Extension Study to Evaluate the Safety and Tolerability of Tezepelumab in Adults and Adolescents With Severe, Uncontrolled Asthma: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Extension Study to Evaluate the Safety and Tolerability of Tezepelumab in Adults and Adolescents With Severe, Uncontrolled Asthma (NCT03706079), a randomized phase 3 study. The primary outcome is Exposure Adjusted Incidence Rates of AEs/SAEs.

2. Clinical Question

The clinical question is framed around safety and tolerability during an extension study. Participants had completed a predecessor study before being offered entry, so the registry record describes a population with prior study participation rather than a newly recruited group with no treatment history. The group labels distinguish participants by predecessor study and treatment history, including participants who switched from placebo to tezepelumab.

The study also lists Annualized Asthma Exacerbation Rate as a secondary outcome. That listing alone does not establish what the result was. Numerical results for that secondary outcome are not reported in the registry record. The available primary-outcome description focuses on adverse events and serious adverse events, with rates adjusted for exposure time. It specifies an analysis period beginning at baseline in the predecessor study and ending at Week 104, with an exclusion for data after the first dose of tezepelumab among participants who switched from placebo.

The safety question is therefore distinct from asking whether asthma symptoms or exacerbations improved. The registry record identifies the treatments, population, and safety endpoint, but does not report the exposure-adjusted rate estimates, uncertainty intervals, or a statistical test comparing treatment groups. The posted adverse-event counts can describe how many participants were affected in the listed groups; they do not, on their own, answer a treatment-effect question.

3. Trial Design

DESTINATION is described as a multicentre, double-blind, randomized, placebo-controlled, parallel-group Phase 3 safety extension study. The registry lists triple masking. The stated purpose is to evaluate the safety and tolerability of tezepelumab in adults and adolescents with severe, uncontrolled asthma. AstraZeneca is the sponsor, and the record lists the study as completed.

The study enrolled 951 participants. Its start date is 2019-01-07, and its primary completion date is 2021-10-26. The brief description says that participants who completed either D5180C00007 or D5180C00009 could be offered the opportunity to consent to the extension. The record describes a treatment phase followed by a follow-up phase in which participants would not receive investigational product. The length of follow-up depended on which predecessor study a participant had completed.

The listed interventions are tezepelumab and placebo, each administered by subcutaneous injection. The adverse-event summaries distinguish groups associated with NAVIGATOR and SOURCE, and identify whether participants were in a tezepelumab, placebo, or placebo-to-tezepelumab group. These labels preserve important context: the displayed groups are not simply interchangeable labels for participants newly randomized within a single, uniform treatment history. The registry record does not provide enough detail to describe all treatment sequences or the allocation process for every extension participant.

The primary outcome is an exposure-adjusted incidence rate of adverse events and serious adverse events. Its stated timeframe runs from baseline, defined as Week 0 in the predecessor study, to Week 104. For participants switching from placebo in the predecessor study to tezepelumab in DESTINATION, data collected after the first dose of tezepelumab are excluded from this analysis. The endpoint description also specifies limits on the period in which events are counted. These details matter because the extension includes participants with different predecessor-study histories and because time at risk may differ across participants.

The record identifies three outcome measures and two analyses, but the detailed statistical plan, allocation ratio, and specific masking roles are not reported in the registry record. The record also does not describe the sample-size justification or interim analyses. Those omissions prevent a fuller reconstruction of how the study was planned and how all analyses were conducted.

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 1209 patients randomized and dosed in predecessor studies, 951 were randomised in DESTINATION and 950 received treatment. The patients receiving tezepelumab in the predecessors continued to receive tezepelumab, while patients receiving placebo in the predecessors were re-randomized 1:1 to either receive tezepelumab in DESTINATION or to continue placebo, resulting in a 3:1 randomization ratio in DESTINATION.

Predecessor Study

Reasons for not completing this period:

Long Term Extension (DESTINATION)

Reasons for not completing this period:

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 Exposure Adjusted Incidence Rates of AEs/SAEs, measured over Baseline (Week 0 in predecessor study) to Week 104. For subjects switching treatments from placebo in the predecessor to tezepelumab in DESTINATION, all data collected after first dose of tezepelumab are excluded..

The primary endpoint is titled “Exposure Adjusted Incidence Rates of AEs/SAEs” and uses the unit patients with adverse events per 100 person-years. The registry defines an exposure-adjusted rate as the number of subjects with adverse events divided by total time at risk across all subjects, multiplied by 100. The analysis is based on the Safety Analysis Set.

This endpoint measures the frequency of participants experiencing events in relation to the amount of time they were observed at risk. In general, an exposure-adjusted rate can be useful when participants contribute different amounts of observation time: a count alone does not show whether the groups were observed for comparable durations. The rate places event experience on a common time-exposure scale. That is a general explanation of the measure, not a claim about the numerical results in this study.

The event-counting window is specifically defined. Events are included if their onset falls between the first dose of investigational product in the predecessor study and the earliest of the last dose plus 33 days, death, study withdrawal, or the day before another biologic is started. The stated overall timeframe is baseline, or Week 0 in the predecessor study, to Week 104. For participants who switched from placebo to tezepelumab in DESTINATION, the primary analysis excludes data collected after their first tezepelumab dose.

The registry record does not report the numerical exposure-adjusted rates or confidence intervals. The endpoint definition therefore explains what was intended to be measured, but the record does not supply the rate estimates needed to assess their magnitude or precision.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The primary outcome uses an exposure-adjusted incidence rate. In general, a rate is a count of events or affected participants considered in relation to the amount of time during which those events could be observed. Here, the registry defines the numerator as the number of subjects with adverse events and the denominator as total time at risk across all subjects, with the result multiplied by 100. The unit is patients with adverse events per 100 person-years. This is a rate measure, not a percentage of participants and not a time-to-first-event measure as described in the registry.

Why adjust for exposure time?

In general, participants may contribute unequal observation time. If one group is observed longer, it may have more opportunities for events to be recorded even when the underlying event rate is similar. An exposure-adjusted rate accounts for the accumulated time at risk rather than comparing counts alone. This adjustment does not automatically make groups comparable: study histories, treatment timing, event definitions, and other sources of difference may still matter. The registry record does not report group-level person-time values, so the rates cannot be independently reconstructed from the counts listed.

What is the event window?

The registry defines eligible adverse events by onset date. The window begins with the first dose of investigational product in the predecessor study and ends at the earliest of the last dose plus 33 days, death, study withdrawal, or the day before starting another biologic. The overall endpoint timeframe is baseline, specified as Week 0 in the predecessor study, to Week 104. For participants switching from placebo in the predecessor study to tezepelumab in DESTINATION, data after the first dose of tezepelumab are excluded. These rules determine which events and exposure time contribute to the endpoint; they are not interchangeable with simply counting every event recorded during follow-up.

What does the Safety Analysis Set mean?

The registry states that the primary analysis is based on the Safety Analysis Set. In general, safety analyses use a population defined for evaluating treatment exposure and safety events, but the exact membership rules for this set are not reported in the registry record. The record therefore supports naming the analysis population, but not describing its detailed inclusion or exclusion criteria. The displayed at-risk counts are group-specific counts and should not be assumed to reveal every rule used to define the analysis set.

How should the group counts be read?

The adverse-event summaries give the number at risk and the number affected for serious and other adverse events in each listed group. Counts answer how many participants were recorded as affected; they do not account for differences in observation time. The groups also carry distinct predecessor-study and treatment-history labels. In general, a comparison of counts across groups can be misleading when exposure duration or participant history differs. For a rate comparison, the exposure denominators and the analysis method would be needed alongside the event counts.

The registry record does not report confidence intervals, standard errors, or hypothesis-test results for the primary outcome. A confidence interval, in general, expresses uncertainty around an estimate under the statistical method used; it helps readers distinguish an estimate’s apparent size from how precisely it is known. Without interval estimates, the precision of the study’s exposure-adjusted rates cannot be assessed from this record. A p-value or a stated testing procedure is also not reported, so no inferential conclusion about a difference between groups can be drawn from the information recorded.

What can a planning illustration establish?

Any sample-size calculation based on an observed effect is a planning illustration, not observed power and not a description of the trial’s original design. The stated illustration assumptions use 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. Such calculations are conditional on their assumptions and do not replace a report of the trial’s own sample-size justification. That justification is not reported in the registry record. No planning sample-size values are discussed in this explanation.

More broadly, an analysis plan would specify how the primary outcome is estimated, how groups are compared, how uncertainty is quantified, and how deviations from the planned analysis are handled. Those details are not reported in the registry record. The stated endpoint definition is useful for understanding the intended measure, but it is not a complete statistical analysis plan.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists three outcome measures and two analyses. It identifies Annualized Asthma Exacerbation Rate as a secondary outcome and describes exposure-adjusted adverse-event and serious-adverse-event rates as the primary outcome. However, the registry record does not report a multiplicity strategy, such as a prespecified order for testing outcomes or an adjustment for examining multiple endpoints. Without that information, the effect of multiple statistical tests on the interpretation of any inferential results cannot be assessed. Numerical test results are not reported in the registry record in any case.

Missing-data procedures are not reported in the registry record. The description specifies an event window and says the analysis is based on the Safety Analysis Set, but does not explain how incomplete observation, withdrawal, or unavailable event information was handled statistically. It also does not give a detailed definition of the Safety Analysis Set. The endpoint’s censoring limits include death, withdrawal, the time after the last dose, and initiation of another biologic; the record does not describe any further modeling or sensitivity analyses related to these limits.

The registry record does not report interim analyses, stopping rules, or a detailed statistical analysis plan. It also does not state whether the primary safety rates were formally compared between groups. These omissions do not show that such procedures were absent; they mean they are not reported in the registry record. The reader can identify the listed outcome and analysis population, but cannot reconstruct the full approach to multiplicity, missing data, or inferential testing.

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 3% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: asthma (10.5%), covid-19 pneumonia (4.1%), encephalocele (3.1%), gastrointestinal haemorrhage (3.1%), pneumonia haemophilus (3.1%).

The serious adverse-event figures are counts of affected participants within the listed groups, alongside the number at risk. For example, NAVIGATOR Rand Teze lists 82 participants with serious adverse events among 528 at risk, while NAVIGATOR Rand Pbo lists 94 among 531 at risk. The SOURCE groups and the placebo-to-tezepelumab switch groups have their own counts. These figures are not exposure-adjusted rates, even though the primary endpoint is defined as a rate per 100 person-years.

In general, the number of affected participants does not show how long each group was observed. It also does not establish that treatment caused an event. The group labels distinguish predecessor studies and treatment histories, so raw differences between counts cannot be read as a controlled treatment effect without further analysis. The registry record does not report the exposure-adjusted estimates or confidence intervals needed to assess their magnitude and precision.

The record lists deaths separately for each group. Those numbers should be read as deaths recorded in the group summaries, not as evidence of treatment causation. Serious adverse-event terms are also listed with percentages, including Asthma at 10.5% and Covid-19 pneumonia at 4.1%. The registry information does not specify the denominator for those term percentages in the record used for this analysis. The event counts, listed terms, and death counts describe safety observations; they do not independently establish comparative risk.

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

The registry record establishes that DESTINATION was designed as a safety extension study in adults and adolescents with severe, uncontrolled asthma, after completion of either D5180C00007 or D5180C00009. It identifies tezepelumab and placebo as the interventions and describes an exposure-adjusted adverse-event endpoint. The record also provides participant counts for serious and other adverse events across groups identified by predecessor study and treatment history.

Those details do not establish whether tezepelumab increased, reduced, or left unchanged the risk of an adverse event. The numerical exposure-adjusted rates, uncertainty intervals, and treatment-group tests are not reported in the registry record. The raw counts alone cannot answer that question because they do not include the total time at risk used in the primary endpoint definition. The groups also have different predecessor-study and treatment-history labels, which makes a simple count comparison an inadequate basis for causal interpretation.

The serious adverse-event terms and recorded deaths are also descriptive. A listed event is not by itself evidence that the study treatment caused it. Likewise, the presence of a serious adverse event in a group does not by itself establish a comparative safety difference. The record’s event-window rules specify what is counted for the primary outcome, but the numerical results needed to evaluate that endpoint are not reported in the registry record.

The record lists Annualized Asthma Exacerbation Rate as a secondary outcome, but its numerical findings are not reported in the registry record. Thus, the available information cannot establish an effect on asthma exacerbations or other clinical outcomes. This distinction is important: a trial’s objective and outcome definitions describe what investigators set out to assess, whereas conclusions about the size and uncertainty of an observed effect require the outcome estimates and their analysis.

Any sample-size figures based on the observed effect are planning illustrations, not observed power and not evidence of the certainty of the study’s findings. The trial’s own sample-size justification is not reported in the registry record. Overall, the record supplies context and descriptive safety counts, but not the inferential results necessary to quantify or compare treatment effects.

13. Why This Trial Matters Statistically

This trial is statistically notable because its primary safety outcome is exposure-adjusted. In an extension study, participants may contribute differing amounts of time under observation, and a count of affected participants alone does not represent the rate per person-time. The registry explicitly defines the numerator, denominator, time window, and unit for the primary endpoint. These details allow readers to understand the intended estimand even though the numerical rate results are not reported in the registry record.

The record also illustrates why treatment history matters when interpreting an extension study. The adverse-event summaries separate NAVIGATOR and SOURCE groups and distinguish participants associated with tezepelumab, placebo, and placebo-to-tezepelumab switching. Those labels show that the summaries span different predecessor-study and treatment histories. In general, group counts are not a substitute for an analysis that accounts for exposure and study context.

There is also an important distinction between safety description and comparative inference. The record lists counts of participants with serious and other adverse events, deaths, and selected serious-event terms. These are meaningful descriptive elements, but the record does not report the exposure-adjusted estimates, confidence intervals, or tests needed to quantify comparative uncertainty. The available information therefore supports careful description, not a definitive statistical comparison.

The record gives a defined endpoint and a named Safety Analysis Set, but it does not report several elements that would help readers audit the analysis: detailed population rules, missing-data handling, multiplicity procedures, interim analyses, or the full statistical plan. Recognizing these boundaries is part of sound statistical interpretation. A well-defined endpoint can clarify what was intended to be measured, while incomplete reporting limits what can be concluded about the results.

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 main limitation for interpreting this record is that the numerical primary endpoint estimates are not reported in the registry record. Although the endpoint is defined as an exposure-adjusted rate, group-level person-time and the calculated rate values are not available in the information. Confidence intervals and statistical comparisons are also not reported. The listed counts therefore cannot be used to assess the primary endpoint’s precision or to establish a treatment-group difference.

The adverse-event summaries cover groups with different labels for predecessor study and treatment history. Some are designated as placebo-to-tezepelumab groups, while others are listed as randomized tezepelumab or placebo groups. The record does not provide enough detail to describe all treatment exposure histories or establish the comparability of these groups. Comparing their unadjusted counts could therefore conflate treatment experience with differences in study context or observation time.

The selected serious-event terms are accompanied by percentages, but the denominator for those percentages is not reported in the registry record. The record also lists death counts without a treatment-causality assessment in the information described. These limitations mean the terms and deaths should remain descriptive rather than be used to infer comparative risk or causation.

Further limitations concern reporting of the analysis. Detailed definitions for the Safety Analysis Set, missing-data procedures, multiplicity handling, interim analyses, and the complete statistical analysis plan are not reported in the registry record. The sample-size justification is also not reported. The study is described as completed, but that status does not provide the missing statistical details or numerical outcome estimates. These gaps restrict independent assessment of the analysis and the strength of any comparative interpretation.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Extension Study to Evaluate the Safety and Tolerability of Tezepelumab in Adults and Adolescents With Severe, Uncontrolled Asthma — NCT03706079.
• Registry record last updated 2023-06-06; status last verified 2023-05.
• Results first posted 2023-02-09.
• 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

NCT03706079 is the completed Phase 3 DESTINATION safety extension study of tezepelumab in adults and adolescents with severe, uncontrolled asthma. The randomized, triple-masked, parallel-group study enrolled 951 participants who had completed D5180C00007 or D5180C00009 and were offered the opportunity to consent. It included subcutaneous tezepelumab and placebo, followed by a period without investigational product; follow-up length depended on the predecessor study.

The primary endpoint is exposure-adjusted incidence rates of adverse events and serious adverse events, expressed as patients with events per 100 person-years. The registry provides group-level counts for serious and other adverse events, along with deaths and selected serious-event terms. It does not report the numerical exposure-adjusted rates, confidence intervals, or treatment-group tests. Annualized Asthma Exacerbation Rate is listed as a secondary outcome, but its numerical findings are not reported in the registry record. The detailed statistical plan, missing-data approach, and multiplicity procedures are also not reported in the registry record.