A Study to Evaluate the Long-Term Safety and Efficacy of Bimekizumab in Subjects With Psoriatic Arthritis: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for A Study to Evaluate the Long-Term Safety and Efficacy of Bimekizumab in Subjects With Psoriatic Arthritis (NCT03347110), a na phase 2 study. The primary outcome is Percentage of Participants With Treatment-emergent Adverse Events (TEAEs) During the Study.

2. Clinical Question

3. Trial Design

This is a phase 2, multicenter, open-label follow-up study of bimekizumab in participants with psoriatic arthritis. The study is listed as completed. Its start date was 2017-11-22, and its primary completion date was 2020-10-29. The sponsor is UCB Biopharma SRL. The registry lists enrollment of 184 participants.

The design is single-group: participants received bimekizumab, with no concurrent control group described. Allocation is listed as not applicable, and masking as none. These features mean that the study was not designed as a blinded, randomized comparison between treatments. The arm description says participants would receive bimekizumab for up to 2 years.

The primary safety observation period began at the PA0009 entry visit and continued until the safety follow-up visit, up to Week 120. The primary outcome concerns treatment-emergent adverse events during that period. The registry defines these events by timing after the start of study medication in PA0009, not by a determination that the medication caused them.

The secondary outcomes include withdrawal due to treatment-emergent adverse events and response measures assessed at Week 48. The listed response measures include ACR20, ACR50, ACR70, PASI75, and PASI90; the record also lists changes in MASES and LDI. These outcomes are calculated relative to baseline of PA0008. That reference is an earlier baseline, not a concurrent comparator within this follow-up study. The registry record does not report the detailed statistical plan, the method used to analyze these outcomes, or the results of those analyses.

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: Participant Flow refers to the Safety Set. Participants who completed the study PA0008 (NCT02969525) were eligible to enroll in study PA0009. A total of 184 participants from PA0008 signed the Informed Consent Form and were enrolled in PA0009 study. Among 184 participants, 1 participant did not receive treatment and was not included in analysis.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: The Safety Set (SS) consisted of all study participants who had given informed consent for PA0009 and had received at least one dose of study medication in PA0009.

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: Baseline Characteristics refer to SS which consisted of all study participants who had given informed consent for PA0009 and had received at least one dose of study medication in PA0009.

6. Primary Endpoint

The registry lists the primary outcome as Percentage of Participants With Treatment-emergent Adverse Events (TEAEs) During the Study, measured over From Entry Visit of PA0009 until Safety Follow-Up Visit (up to Week 120).

The primary endpoint is the percentage of participants with treatment-emergent adverse events during the study. The registry defines an adverse event as an untoward medical occurrence in a participant who has received a pharmaceutical product. An event does not need to have a causal relationship with the treatment. Treatment-emergent adverse events are defined by their timing: they began on or after the start date of study medication in PA0009.

This endpoint is used to describe the occurrence of adverse events during exposure and follow-up. It is a safety measure, not a measure of treatment benefit. Because the definition is based on timing rather than causation, an event counted as treatment-emergent cannot, from this definition alone, be attributed to bimekizumab. The endpoint also compresses a broad range of events into a participant-level percentage; it does not, by itself, convey each event’s severity, duration, or clinical context.

The population specified for the endpoint is the Safety Set: participants who gave informed consent for PA0009 and received at least one dose of study medication in PA0009. The observation window extends from the PA0009 entry visit to the safety follow-up visit, up to Week 120. Although the endpoint is defined, its overall percentage is not reported in the registry record. The posted safety information does list counts for serious and other adverse-event categories, but those counts should not be mistaken for the missing primary endpoint estimate.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The primary outcome is a binary participant-level measure: each participant either had at least one event meeting the treatment-emergent definition during the observation period or did not. A percentage for such an outcome summarizes the number of participants with the event relative to the specified analysis population. The Safety Set definition is explicit: participants had to give informed consent for PA0009 and receive at least one dose of study medication in PA0009. The registry does not report the primary endpoint percentage or the analysis details needed to evaluate how it was estimated.

The distinction between a participant-level measure and a count of events matters. A participant-level percentage describes how many people experienced an event, not the total number of events. A person may experience more than one event, but the registry’s primary endpoint is expressed as a percentage of participants. The adverse-event summary separately reports affected participants in serious and other categories. It should not be assumed that either category is equivalent to the full primary endpoint, which covers treatment-emergent adverse events generally.

The definition of treatment-emergent is temporal. Events qualify if their onset is on or after the start date of study medication in PA0009. The definition of an adverse event does not require a causal relationship with treatment. In general, event timing is useful for describing events arising during a treatment period, while causal attribution requires further assessment. The registry record does not report how causality was assessed, how events were coded, or what rules were used to classify severity beyond the serious-event summary.

General statistical explanation: an estimated percentage is subject to sampling variability because another group of participants could produce a different estimate. A confidence interval communicates that uncertainty under specified assumptions. Its width is affected by the amount of information and by the frequency of the event. Rare events can be particularly difficult to estimate precisely, even when a percentage is reported. Here, no interval estimates for the posted adverse-event counts or outcome measures are reported in the registry record, so their statistical precision cannot be described.

General statistical explanation: a single-group study can describe outcomes observed during follow-up, but it does not provide a contemporaneous untreated or alternative-treatment group for comparison. Changes from a prior baseline may be informative descriptively, but they can also reflect time, differences between study periods, or other factors. The secondary efficacy outcomes are defined relative to baseline of PA0008, while the intervention and primary safety observation belong to PA0009. The registry record does not report a method for adjusting comparisons across these study periods.

The secondary outcomes span different measurement types. ACR20, ACR50, ACR70, PASI75, and PASI90 are listed as percentages of participants meeting response thresholds. MASES and LDI are listed as changes from baseline. General statistical methods for binary outcomes may estimate a response proportion; methods for change outcomes may summarize differences from a baseline measurement. However, the specific estimators, models, handling of repeated measurements, and uncertainty calculations used for these outcomes are not reported in the registry record. No specific model should be inferred from the outcome names alone.

The record identifies 10 outcome measures and 0 analyses. It therefore does not provide analysis results from which effect sizes, confidence intervals, or p-values can be interpreted. The record also does not state whether any interim analyses were planned or conducted, or describe a protocol-based statistical analysis plan. Those details are not reported in the registry record.

The sample-size illustration is described as a planning exercise based on an observed effect, with a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. It describes effects as fractions of the observed effect. These are planning assumptions, not evidence that the trial used that design: the study itself is single-group. The illustration is not observed power and does not establish the probability that the trial detected an effect. The registry record does not report a trial-specific sample-size justification, nor does it report the numerical planning results in the registry record for this analysis.

General explanation: over-dispersion occurs when observed variation exceeds what a statistical model expects. It can make standard errors too small if a model assumes less variation than the data contain. The registry record does not identify an over-dispersion issue or a model for which it was assessed, so this is a general consideration rather than a claim about this study’s analysis.

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("Bimekizumab 160 mg (SS)")
n      <- c(183)
events <- c(148)
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  Bimekizumab 160 mg (SS)  183  148  80.9  74.4  86.3  74.6  85.9  74.6  85.9

11. Multiplicity, Missing Data and Analysis Populations

The registry lists multiple outcomes: the primary treatment-emergent adverse-event measure, withdrawal due to treatment-emergent adverse events, and several Week 48 efficacy measures. When many outcomes or repeated tests are examined, the chance of at least one apparently notable result can increase. General statistical approaches may control that risk by defining a hierarchy or adjusting tests, but the approach depends on the prespecified questions and analysis plan.

The registry record does not report whether multiplicity was addressed, whether outcomes were tested in a hierarchy, or whether any adjustment was planned. It also lists 0 analyses, so there are no posted p-values or outcome estimates to interpret in relation to multiplicity. No multiplicity procedure should be assumed.

The record defines the Safety Set for the primary endpoint as participants who consented to PA0009 and received at least one dose of study medication. It does not report the analysis population for the secondary efficacy outcomes. Missing-data methods, reasons for missing outcome assessments, treatment of participants who discontinued, and rules for incomplete follow-up are not reported in the registry record. These omissions matter because analysis populations and missing-data choices can affect both the estimated outcome and its interpretation.

The registry enrollment is 184, while the serious and other adverse-event summaries each list 183 participants at risk. The record does not explain the difference. It should not be interpreted as a particular reason for exclusion or missing follow-up without further information. The posted record also does not establish whether all participants had complete observation through the safety follow-up visit.

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: cholelithiasis (1.1%), foot deformity (1.1%), anal fistula (0.5%), inguinal hernia (0.5%), umbilical hernia (0.5%).

The serious adverse-event summary lists 183 participants at risk and 14 affected in the Bimekizumab 160 mg Safety Set group. The other adverse-event summary lists 183 at risk and 82 affected, and the death count is 0. The record also lists serious adverse-event terms and their percentages: Cholelithiasis and Foot deformity at 1.1% each; Anal fistula, Inguinal hernia, Umbilical hernia, and Chronic sinusitis at 0.5% each.

These categories should be read as descriptive safety information, not as proof that bimekizumab caused the events. The registry’s general adverse-event definition explicitly does not require a causal relationship, and the treatment-emergent definition is based on when events began. The listed terms are not a complete account of every event’s course, severity, or relationship to treatment. The registry record does not provide additional context for these terms in the registry record for this analysis.

The serious-event counts are not interchangeable with the primary endpoint. The primary endpoint covers treatment-emergent adverse events, whereas the summary distinguishes serious events and other events. The overall primary endpoint percentage is not reported in the registry record. No comparison group is listed, so these safety counts cannot be contrasted with a concurrent control group in this study.

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

The record establishes that a phase 2, open-label, single-group follow-up study of bimekizumab in psoriatic arthritis was completed, with enrollment listed as 184. It defines a primary safety outcome based on treatment-emergent adverse events and gives a safety observation window extending from the PA0009 entry visit to the safety follow-up visit, up to Week 120. It also lists secondary safety and efficacy outcomes, including response and change measures assessed at Week 48 relative to PA0008 baseline.

The posted information does not establish the overall percentage of participants with treatment-emergent adverse events, because that primary estimate is not reported in the registry record. It also does not provide analysis estimates for the listed efficacy outcomes. The adverse-event counts and serious-event terms are useful descriptive information, but they cannot substitute for the missing primary endpoint result or convey the full pattern of events and their uncertainty.

The single-group design means that observed outcomes cannot be interpreted as a direct randomized comparison with another treatment or with no treatment. Open-label conduct also means masking was absent. These design features do not erase the descriptive value of follow-up observations, but they limit what can be concluded about comparative effects and causal attribution. The event definition itself includes occurrences that may not be related to the study medication.

General statistical explanation: a result’s interpretation depends on both its estimate and the uncertainty around it, as well as on the design and analysis population. A numerical estimate without suitable context may be misleading; no estimate at all cannot support a conclusion about magnitude or precision. The registry record does not report confidence intervals, p-values, or analysis details for the outcomes. Accordingly, the posted information supports description of the study design and selected safety counts, not a conclusion about the size or certainty of treatment effects.

The record also does not report a trial-specific sample-size justification, details of missing-data handling, or a multiplicity strategy. These gaps further limit assessment of how the study was planned and how robust any outcome analysis would be. Such details are not reported in the registry record and should not be inferred from the study’s enrollment or outcome list.

14. Why This Trial Matters Statistically

This study is statistically notable as a long-term, single-group follow-up rather than a randomized treatment comparison. Its focus is to describe safety and tolerability during bimekizumab exposure in participants with psoriatic arthritis, with additional outcomes relating to disease response. Recognizing the design is essential: descriptive follow-up data answer different questions from a controlled comparison.

The distinction between temporal association and causation is central to interpreting the primary outcome. The registry defines treatment-emergent adverse events by onset after study medication began, while its adverse-event definition allows events without a causal relationship to treatment. This supports a systematic description of events arising during the observation period, but does not by itself identify which events were caused by the medication.

The follow-up window is also relevant. Safety observation ran from the PA0009 entry visit through the safety follow-up visit, up to Week 120, and the arm description states treatment for up to 2 years. Longer observation can capture events over an extended period, but interpreting the record still requires the number of participants actually followed, the completeness of follow-up, and the analysis results. The record provides selected safety counts but does not report the primary endpoint estimate or details of missingness.

The secondary outcomes illustrate that clinical studies may combine binary response measures with changes in continuous or index-based measures. These outcomes have different statistical interpretations and generally require outcome-specific methods. The registry lists ACR20, ACR50, ACR70, PASI75, PASI90, MASES, and LDI outcomes relative to PA0008 baseline, but does not report their estimates or analysis methods.

For biostatisticians and clinical researchers, this record demonstrates why design, endpoint definition, analysis population, and reporting completeness must be considered together. The posted counts can be described, while the absent estimates and uncertainty measures cannot be reconstructed from the record. The sample-size assumptions described for a planning illustration also should not be confused with the single-group design actually listed.

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 interpreting outcomes is that the registry record lists 0 analyses. It defines the primary endpoint and names secondary outcomes, but does not report estimates for them. Without those results, the magnitude and precision of the outcomes cannot be evaluated. Confidence intervals and p-values are also not reported in the registry record.

The study is open-label and single-group, with no concurrent control group. This restricts comparative interpretation and makes it difficult to distinguish events associated with the treatment period from events that might have occurred for other reasons. The treatment-emergent definition is based on event timing and does not establish causation.

The registry lists enrollment of 184, while the adverse-event summaries list 183 participants at risk. The reason for this difference is not reported in the registry record. The available information does not describe completeness of follow-up, discontinuations beyond the named secondary outcome, or how missing data were handled. It also does not specify the analysis population for the efficacy outcomes.

Although the secondary outcomes are defined relative to baseline of PA0008, the registry record does not describe the statistical approach for comparing those measurements with follow-up outcomes in PA0009. Nor does it report how multiplicity was handled across the outcome list. A trial-specific sample-size justification, interim-analysis information, and detailed analysis plan are not reported in the registry record. These limitations prevent a full assessment of the planned and executed statistical analyses.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: A Study to Evaluate the Long-Term Safety and Efficacy of Bimekizumab in Subjects With Psoriatic Arthritis — NCT03347110.
• Registry record last updated 2023-12-01; status last verified 2023-11.
• Results first posted 2023-12-01.
• 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

NCT03347110 is a completed phase 2, multicenter, open-label, single-group follow-up study of bimekizumab in participants with psoriatic arthritis. The record lists UCB Biopharma SRL as sponsor, enrollment of 184, a start date of 2017-11-22, and a primary completion date of 2020-10-29. Participants were to receive bimekizumab for up to 2 years.

The primary outcome is the percentage of participants with treatment-emergent adverse events from the PA0009 entry visit to the safety follow-up visit, up to Week 120. The Safety Set includes participants who consented and received at least one dose. Secondary outcomes include withdrawal due to treatment-emergent adverse events and Week 48 response or change measures relative to PA0008 baseline.

The adverse-event summary lists 183 participants at risk, 14 affected by serious adverse events, 82 affected in the other adverse-event category, and 0 deaths. The overall primary endpoint estimate and analyses of the listed outcomes are not reported in the registry record.