Efficacy and Safety Study of Secukinumab in Chinese Participants With Non-radiographic Axial Spondyloarthritis: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Efficacy and Safety Study of Secukinumab in Chinese Participants With Non-radiographic Axial Spondyloarthritis (NCT04732117), a randomized phase 3 study. The primary outcome is Assessment of SpondyloArthritis International Society 40 (ASAS40) Response Rate in TNF-alpha-inhibitor-naive Participants at Week 16.

2. Clinical Question

The registry record describes a study of efficacy, safety, and tolerability in Chinese participants with active non-radiographic axial spondyloarthritis. Its primary endpoint focuses on response at Week 16, while the official study title also describes assessment of safety and tolerability up to Week 52. The primary question is therefore time-specific: it compares the response proportions at Week 16, using the endpoint definition and population recorded for that analysis. It does not by itself answer whether outcomes remain different after the placebo group begins open-label treatment, nor does it establish how results would generalize to populations outside the recorded study population.

3. Trial Design

This was a randomized, parallel-group, phase III study described as double-blind and placebo-controlled in its official title. The registry record lists quadruple masking, multicenter conduct, and an enrollment of 137. The condition was non-radiographic axial spondyloarthritis. The record marks the study completed; the recorded study start was 2021-07-21 and primary completion was 2024-04-03.

Participants were assigned to secukinumab or placebo. The secukinumab arm description specifies secukinumab 150 mg in a pre-filled syringe and says treatment was double-blinded until Week 12. It describes open-label secukinumab 150 mg from Week 16, with non-responders at Week 24 escalated to secukinumab 300 mg. The placebo arm description says participants initially received placebo in a pre-filled syringe in a double-blinded manner until Week 12, then switched to open-label secukinumab 150 mg at Week 16. It also describes the Week 24 escalation rule. The registry record’s arm descriptions do not give a complete account of every treatment detail, so details beyond those stated are not reported in the registry record.

The primary efficacy endpoint was assessed at Week 16. The treatment change described from Week 16 is important when interpreting follow-up: the randomized placebo comparison is most directly represented by the Week 16 endpoint, rather than by later outcomes after both arms received open-label secukinumab. The primary population was TNF-alpha-inhibitor-naive participants at baseline who were randomized and assigned study treatment. The primary analysis included 61 participants in the secukinumab arm and 62 in the placebo arm. The all-participant ASAS40 secondary analysis included 68 and 69 participants, respectively. These analysis groups are endpoint-specific; they should not be conflated with the overall enrollment.

The registry record does not report the original sample-size justification or the full operational details of randomization and masking. It also does not report the complete statistical analysis plan. The available record supports describing the design as randomized, parallel, phase III, multicenter, and placebo-controlled, but not filling in protocol details that are not recorded.

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: A screening period of up to 10 weeks before randomization assessed participant eligibility

Double-Blind period (up to Week 16)

Reasons for not completing this period:

Open-label period

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: All randomized participants to whom study treatment was assigned and who were TNF-alpha-naive at baseline

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 Assessment of SpondyloArthritis International Society 40 (ASAS40) Response Rate in TNF-alpha-inhibitor-naive Participants at Week 16, measured over Baseline, Week 16.

The primary endpoint was the percentage of TNF-alpha-inhibitor-naive participants who achieved an Assessment of SpondyloArthritis International Society 40 (ASAS40) response at Week 16. The record defines response as relative improvement of at least 40% and absolute improvement of at least 2 units on a 0 to 10 scale in at least 3 of the 4 main ASAS domains, with no worsening in the remaining domain.

The four domains are the participant’s global assessment of disease activity, back pain, function measured with the Bath Ankylosing Spondylitis Functional Index (BASFI), and inflammation measured as the mean of two Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) questions about morning stiffness. Each domain’s stated scale runs from 0 to 10, with the direction described in the endpoint definition. The response rule combines relative and absolute improvement and also requires that the remaining domain not worsen. It is therefore a threshold-based composite: participants either meet the defined response criteria or do not.

Such a composite is used to capture improvement across several clinically relevant domains rather than relying on a single measurement. A participant must satisfy the specified pattern across domains, so the endpoint is not interchangeable with an average score change. Its meaning depends on the stated thresholds, the domains included, the Week 16 assessment, and the defined analysis population. Discontinued participants and participants with missing responses were classified as non-responders for this endpoint, according to the record.

7. Results Posted in the Registry

• Secukinumab: 59.0% (36/61) versus 25.8% (16/62) on control; risk difference 33.2 percentage points (95% CI 16.7 to 49.7), risk ratio 2.29 (1.43–3.66); unadjusted two-proportion z-test p = <0.001.

8. Secondary Efficacy Endpoints

The registry also posts results for secondary outcomes. For each outcome below, the endpoint type, the test applied to the posted summary statistics, the result and its interpretation are given in turn. Secondary endpoints are usually not adjusted for multiple testing, so they support rather than confirm the primary finding.

ASAS40 Response Rate in All Participants at Week 16

• Endpoint type: Binary: the percentage of participants with the event (counts rebuilt from the posted percentages and group sizes).
• Test: Unadjusted two-proportion z-test, with a Wald 95% confidence interval for the risk difference.
• Result:
  • Secukinumab: 60.3% (41/68) versus 24.6% (17/69) on control; risk difference 35.7 percentage points (95% CI 20.2 to 51.1), risk ratio 2.45 (1.55–3.86); unadjusted two-proportion z-test p = <0.001.
• Interpretation:
  • The 95% confidence interval excludes no difference, so the proportion with the event is statistically higher for Secukinumab than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.

ASAS 5/6 Response Rate at Week 16.

• Endpoint type: Binary: the percentage of participants with the event (counts rebuilt from the posted percentages and group sizes).
• Test: Unadjusted two-proportion z-test, with a Wald 95% confidence interval for the risk difference.
• Result:
  • Secukinumab: 61.8% (42/68) versus 26.1% (18/69) on control; risk difference 35.7 percentage points (95% CI 20.2 to 51.2), risk ratio 2.37 (1.53–3.67); unadjusted two-proportion z-test p = <0.001.
• Interpretation:
  • The 95% confidence interval excludes no difference, so the proportion with the event is statistically higher for Secukinumab than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.

Change From Baseline in Total Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) Score at Week 16

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard errors.
• Result:
  • Secukinumab: mean -3.70 versus -2.15 on control; difference -1.55 (95% CI -2.21 to -0.89), standardized effect d = -0.80; z-test p = <0.001.
• Interpretation:
  • The 95% confidence interval excludes no difference, so the mean is statistically lower for Secukinumab than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.

The posted secondary outcomes give context beyond the primary TNF-alpha-inhibitor-naive ASAS40 analysis. In the all-participant ASAS40 result and the ASAS 5/6 response result, the response proportions were higher in the secukinumab arm than in the placebo arm at Week 16. The BASDAI change outcome also favored a more negative change in the secukinumab arm, with the reported mean difference of -1.55. These outcomes address related but distinct aspects of response and disease activity, so their direction offers supportive context rather than a replacement for the primary endpoint.

The broad agreement in direction across the posted categorical response outcomes and the BASDAI change is useful when considering whether the primary finding is isolated to one measure. However, endpoints differ in their definitions, scales, analysis populations, and statistical models. A response threshold and a mean score change do not measure the same quantity. Their results should therefore be interpreted on their own terms, without treating them as interchangeable replications of the primary test.

The registry record identifies additional secondary outcome topics, including response, function, inflammation, and imaging measures. Detailed numeric results for all listed outcomes are not reported in the registry record. The available information therefore does not support an inference that every secondary endpoint followed the same pattern.

Multiplicity is another reason to give unadjusted secondary findings less weight. When several outcomes are examined, the chance of at least one apparently unusual result can increase even if none reflects a true difference. The posted secondary comparisons include unadjusted p-values, and a multiplicity adjustment or confirmatory testing hierarchy is not reported in the registry record. These secondary findings are best viewed as complementary evidence that may help frame further study, rather than as a collection of independently definitive conclusions.

The primary result remains the main efficacy estimate because it is designated as the primary endpoint and has a stated population, Week 16 time point, and response definition. The secondary outcomes help describe the breadth of the observed pattern, but they do not broaden the primary analysis population or establish effects beyond the outcomes and time points recorded.

Secondary outcomes registered for this trial, for reference (only those above were recalculated):

• ASAS40 Response Rate in All Participants at Week 16
• ASAS 5/6 Response Rate at Week 16.
• Change From Baseline in Total Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) Score at Week 16
• BASDAI 50 Rate at Week 16
• Change From Baseline of High Sensitivity C-Reactive Protein (hsCRP) at Week 16
• Change From Baseline in Total Bath Ankylosing Spondylitis Functional Index (BASFI) at Week 16
• Change From Baseline in Sacroiliac Joint (SIJ) Edema Score on Magentic Resonance Imaging (MRI) at Week 16
• ASAS20 Response Rate at Week 16

9. Statistical Interpretation

10. Statistical Methods Explained

What does a response proportion represent?

ASAS40 is a binary endpoint: each participant is classified as meeting or not meeting the response definition. The arm-level percentage is the proportion classified as responders among the participants in that endpoint analysis. It does not describe the average degree of improvement among responders, and it does not show how every individual domain changed. The response rule is demanding in the sense that improvement must occur across at least 3 of 4 domains while the remaining domain does not worsen; that is a description of the endpoint definition, not a judgment about treatment.

The record gives the primary arm response estimates as percentages and provides 95% confidence intervals. A confidence interval is an uncertainty range generated by a statistical procedure. In repeated use under the procedure’s assumptions, intervals at this confidence level would cover the corresponding fixed quantity at the stated frequency. For an individual trial, it is best understood as a range of estimates compatible with the data and method, not as a range containing a known true value with a probability attached after the result is observed.

What is the risk difference?

The risk difference compares two response proportions by subtracting one proportion from the other on the proportion scale. The primary comparison reports a risk difference of 0.332 and a 95% confidence interval from 0.168 to 0.497. Positive values indicate a higher response proportion in the secukinumab arm under the comparison’s direction. The interval describes uncertainty about the absolute contrast, and its position relative to zero is relevant to whether the data are compatible with no difference under this method.

Other effect measures, such as risk ratios or odds ratios, express contrasts on different scales. They can be useful for different questions, but they are not interchangeable with an absolute difference. The posted interpretation should prioritize the endpoint rates and the reported risk difference, because those directly convey the observed response proportions and their absolute contrast. No alternative effect measure is needed to establish the basic direction of the reported Week 16 pattern.

How does the model fit into the analysis?

The primary endpoint description states that a logistic regression model was used to assess the percentage of TNF-alpha-inhibitor-naive participants achieving ASAS40 at Week 16. In general, logistic regression models the probability of a binary outcome, such as response versus non-response, using a mathematical relationship that keeps predicted probabilities within their allowable range. A model can include explanatory variables, but the registry record does not state which covariates were included, how they were selected, or what adjusted estimates were reported. Those details are not reported in the registry record.

The posted arm percentages and the reported comparison should not be assumed to describe every detail of that regression model. In particular, the record’s endpoint description names the model, but does not give the model specification, diagnostics, or full output. The comparison also supplies an unadjusted p-value. An unadjusted p-value does not account for testing several outcomes or comparisons, and it should not be interpreted as a multiplicity-adjusted result.

How were missing responses handled?

For the primary endpoint, participants who discontinued and participants with missing responses were considered non-responders. This is a non-responder imputation rule: a missing Week 16 response is classified as failure to meet the response criterion for the endpoint analysis rather than being omitted or filled in using a modeled response value. The rule makes the treatment of missing endpoint data explicit, but it does not show how many participants had missing responses, why responses were missing, or whether alternative missing-data analyses were conducted. Those details are not reported in the registry record.

Missing-data rules can affect binary response proportions, especially if missingness differs between groups or is related to outcome. Classifying missing responses as non-response is one prespecified-style approach, but the record does not provide enough information to assess the consequences of missingness or compare this rule with other approaches. The number of participants in each analysis is endpoint-specific and should be kept distinct from overall enrollment.

Why can over-dispersion matter?

For binary outcomes, a simple statistical model may assume that the observed variation is adequately described by its probability structure and sample size. Over-dispersion, in general, means that observed variability is greater than the model’s assumptions anticipate. If a method ignores meaningful extra variation, standard errors may be too small and intervals may appear too narrow. This is a general statistical consideration, not a reported feature of this trial. The registry record does not report an over-dispersion assessment or a correction for it.

Model assumptions also include how observations are treated and whether the chosen model represents the analysis structure appropriately. Randomization supports the comparison by assigning participants to treatment groups, but it does not remove the need to define the analysis population, outcome, missing-data handling, and statistical model. The available record specifies the primary population, endpoint, response rule, and missing-response classification, while the fuller model specification is not reported.

How should the p-value be read?

The primary unadjusted p-value is <0.001. In general, a p-value is calculated under a null hypothesis and statistical model, and describes the compatibility of the observed data, or more extreme data, with that setup. It does not quantify the probability that treatment has no effect, and it does not measure the clinical relevance of the estimated difference. The confidence interval and response proportions are needed to understand the size and precision of the observed contrast.

The record includes no reported analysis entries for the secondary endpoints. It also does not report a multiplicity procedure. Consequently, secondary p-values in the posted summaries should be treated as unadjusted evidence rather than as a set of confirmatory tests with family-wise error controlled. The registry record does not report the original analysis plan, so the intended hierarchy among secondary outcomes cannot be established from the available information.

Finally, sample-size illustrations based on observed effects answer a different question from the trial’s original design assumptions. They describe planning requirements under stated hypothetical assumptions; they do not reconstruct the study’s actual design rationale or tell how likely this completed trial was to detect an effect. The original sample-size justification is not reported in the registry record.

11. Confidence Intervals and Precision

The primary response proportions have 95% confidence intervals of 46.41% to 71.03% for secukinumab and 15.12% to 36.94% for placebo. These intervals show that the estimated response rates are not known with exact precision. In particular, the plausible range around each arm estimate spans several percentage points, so the point estimate should not be treated as a perfectly precise population value.

The confidence interval for the risk difference, 0.168 to 0.497, gives uncertainty for the absolute comparison. It remains above zero, while still allowing a range of possible magnitudes. Thus the result is more informative than a direction-only statement: it indicates both the direction of the estimated contrast and the uncertainty around its size. The interval does not establish that every value within it is equally likely, nor does it guarantee that the true effect lies within the range in this particular study.

Confidence intervals are affected by the amount of information and by outcome variability. In general, more informative data can produce narrower intervals, while limited information or substantial variability can produce wider ones. The primary analysis groups were 61 participants for secukinumab and 62 for placebo. These are the endpoint analysis denominators, not a statement that every randomized participant contributed a complete observed Week 16 response; the endpoint rule classified discontinued participants and those with missing responses as non-responders.

The record provides confidence intervals for the arm-level primary response estimates and the risk difference. It does not give a complete model specification or all details needed to independently assess the interval method. Precision should therefore be read from the posted intervals while keeping the stated endpoint, analysis population, and missing-response rule in view. The interval supports a positive Week 16 contrast under the reported analysis, but it does not resolve uncertainty about longer-term outcomes or applicability beyond the studied population.

12. Planning a Similar Trial: Sample Size

This is a planning illustration, not a re-evaluation of the original trial. It asks: if a new study wanted to detect a difference like the one observed, or a smaller one, how large would it need to be? It is deliberately not “observed power” of the finished trial, which is not a meaningful quantity.

The sample-size planning figures are illustrative, not a record of the trial’s original design justification. They use a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The effects considered are stated fractions of the observed effect: 100%, 75%, and 50%. For these binary response outcomes, the figures are participants per arm. The note about total events applies to time-to-event outcomes, not these response measures.

The 80% power column gives the number of participants per arm that the planning calculation estimates would be needed for an 80% chance of detecting the specified effect under the stated assumptions, if that effect were the true one and the analysis followed those assumptions. The 90% power column expresses the same planning question using a higher target chance of detection. The calculation is conditional on the assumed effect and statistical setup; it does not guarantee that a future study will achieve that probability or detect an effect.

For the primary endpoint, the planning figures rise as the assumed effect becomes smaller: the calculation uses 34 participants per arm for 80% power and 45 for 90% power at 100% of the observed effect; 59 and 78 when using 75%; and 127 and 170 when using 50%. This pattern is expected because smaller effects are harder to distinguish from sampling variation, so more participants are generally needed to detect them at the same target power.

These calculations are based on the observed effect and are not observed power. They should not be read as a post hoc measure of how successful the completed study was. The original trial’s own sample-size assumptions and justification are not reported in the registry record, so the illustrations cannot establish whether the enrollment was chosen using these assumptions.

13. How the Sample Size Is Derived

Power is the probability that a study of a given size rejects the null hypothesis when a specific true effect exists. It depends on four things: the effect to detect, the variability of the outcome, the significance level (here a two-sided α of 0.05, so z_1−α/2 = 1.960) and the desired power (z_1−β = 0.842 for 80% and 1.282 for 90%).

Formula

n is the number of participants in each arm, p₀ and p₁ are the control and treatment proportions, and p̄ is their average.

Worked calculation for this trial

1. Control proportion p₀ = 0.258; treatment proportion p₁ = 0.590; average p̄ = 0.424.
2. First term: z_1−α/2 × √[2p̄(1−p̄)] = 1.96 × 0.6989 = 1.3698.
3. Second term: z_1−β × √[p₀(1−p₀) + p₁(1−p₁)] = 0.842 × 0.6583 = 0.5540.
4. n = (1.3698 + 0.5540)² / (0.3321)² = 33.6, rounded up to 34 participants per arm for 80% power.

The smaller-effect rows in the table above repeat the same calculation with the effect multiplied by 0.75 and 0.5 (for ratios, applied to the logarithm of the ratio).

R code

alpha <- 0.05
z_a   <- qnorm(1 - alpha / 2)          # two-sided
p0 <- 0.258064516129032                          # control proportion
p1 <- 0.590163934426229                          # treatment proportion
n_per_arm <- function(power, frac = 1) {
  q1 <- p0 + (p1 - p0) * frac               # smaller effect = fraction of the observed difference
  pbar <- (p0 + q1) / 2
  z_b <- qnorm(power)
  ceiling(round((z_a * sqrt(2 * pbar * (1 - pbar)) + z_b * sqrt(p0 * (1 - p0) + q1 * (1 - q1)))^2 / (q1 - p0)^2, 6))
}
for (f in c(1, 0.75, 0.5))
  cat(sprintf("%3.0f%% of observed effect: n per arm = %s (80%% power), %s (90%% power)\n", 100 * f,
              format(n_per_arm(0.80, f), big.mark = ","), format(n_per_arm(0.90, f), big.mark = ",")))

# Check against R's built-in function (unrounded n per arm)
cat("power.prop.test:", round(power.prop.test(p1 = p0, p2 = p1, power = 0.80)$n, 1), "\n")

# Simulation: how often does the z-test reject at the 80%-power sample size?
set.seed(4732117)
n    <- n_per_arm(0.80)
reps <- 20000
x0 <- rbinom(reps, n, p0); x1 <- rbinom(reps, n, p1)
ph <- (x0 + x1) / (2 * n)
z  <- ((x1 - x0) / n) / sqrt(ph * (1 - ph) * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(z) > z_a, na.rm = TRUE), reps))

Output from running the code

100% of observed effect: n per arm = 34 (80% power), 45 (90% power)
 75% of observed effect: n per arm = 59 (80% power), 78 (90% power)
 50% of observed effect: n per arm = 127 (80% power), 170 (90% power)
power.prop.test: 33.6 
Simulated power at n = 34 per arm: 0.810 (20000 replicates)

The simulation draws many pairs of event counts at the planned sample size and counts how often the two-proportion z-test rejects the null. It should land close to the target power; at very small required sample sizes it can fall below it, because the normal approximation is rough there.

14. Multiplicity, Missing Data and Analysis Populations

Multiplicity arises when several endpoints, comparisons, or time points are tested. Even if each test is evaluated using the same nominal threshold, making many tests creates more opportunities for a chance finding. Statistical plans often address this by specifying a testing hierarchy, adjusting significance thresholds, or using another procedure to control error across a family of tests. The registry record does not report a multiplicity adjustment or a hierarchy for the secondary outcomes. The posted secondary p-values are unadjusted and should not be treated as if they controlled the overall chance of a false-positive finding.

The primary endpoint is clearly identified: Week 16 ASAS40 response among TNF-alpha-inhibitor-naive participants. Its description says a logistic regression model was used and identifies the missing-response rule. However, the model’s covariates, full specification, diagnostic approach, and complete statistical plan are not reported in the registry record. The record also does not report interim analyses or a sample-size justification. These omissions limit assessment of how the reported analysis relates to the original planned analysis.

For the primary endpoint, participants who discontinued and those with missing responses were treated as non-responders. This rule retains them in the response classification, but the record does not say how many had missing responses, describe reasons for missingness, or report sensitivity analyses using alternative assumptions. It is not possible from the registry record to judge whether missingness could have altered the estimated contrast.

The primary analysis population excludes participants who were not TNF-alpha-inhibitor-naive at baseline, while a separate secondary ASAS40 analysis concerns all participants. The record supplies endpoint-specific denominators, but does not provide enough detail to reconcile every analysis population with all randomized participants or explain all exclusions. This reinforces the need to interpret each estimate according to its stated population, rather than treating all endpoints as based on the same group.

15. 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: paronychia (3.4%), tonsillitis (3.4%), anal fistula (1.4%), gastritis erosive (0.7%), rib fracture (0.7%).

The safety summaries use different exposure groups and denominators, so they should be read as reported rather than combined into a single treatment comparison. Serious adverse events were reported for 4 of 135 participants in the secukinumab 150 mg group, 2 of 29 in the secukinumab 300 mg group, 6 of 135 in the any-secukinumab group, and 1 of 69 in the placebo group. Deaths were 0 in each listed group.

The record also reports other adverse events for 103 of 135 participants in the 150 mg group, 22 of 29 in the 300 mg group, 114 of 135 in the any-secukinumab group, and 52 of 69 in the placebo group. The treatment descriptions include a switch from placebo to open-label secukinumab and dose escalation, so the exposure group definitions and periods matter. The any-secukinumab group is not an independent arm alongside the dose-specific groups.

Listed serious adverse event terms include paronychia and tonsillitis at 3.4% each, anal fistula at 1.4%, and gastritis erosive, rib fracture, and neuroendocrine tumour of the rectum at 0.7% each. These summaries describe reported events; they do not establish that treatment caused an event or permit a full comparative risk assessment. The registry record does not report additional details needed to interpret event timing or attribution.

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

The primary result describes a Week 16 difference in ASAS40 response proportions between randomized secukinumab and placebo groups in TNF-alpha-inhibitor-naive participants. It supports the conclusion that the posted data show a higher response proportion in the secukinumab arm for this endpoint and time point. The confidence interval for the risk difference is above zero, while its width indicates uncertainty about the precise magnitude.

This result does not mean every participant responded, and it does not describe the size of improvement for each individual. ASAS40 is a threshold-based composite, so it classifies whether a participant met the response rule across the specified domains. It is distinct from a mean change in BASDAI, a functional score change, or an imaging outcome.

The result also does not establish an effect for all people with non-radiographic axial spondyloarthritis. The primary estimate applies to the defined TNF-alpha-inhibitor-naive analysis population in this study of Chinese participants. It does not by itself establish outcomes in other populations, for other treatment histories, or outside the study conditions.

The Week 16 comparison should not be interpreted as a continuing randomized placebo contrast throughout follow-up. The registry record says participants in the placebo arm switched to open-label secukinumab at Week 16. Later observations therefore reflect a treatment sequence in which the original placebo assignment no longer corresponds to continued placebo exposure as described. The primary efficacy finding is specifically tied to Week 16.

Finally, a statistical difference is not the same as a complete assessment of benefit, risk, or clinical importance. The record includes safety summaries and secondary outcomes, but unadjusted secondary comparisons have less evidential weight when multiplicity is not addressed. The result is one piece of trial evidence, with its meaning bounded by the endpoint, population, assessment time, analysis, and registry information available.

17. Why This Trial Matters Statistically

This trial illustrates why a clinical result must be read together with its population and endpoint definition. The primary estimate is not simply “ASAS40 in the trial”; it concerns TNF-alpha-inhibitor-naive randomized participants assigned treatment, assessed at Week 16, under a specified composite response rule. A separate all-participant ASAS40 analysis has different denominators and should not be substituted for the primary result.

It also demonstrates the value of reporting both arm-level response proportions and an absolute contrast with a confidence interval. The proportions describe the observed response in each group, while the risk difference quantifies the contrast on an absolute scale. The interval makes visible that an estimated effect has uncertainty, even when its reported p-value is small.

The treatment sequence is statistically important. A placebo-controlled contrast at Week 16 and subsequent follow-up after switching to open-label treatment answer different questions. Later data cannot be casually interpreted as if placebo exposure continued unchanged. This distinction is central to understanding what randomization can support at each stage of follow-up.

Finally, this record highlights the limits of registry summaries. It identifies the primary endpoint, analysis population, response definition, and missing-response rule, but does not report the full model specification, multiplicity plan, original sample-size justification, or all details for the listed secondary outcomes. Clear reporting of those elements helps readers distinguish a precise, prespecified inference from exploratory or incompletely documented results.

18. 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.
• Participant counts were reconstructed from posted percentages and arm sizes, so small rounding differences are possible.

The primary analysis population is limited to participants who were TNF-alpha-inhibitor-naive at baseline. Although the registry record also reports an all-participant ASAS40 secondary result, the primary estimate should not be generalized automatically beyond its defined population. The study enrolled Chinese participants with active non-radiographic axial spondyloarthritis; generalizability beyond that population is not established by this record.

The primary endpoint is assessed at Week 16. The treatment descriptions state that placebo participants switched to open-label secukinumab from Week 16, which limits interpretation of later follow-up as a continued placebo-controlled comparison. The registry record describes safety and tolerability assessment up to Week 52, but the posted efficacy results do not provide a Week 52 randomized placebo contrast.

The primary endpoint’s missing-data approach classified discontinuations and missing responses as non-responders. The registry record does not report the number or reasons for missing responses, nor does it describe sensitivity analyses. The record also does not provide the full logistic regression specification, covariates, diagnostic information, or complete analysis plan. These omissions constrain independent evaluation of the modeled estimate.

Multiplicity handling for secondary endpoints is not reported, and the available numeric secondary results do not cover every secondary outcome listed in the record. The original sample-size justification and trial design assumptions are also not reported. Safety group denominators differ, reflecting treatment exposure categories and the described treatment changes; the summaries should not be treated as a simple fixed-dose, fixed-period comparison. These are limitations of what can be inferred from the registry record, not evidence that the underlying protocol lacked additional procedures.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Efficacy and Safety Study of Secukinumab in Chinese Participants With Non-radiographic Axial Spondyloarthritis — NCT04732117.
• Registry record last updated 2026-04-09; status last verified 2026-03.
• Results first posted 2026-01-30.
• 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.

22. Record Summary

The registry record describes a completed randomized, parallel-group, multicenter phase III study of subcutaneous secukinumab versus placebo in Chinese participants with active non-radiographic axial spondyloarthritis. It lists quadruple masking and an enrollment of 137. The primary endpoint was Week 16 ASAS40 response in TNF-alpha-inhibitor-naive participants, with discontinued participants and missing responses classified as non-responders.

ASAS40 response was 58.72% with secukinumab and 26.03% with placebo; the reported risk difference was 0.332, with a 95% confidence interval from 0.168 to 0.497 and an unadjusted p-value of <0.001. The endpoint is a composite response measure across specified disease domains. Secondary results include higher response proportions for the posted categorical outcomes and a more negative BASDAI change in the secukinumab arm. These should be interpreted as secondary, unadjusted findings.

The record also reports serious and other adverse event summaries, with no deaths listed in the reported groups. Full model details, multiplicity handling, the original sample-size justification, and complete numeric results for all secondary outcomes are not reported in the registry record.