first posted 2018-05-31.
• 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 record describes a completed phase 2, single-group study of clofarabine plus cytarabine for higher-risk MDS after relapse following, or refractoriness to, hypomethylator therapy. Enrollment is listed as 81. Allocation is not applicable, and masking is none. The primary endpoint is the number of participants with complete response, assessed 4 weeks after the first cycle; the response count is not reported in the registry record. Overall survival is listed as a secondary outcome, without a reported result.

The record describes induction and consolidation schedules and lists safety counts for the Clofarabine + Cytarabine group: 57 of 81 affected by serious adverse events, 46 of 81 affected by other adverse events, and 16 deaths. It also lists selected serious adverse-event terms and percentages. These are descriptive data from a single-group study, not a randomized comparison. The registry does not report the response-analysis population clearly, the handling of missing data, or the detailed statistical implementation.