A Study to Evaluate the Efficacy, Safety and Pharmacokinetics of Emapalumab in Adult Patients With HLH: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for A Study to Evaluate the Efficacy, Safety and Pharmacokinetics of Emapalumab in Adult Patients With HLH (NCT03985423), a na phase 2, phase 3 study. The primary outcome is Overall Response.

2. Clinical Question

The clinical question was whether emapalumab could be assessed for efficacy, safety, and pharmacokinetics in adults with secondary HLH. The primary endpoint was intended to capture improvement across clinical and laboratory features of HLH, rather than change in a single measurement. Because the record reports no collected primary efficacy data and has no comparator group, it cannot establish a comparative effect on response. The safety information describes events recorded in the treated group, but without a control group it cannot distinguish events associated with treatment from events related to HLH or other causes.

3. Trial Design

This was a Phase 2/3, open-label, single-arm, multicenter study sponsored by Swedish Orphan Biovitrum. The registry lists an enrollment of 7 and identifies the condition as hemophagocytic lymphohistiocytoses. The study began on 2020-06-02; primary completion is listed as 2021-06-29, and the current status in the record is terminated.

Participants received emapalumab-Lzsg by intravenous infusion. The described regimen began with 6 mg/kg and continued at 3 mg/kg every 3 days for the first 2 weeks, then twice a week. The arm description also begins to state that the treating physician could deem a dose change appropriate, but the text is cut off. The full dose-modification approach is not reported in the registry record.

Open-label means that treatment assignment was not masked. Since there was no randomized allocation and only a single treatment group, there is no parallel control group in this record. Safety observations can describe what was recorded among treated participants, but the design does not provide a like-for-like comparison with untreated participants or another treatment.

The registry lists overall response at Week 4 as the primary outcome. It also lists secondary outcomes including best response on treatment, overall response, overall survival, time to complete or partial response, duration of response, relapse, adverse events, and serum emapalumab concentrations. Although the registry lists 11 outcome measures, it reports no primary efficacy endpoint data because the study was prematurely terminated. Detailed analysis populations, follow-up completeness, and a 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.

Before assignment: The study consisted of a screening (up to 2 weeks), treatment period (until clinically satisfactory response was achieved), and follow-up period (1 year). A total of 7 patients were enrolled in the study and treated.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Since the study was prematurely terminated, no data was collected for the primary efficacy endpoint.

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.

Population: The All Treated analysis set included all patients who received at least 1 dose or 1 incomplete dose of emapalumab.

6. Primary Endpoint

The registry lists the primary outcome as Overall Response, measured over Week 4.

The primary endpoint was overall response at Week 4, defined as achieving either complete response or partial response. Complete response required a specified pattern across HLH findings: no fever, normal spleen size, no cytopenia, no hyperferritinemia, no evidence of coagulopathy, no neurological and cerebrospinal fluid abnormalities attributed to HLH, and no sustained worsening of soluble CD25. The registry gives thresholds for several of these criteria, including body temperature <37.5°C, absolute neutrophil counts >=1.0x10^9/L, platelet count >=100x10^9/L, serum ferritin <2000 µg/L, and fibrinogen >150 mg/dL where used to indicate normal levels. Absence of growth-factor and transfusion support had to be documented for at least 4 days to report no cytopenia. Sustained worsening of sCD25 was defined by at least two consecutive measurements >2-fold higher than baseline.

Partial response required improvement, defined as a >50% change from baseline or normalization, in at least 3 HLH clinical and laboratory criteria, including central nervous system abnormalities. In general, a composite endpoint can represent improvement across multiple disease features when no single measure captures the clinical picture. Its interpretation depends on how the component criteria are defined and applied. The registry record reports no collected data for this primary efficacy endpoint, so it supplies no observed response result to interpret.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does a single-arm design estimate?

In general, a single-arm study can describe outcomes observed among participants receiving the study intervention. If outcomes are collected, the observed proportion meeting a response definition can be estimated for that group, with uncertainty reflecting the amount and variability of the data. Such a description is not the same as a treatment effect relative to a comparator. Without a comparison group, differences from an external expectation may reflect differences in patient characteristics, disease course, other care, outcome assessment, or follow-up as well as any intervention effect.

For this study, the registry record identifies a single group and no allocation. It reports that no data was collected for the primary efficacy endpoint. Therefore, the usual descriptive estimate for overall response at Week 4 cannot be derived from the record. An analysis cannot recover an observed response rate from the endpoint definition alone.

How should a binary response endpoint be understood?

Overall response is defined as meeting either the complete-response or partial-response criteria. In general, a binary endpoint classifies each assessed participant as meeting or not meeting a prespecified outcome definition. A response proportion is interpretable only with clear information about who was assessed, the outcome time point, how missing assessments were handled, and the exact criteria applied. The registry gives detailed clinical and laboratory criteria, but reports no collected primary endpoint data. The number assessed, missing-data handling, and any endpoint adjudication procedures beyond the description are not reported in the registry record.

A confidence interval, in general, expresses the statistical uncertainty around an estimated quantity under a specified method. It does not repair missing outcome data or remove bias from an uncontrolled design. No primary response estimate or interval is reported in the registry record, so no precision assessment for the primary outcome can be made from it.

Why does the absence of a comparator matter?

In a randomized comparison, groups are formed to support a contrast between outcomes under different assigned treatments. This study had no randomized comparison, and its allocation is listed as not applicable. Its safety and other observed outcomes therefore describe the treated group rather than a comparative effect. General explanation: an uncontrolled observation can be affected by selection, concurrent care, natural disease changes, and the way outcomes are measured. A single-arm result should not be interpreted as if it were a randomized treatment contrast.

How should the sample-size assumptions be read?

The planning assumptions describe an illustration based on an observed effect, using a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. The effect to detect is described as a stated fraction of the observed effect. For time-to-event calculations, the stated convention is total events; for other calculations, it is participants per arm. These are planning assumptions, not the design actually used in this single-arm trial. Sample-size illustrations are not observed power, and they do not demonstrate that a treatment effect exists. The primary endpoint result is not reported in the registry record, so any illustration that depends on an observed effect must be interpreted in light of the outcome and estimate on which it is based.

What can be inferred from the safety counts?

The adverse-event information is descriptive. It records numbers of participants affected in the emapalumab group and lists selected serious-event terms as percentages. In general, a count or proportion in a small study can be unstable: a small change in the observed data can change the estimate substantially. In addition, without a comparator, these counts cannot quantify excess risk attributable to treatment. The registry record does not report confidence intervals, exposure-adjusted rates, or a causal analysis for the adverse-event figures.

Over-dispersion is a general statistical issue that arises when outcome variability is greater than a simple model assumes. If relevant, accounting for it can prevent uncertainty from being understated. The registry record does not report a model or analysis addressing over-dispersion, and the primary efficacy endpoint has no collected data. It would therefore be inappropriate to claim that a particular model was used or that its assumptions were checked.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists 11 outcome measures, including the primary overall-response endpoint and secondary outcomes such as overall survival, response timing and duration, relapse, adverse events, and serum concentrations of emapalumab. When multiple outcomes or repeated analyses are considered, general statistical practice recognizes a multiplicity issue: the more opportunities there are to identify a statistically notable result, the more important it is to interpret findings in the context of a prespecified analysis plan. The registry record does not report a multiplicity adjustment or a statistical analysis plan. It is therefore not possible to determine from this record how multiple outcomes were prioritized or how any testing across them was handled.

The primary efficacy endpoint has no collected data because the study was prematurely terminated. The registry record does not describe the reason for termination, what data were available for each secondary outcome, or how missing measurements were handled. It also does not report the analysis populations, such as whether analyses were planned for all enrolled participants, treated participants, or participants with an evaluable assessment. These omissions matter because the interpretation of an outcome depends on who contributed data and how incomplete follow-up was treated.

General explanation: missing outcome data can reduce precision and can introduce bias if the probability of missingness is related to disease status, treatment, or other factors. Different missing-data assumptions can lead to different conclusions. Since the record does not report a missing-data strategy or primary outcome data, no such assumptions can be assessed for the primary endpoint. The enrollment figure alone does not establish the number with data for any particular secondary outcome.

The safety counts are reported, but details about the observation period, event timing, and participant exposure are not included in the record summarized. The absence of these details limits interpretation of event rates and follow-up completeness. No claim about a prespecified interim analysis or analysis stopping rule is supported by the registry record.

11. 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 0% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: acute myeloid leukaemia (14.3%), febrile neutropenia (14.3%), lymphoma (14.3%), bacteramia (14.3%), cytomegalovirus hepatitis (14.3%).

The registry reports serious adverse events affecting 5 of 7 participants in the emapalumab group. Other adverse events affected 7 of 7 participants, and 4 deaths are reported. The listed serious-event terms—acute myeloid leukaemia, febrile neutropenia, lymphoma, bacteramia, cytomegalovirus hepatitis, and fungaemia—are each reported at 14.3%.

These figures describe events recorded in the study group; they do not by themselves show that emapalumab caused an event. The study has no comparator group, and the registry information does not separate the contributions of treatment, HLH, underlying conditions, or other care. It also does not report the timing of the events, the duration of participant exposure, or whether the listed serious-event terms represent all serious events or selected terms beyond the stated top list. The percentages should therefore be read as descriptive registry figures, not as comparative or causal estimates. The record does not provide enough information to assess how complete safety follow-up was or how adverse events were attributed.

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

The record establishes that a Phase 2/3, open-label, single-arm study of emapalumab in adults with secondary HLH was terminated. It documents a planned primary outcome—overall response at Week 4—and gives criteria for complete and partial response. It also reports safety counts for the emapalumab group. These registry entries describe the study’s intended question and the information available in the registry record.

It does not provide an observed result for the primary efficacy endpoint. The registry explicitly states that no data was collected for that endpoint because the study was prematurely terminated. Thus, the record cannot estimate the primary response proportion, its precision, or a comparative treatment effect. The absence of a result is not evidence for either benefit or lack of benefit.

The safety information shows that adverse events and deaths were recorded among participants in the treated group. In a single-arm study, those observations cannot determine whether events occurred more or less often because of treatment. The record also does not report enough contextual detail to attribute the events or assess their timing and relation to exposure.

In general, a clinical trial’s design and completeness of outcome data determine which questions can be answered. A single-arm design may describe outcomes among treated participants, but it cannot supply a randomized comparison. Missing primary efficacy data further prevents interpretation of the principal efficacy question. Any planning calculations based on observed effects are illustrations under assumptions, not observed power or a substitute for the unavailable endpoint result. The appropriate reading is therefore limited: the registry documents the trial design, response criteria, termination, and reported safety observations, but does not establish an efficacy conclusion.

13. Why This Trial Matters Statistically

This trial is statistically notable for the gap between a clearly specified primary endpoint and the absence of collected data for that endpoint. The response definition spans fever, spleen size, blood counts, ferritin, coagulation, neurological and cerebrospinal fluid findings, and sCD25. The registry also specifies thresholds and a definition for partial response. Such detail makes clear what the planned outcome meant, but a detailed definition cannot replace outcome observations.

The study also illustrates the limits of inference from an open-label, single-arm design. Even with complete follow-up, outcomes in a treated group alone would not provide a randomized estimate of how outcomes compare with another treatment or with no study treatment. In this record, the primary efficacy result is unavailable as well, so the main response question cannot be assessed from the posted data.

Safety counts remain useful as descriptive information about what was reported in the study, but they are not a controlled comparison. This distinction is especially important when a disease may involve serious clinical events and the record does not provide causal attribution, timing, or exposure-adjusted rates. The figures can identify the types of events listed in the registry without establishing their cause.

The case also underscores that planned sample-size calculations and observed trial results answer different questions. A planning illustration depends on assumptions and an effect estimate; it does not recreate missing observations or establish that an effect was seen. Statistical interpretation must follow the data actually reported and the design that generated them.

14. 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 is the absence of collected data for the primary efficacy endpoint, overall response at Week 4. The registry attributes this to premature termination but does not report the reason for termination. It also does not report primary endpoint estimates, uncertainty intervals, participant-level response data, or the number assessed at the endpoint.

The study has no comparator group and no randomized allocation. This limits the ability to distinguish treatment-related changes from disease course, underlying conditions, supportive care, or other influences. The open-label design means masking was absent; the registry does not report whether endpoint assessment or adjudication was independently blinded.

Although the record lists secondary outcomes, it does not provide their results in the information summarized, nor does it describe the analysis populations, missing-data methods, multiplicity approach, or statistical analysis plan. The registry record also does not report the reason for any missing secondary measurements, if applicable, or the completeness and duration of follow-up for safety outcomes.

The arm description is incomplete after its statement about a treating physician deeming a dose change appropriate. The full dose-adjustment rules are therefore not reported in the registry record. For safety, the record gives counts and selected serious-event terms but does not report event timing, exposure-adjusted rates, or causal attribution. These limitations constrain both efficacy and safety interpretation.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: A Study to Evaluate the Efficacy, Safety and Pharmacokinetics of Emapalumab in Adult Patients With HLH — NCT03985423.
• Registry record last updated 2023-10-06; status last verified 2023-09.
• Results first posted 2023-10-06.
• 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.

18. Record Summary

This registry record describes a Phase 2/3, open-label, single-arm, multicenter study of emapalumab-Lzsg in adults with secondary HLH. Enrollment is listed as 7, and the study status is terminated. The planned primary endpoint was overall response at Week 4, based on complete or partial response criteria. The registry states that no data was collected for this primary efficacy endpoint because the study was prematurely terminated.

The emapalumab group safety record reports serious adverse events affecting 5 of 7 participants, other adverse events affecting 7 of 7, and 4 deaths. Selected serious-event terms are each listed at 14.3%. With no comparator and no primary efficacy result, the record supports a description of the trial and its reported safety observations, but not a comparative efficacy conclusion or causal safety estimate.