Efficacy and Safety of Belimumab in Black Race Patients With Systemic Lupus Erythematosus (SLE): Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Efficacy and Safety of Belimumab in Black Race Patients With Systemic Lupus Erythematosus (SLE) (NCT01632241), a randomized phase 4 study. The primary outcome is Percentage of Participants Achieving a Systemic Lupus Erythematosus Responder Index (SRI) Response Rate With the Modified Systemic Lupus Erythematosus Disease Activity Index- 2K (SLEDAI-2K) Scoring for Proteinuria at Week 52 [DB Phase].

2. Clinical Question

3. Trial Design

The registry describes a Phase 4, multicenter, randomized, double-blind, placebo-controlled study with a parallel-group design and quadruple masking. Its official title describes a 52-week study. The listed study condition is systemic lupus erythematosus, and the intended population was adult participants of Black race. Enrollment is recorded as 503. The study is marked completed; the registry record lists a start date of 2013-02-19 and primary completion on 2018-06-18.

The double-blind comparison was belimumab 10 mg/kg plus standard therapy versus placebo plus standard therapy. Both treatments were administered intravenously on Days 0, 14, and 28, then every 28 days through Week 48, with a final double-blind evaluation at Week 52. The record also describes an open-label extension. Participants assigned to placebo who opted to enter it could receive belimumab, while participants who had received belimumab could continue receiving it. Open-label outcomes therefore concern a different treatment setting from the randomized double-blind comparison.

The primary analysis population is described as modified intention-to-treat. It excluded the safety-population participants with assessments at three specified sites. The primary endpoint description also notes that one belimumab-arm participant did not have a screening or baseline PGA assessment and was not included in the SRI or component analysis. The endpoint-specific arm counts should be read as analysis counts for the relevant result, not as a new statement of overall enrollment.

The registry record does not report the original sample-size justification or the trial’s original planning assumptions. It also does not report enough detail to reconstruct every analysis population and every missing-data procedure across all outcomes. The planning illustrations are separate from the trial’s own design information.

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 total of 503 participants were randomized of which 496 received at-least one dose of study medication during double-blinded phase (7 participants were randomized but not treated as they were randomized in error). A total of 359 out of 373 participants who completed double-blinded phase opted to continue optional open-label (OL) extension phase.

Double-blinded (Up to Week 52)

Reasons for not completing this period:

Open-label (Week 52 to Week 76)

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: mITT Population. One participant in the mITT population Belimumab 10 mg/kg arm did not have a screening or Baseline PGA assessment; therefore, this participant did not contribute to the SRI/component analysis.

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 Percentage of Participants Achieving a Systemic Lupus Erythematosus Responder Index (SRI) Response Rate With the Modified Systemic Lupus Erythematosus Disease Activity Index- 2K (SLEDAI-2K) Scoring for Proteinuria at Week 52 [DB Phase], measured over Week 52.

The primary endpoint is the percentage of participants who achieved an SRI response at Week 52 of the double-blind phase. The SRI combines a change in disease activity with criteria intended to identify worsening in other assessments. Response required a reduction of at least 4 points from baseline in the SELENA SLEDAI score, using modified SLEDAI-2K scoring for proteinuria. It also required no worsening in Physician’s Global Assessment, defined as an increase of less than 0.30 points from baseline, and no new BILAG A organ-domain score or two new BILAG B organ-domain scores compared with baseline.

This kind of composite endpoint is used to represent response across more than one disease assessment rather than relying on a single component. A participant had to meet all stated response conditions to count as a responder. The registry record says that drop-outs and treatment failures were counted as non-responders in this analysis. That rule affects how the binary outcome is defined: participants who did not remain in the required assessment pathway were not counted as successful responses under the stated endpoint definition.

The endpoint is a proportion, so its group results describe how often the defined response occurred among participants in each analysis arm. It does not by itself describe the size of a response among responders, the course of every disease feature, or the full balance of benefits and harms. The registry record reports a logistic regression analysis for the comparison, with treatment group and specified baseline and region covariates in the model.

7. Results Posted in the Registry

• Belimumab 10 mg/kg (DB Phase): 48.7% (145/298) versus 41.6% (62/149) on control; risk difference 7.0 percentage points (95% CI -2.7 to 16.8), risk ratio 1.17 (0.94–1.46); unadjusted two-proportion z-test p = 0.159.

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.

Percentage of Participants Achieving SRI-SS Response Rate at Week 52 [DB Phase]

• 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:
  • Belimumab 10 mg/kg (DB Phase): 49.0% (146/298) versus 41.6% (62/149) on control; risk difference 7.4 percentage points (95% CI -2.4 to 17.1), risk ratio 1.18 (0.94–1.47); unadjusted two-proportion z-test p = 0.140.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Belimumab 10 mg/kg (DB Phase) and the control. The interval gives the range of effects that remain compatible with the data.

Percentage of Participants Achieving SRI-SS Response Rate With the SELENA SLEDAI for Scoring of Proteinuria at Week 24 of OL Phase

• 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:
  • Belimumab 10 mg/kg to Belimumab 10 mg/kg (OL Phase): 73.1% (152/208) versus 19.4% (13/67) on control; risk difference 53.7 percentage points (95% CI 42.4 to 64.9), risk ratio 3.77 (2.30–6.18); 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 Belimumab 10 mg/kg to Belimumab 10 mg/kg (OL Phase) than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.

Time to First Severe Flare (as Measured by the Modified SLE Flare Index) up to 52 Weeks [DB Phase]

• Endpoint type: Time to event: compared as a hazard ratio.
• Test: Hazard ratio as reported by the sponsor (Cox proportional hazards model); it was not recalculated.
• Result:
  • Placebo (DB Phase) vs Belimumab 10 mg/kg (DB Phase): hazard ratio 0.77 (95% CI 0.51–1.17), reported p = 0.226 (as reported in the registry).
• Interpretation:
  • The 95% confidence interval includes no difference (a ratio of 1), so these data do not show a statistically significant difference between Placebo (DB Phase) vs Belimumab 10 mg/kg (DB Phase) and the control. The interval gives the range of effects that remain compatible with the data.

The secondary endpoints cover several kinds of outcomes: another Week 52 SRI response definition, an open-label SRI response assessment, time to first severe flare, prednisone-dose reduction outcomes, and adverse-event counts. This range means that the secondary results do not all estimate the same treatment effect or answer the same question. Some are binary proportions, some concern time to an event, and others describe safety or medication use.

The posted double-blind Week 52 SRI-SS response result is directionally similar to the primary endpoint comparison, with a higher response percentage in the belimumab group. The severe-flare analysis is a separate time-to-event result, with a confidence interval that includes the hazard-ratio null. The open-label response assessment compares groups with different treatment histories after the double-blind period; it should not be read as another placebo-controlled randomized comparison. Numerical results for the other listed secondary outcomes are not reported in the registry record.

These findings add context to the primary result but do not convert it into a different or more conclusive result. In particular, outcomes from an open-label period have different interpretive limits from blinded randomized outcomes. A pattern across endpoints can be informative, but endpoints may differ in definition, follow-up, analysis population, and susceptibility to missing observations.

Unadjusted secondary results generally carry less confirmatory weight when many outcomes are examined and no multiplicity procedure is reported. In general, testing multiple outcomes increases the chance that at least one result appears unusual by chance. The registry record does not report a complete multiplicity plan, so the secondary findings are best treated as supportive or exploratory evidence rather than as independent proof. This caution does not erase the observed results; it describes the limits on how strongly they can support a broad conclusion.

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

• Percentage of Participants Achieving SRI-SS Response Rate at Week 52 [DB Phase]
• Percentage of Participants Achieving SRI-SS Response Rate With the SELENA SLEDAI for Scoring of Proteinuria at Week 24 of OL Phase
• Time to First Severe Flare (as Measured by the Modified SLE Flare Index) up to 52 Weeks [DB Phase]
• Time to First Severe Flare (as Measured by the Modified SLE Flare Index) [OL Phase]
• Percent of Participants Whose Average Prednisone Dose Had Been Reduced by >=25% From Baseline to <=7.5 mg/Day During Week 40 Through 52, in Participants Receiving Greater Than 7.5 mg/Day at Baseline [DB Phase]
• Percent of Participants Whose Average Prednisone Dose Had Been Reduced to <=7.5 mg/Day in Participants Receiving Greater Than 7.5 mg/Day at Pre-belimumab Baseline (at Week 28 of OL Phase)
• Number of Participants With nSAEs and SAEs [DB Phase]
• Number of Participants With Severe AEs [DB Phase]

9. Statistical Interpretation

10. Statistical Methods Explained

The primary outcome is binary: each participant is classified as an SRI responder or non-responder under the stated criteria. The reported group percentages describe the frequency of response. A logistic regression model was used for the primary comparison, with treatment group, baseline SELENA SLEDAI score category, baseline complement status, and region listed as covariates. The model reports an odds ratio, which compares the odds of response between groups after accounting for those covariates. Odds are not the same as probabilities, so the odds ratio should not be read as a direct percentage-point difference.

What does an odds ratio describe?

In general, an odds ratio compares the odds of an event in one group with the odds in another. An odds ratio of 1 corresponds to equal odds; values above 1 indicate higher odds in the group named in the comparison, and values below 1 indicate lower odds. The primary reported odds ratio is 1.40. Its 95% confidence interval, 0.93 to 2.11, includes 1, so the interval is compatible with equal odds as well as with effects on either side of that value. The model’s reported p-value is 0.107.

The recalculated risk difference is an unadjusted absolute contrast derived from the posted response counts and analysis denominators. It answers a different descriptive question from the adjusted odds ratio: it compares the proportions directly rather than comparing adjusted odds. Because the two summaries differ in scale and adjustment, their numerical values should not be treated as interchangeable. The recalculation is useful for describing the posted counts, while the registry’s reported regression is the analysis identified by the record.

Why use a regression model?

In general, regression can account for specified covariates while estimating the association between treatment assignment and an outcome. Here, the registry lists baseline disease-activity category, complement status, and region alongside treatment group in the logistic model. Adjustment can help make the treatment comparison conditional on those listed factors. It does not automatically remove bias from unmeasured factors, incorrect model assumptions, or limitations in how participants and outcomes were recorded. The registry record does not provide enough detail to evaluate every model diagnostic or the exact handling of all missing covariate information.

How is the flare outcome different?

The severe-flare outcome is time-to-event: it concerns time until the first severe flare, measured with the modified SLE Flare Index, up to 52 weeks. The registry reports a Cox proportional hazards model and a hazard ratio of 0.77, with a 95% confidence interval from 0.51 to 1.17 and p = 0.226. In general, a hazard ratio compares event rates over follow-up among participants who have not yet had the event, under the model’s assumptions. It is not a comparison of simple event proportions and does not directly state how many days were gained or lost.

Time-to-event analyses can use information about when events occur and can account for participants whose event time is not observed through the full follow-up, under appropriate censoring assumptions. The registry record does not provide the censoring details needed to assess those assumptions. It reports the Cox model and its estimate, but not a full account of model checks or proportional-hazards diagnostics. The arm-level median values are not fully displayed as ordinary numerical medians in the record, so the reported hazard ratio is the clearest available comparative statistic for this endpoint.

What does a confidence interval add?

In general, a confidence interval expresses the uncertainty around an estimated effect under the analysis method. A narrower interval indicates greater precision than a wider interval on the same scale, while the interval’s location indicates which effects remain compatible with the data and model. For a risk difference, zero represents no absolute difference; for an odds ratio or hazard ratio, 1 represents no relative difference. The relevant null value depends on the measure being reported.

A p-value describes how unusual the observed data, or more extreme data, would be under a specified null model and its assumptions. It is not the probability that the null hypothesis is true, and it does not measure clinical importance. The registry’s adjusted p-values and the recalculated unadjusted p-values are not identical analyses. Any interpretation should identify which model and endpoint a given value belongs to rather than treating all p-values as a single test.

What is not specified?

The registry record does not report the complete prespecified statistical analysis plan, the original sample-size calculation, or a full account of interim analyses. It also does not report a comprehensive multiplicity procedure for the endpoint family. Those omissions limit assessment of which comparisons were confirmatory, how type I error was controlled across outcomes, and whether all analysis choices followed a prospectively fixed plan. The record states that primary drop-outs and treatment failures were set to non-responders, but other missing-data details are not reported in the registry record.

11. Confidence Intervals and Precision

Precision concerns how tightly the available data locate an effect estimate. For the primary sponsor-reported odds ratio, the 95% confidence interval is 0.93 to 2.11 around an estimate of 1.40. Because the interval extends below and above 1, it includes the value corresponding to equal odds. The data therefore do not pin down a single direction of association with high precision under this model. The reported p-value, 0.107, is consistent with that interval-based reading at the conventional 0.05 threshold.

The group response percentages, 41.6% and 48.7%, are point estimates. A point estimate gives one summary value from the observed analysis sample, but it does not show the uncertainty by itself. The recalculated unadjusted risk-difference interval crosses zero, so the posted counts are compatible with no absolute difference as well as with effects in either direction under that calculation. The registry’s adjusted odds-ratio interval and the recalculated risk-difference interval are on different scales and arise from different analyses; they should not be compared as if they were estimates of the same quantity.

For the severe-flare analysis, the reported hazard ratio is 0.77 and its 95% confidence interval is 0.51 to 1.17. This interval includes 1, so it includes the null value for a hazard ratio. Its p-value is 0.226. The interval spans effects on both sides of the null, and therefore does not precisely establish the direction or magnitude of the comparison.

Confidence intervals describe uncertainty under the specified statistical procedure; they do not account for every possible source of uncertainty, such as unreported analysis choices, selection into the open-label extension, or limitations in generalizing beyond the studied population. No confidence interval should be read as a guarantee that the true effect lies inside its endpoints. The reported intervals are most useful when considered together with the outcome definition, analysis population, and model that produced them.

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 planning illustrations use the observed effect as a reference and show alternative assumptions for detecting the full observed effect or a stated fraction of it. For binary outcomes, the figures are participants per arm. For the time-to-event outcome, the figures are total events, not participants per arm. The primary response illustration lists 782 participants per arm for 80% power and 1,046 participants per arm for 90% power when planning for 100% of the observed effect. For 75% of the observed effect, the corresponding figures are 1,386 and 1,854 participants per arm; for 50%, they are 3,105 and 4,156.

In plain language, the 80% power column is the planning size associated with an 80% chance of detecting the specified effect if that effect is the true one and the stated assumptions hold. The 90% power column uses a higher target chance of detection and therefore requires more information under the same assumptions. Smaller effects are harder to distinguish from ordinary sampling variation, so planning to detect a smaller fraction of the observed effect requires more participants per arm. For time-to-event planning, the analogous figures count total events rather than people enrolled.

The stated planning assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation, with the effect set to the stated fraction of the observed effect. For time-to-event outcomes, the calculation uses the Schoenfeld approach. These are planning illustrations computed from the observed effect, not the trial’s original design assumptions, which are not reported in the registry record. They are not observed power: they do not describe the probability that this completed study had a significant result after its outcomes were observed.

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 = 0.416; treatment proportion p₁ = 0.487; average p̄ = 0.451.
2. First term: z_1−α/2 × √[2p̄(1−p̄)] = 1.96 × 0.7038 = 1.3793.
3. Second term: z_1−β × √[p₀(1−p₀) + p₁(1−p₁)] = 0.842 × 0.7020 = 0.5908.
4. n = (1.3793 + 0.5908)² / (0.0705)² = 781.6, rounded up to 782 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 <- 0.416107382550336                          # control proportion
p1 <- 0.486577181208054                          # 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(1632241)
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 = 782 (80% power), 1,046 (90% power)
 75% of observed effect: n per arm = 1,386 (80% power), 1,854 (90% power)
 50% of observed effect: n per arm = 3,105 (80% power), 4,156 (90% power)
power.prop.test: 781.6 
Simulated power at n = 782 per arm: 0.801 (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. Analyses Reported by the Sponsor

The registry’s own primary analysis is a logistic regression comparison reported as an odds ratio of 1.40, with a 95% confidence interval from 0.93 to 2.11 and p = 0.107. It is the covariate-adjusted analysis described in the endpoint record, including treatment group, baseline disease-activity category, baseline complement status, and region.

The recalculation is a simple unadjusted comparison based on the posted responder counts and denominators. Its p-value is 0.159, and the recalculated risk-difference interval includes zero. It uses a different measure and does not adjust for the listed covariates. The estimates and p-values therefore need not match exactly, even when they are based on the same posted endpoint.

The registry record does not flag a discrepancy between the reported analysis and the recalculation. The adjusted odds ratio is the result to use when describing the sponsor’s stated analysis; the recalculation provides a separate descriptive check on the posted counts. Neither result should be mistaken for evidence that the groups are identical, and neither by itself measures clinical importance.

15. Multiplicity, Missing Data and Analysis Populations

The registry record lists a primary endpoint and multiple secondary outcomes, but it does not report a complete multiplicity strategy for the family of statistical tests. Multiplicity matters when several outcomes, time points, or analyses are considered: without an appropriate plan, the chance of at least one apparently positive result by chance can increase. The record does not state whether a hierarchical testing sequence, adjustment procedure, or another method was used to control that risk. The reported p-values should therefore be interpreted outcome by outcome, with particular caution about treating secondary results as confirmatory.

The primary endpoint description does specify the analysis population and an important outcome rule. The modified intention-to-treat population was the safety population excluding participants assessed at sites 202196, 202513, or 107286. Drop-outs and treatment failures were assigned non-responder status. One participant in the belimumab group lacked a screening or baseline PGA assessment and did not contribute to the SRI or component analysis. These details clarify some aspects of the primary analysis but do not supply a complete account of missing data across the trial.

Other missing-data procedures, including any imputation beyond the stated non-responder rule, are not reported in the registry record. It is also not reported how missing covariates, incomplete follow-up, or participants with unavailable assessments were handled in every secondary analysis. For the time-to-event endpoint, censoring details are not reported. Those omissions limit independent assessment of the assumptions behind the estimates.

The registry record does not report the original sample-size justification or the full prespecified statistical analysis plan. It also does not report whether interim analyses were conducted. These are distinct issues: the planning illustrations use observed effects and stated illustrative assumptions, while the original design rationale and any interim-monitoring procedures are not reported in the registry record. No inference about those unreported procedures is warranted from the posted outcome results.

16. 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: pneumonia (3.6%), pericarditis (1.8%), lupus nephritis (1.2%), urinary tract infection (1.2%), systemic lupus erythematosus (0.9%).

For the double-blind phase, the serious adverse event figures list 31 affected participants among 165 at risk in the placebo group and 36 among 331 at risk in the belimumab group. The registry also records zero deaths in the placebo group and 2 in the belimumab group. These are counts with their listed at-risk denominators; they should be read as descriptive safety information rather than as a complete assessment of comparative risk.

The record lists pneumonia at 3.6% among the leading serious adverse event terms, followed by pericarditis at 1.8%, lupus nephritis at 1.2%, urinary tract infection at 1.2%, systemic lupus erythematosus at 0.9%, and acute myocardial infarction at 0.9%. These term percentages are registry entries and are not substitutes for the group-level serious-event counts.

Safety comparisons depend on outcome definitions, observation time, and how events were collected and attributed. The record does not provide enough detail in these figures to determine whether events were related to treatment or to make a complete adjusted comparison between groups. Open-label safety groups are also separate from the double-blind randomized comparison. These data describe what was recorded; they do not by themselves establish a causal explanation for an event.

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

The primary result describes the proportion meeting a composite SRI response definition at Week 52 in the modified intention-to-treat population. The posted response percentages were 41.6% for placebo plus standard therapy and 48.7% for belimumab 10 mg/kg plus standard therapy. The sponsor-reported adjusted odds ratio is 1.40, with a 95% confidence interval of 0.93 to 2.11 and p = 0.107. The interval includes the null value for an odds ratio, and the p-value is above the conventional 0.05 threshold.

This does not show that the treatments have identical effects. A result that does not cross a conventional statistical threshold can reflect a small effect, uncertainty in the estimate, or both. Conversely, a higher observed response percentage does not alone establish that the difference is reliable, clinically important, or caused by treatment. Statistical evidence and clinical importance are different questions, and the registry record does not supply a threshold for deciding what size of difference would be clinically meaningful.

The result also applies to a specific population, endpoint definition, treatment regimen, and analysis. The trial concerns adults of Black race with SLE, compares belimumab plus standard therapy with placebo plus standard therapy during the double-blind phase, and assesses response at Week 52. It does not, by itself, answer every question about other populations, treatment schedules, outcomes, or follow-up periods.

Secondary findings offer additional outcome-specific information but are limited by their different definitions and settings. The open-label extension is not equivalent to a continued blinded placebo comparison, and the record does not report a complete multiplicity plan. Safety counts should likewise be interpreted as recorded events rather than a full causal assessment. Taken together, the registry results support a careful description of the measured comparisons, not a broad treatment recommendation or a conclusion that every possible outcome has been resolved.

18. Why This Trial Matters Statistically

This study is statistically informative because its primary outcome is a composite response rather than a single measurement. The definition combines improvement in disease activity with limits on worsening in PGA and BILAG organ-domain scores. That structure makes the interpretation dependent on the full response rule: a participant must satisfy all its components to be counted as a responder. The resulting percentage is therefore meaningful only when read alongside that definition and the stated non-responder rule for drop-outs and treatment failures.

The record also illustrates why adjusted and unadjusted measures should be distinguished. The sponsor’s logistic regression reports an adjusted odds ratio, while the recalculation summarizes the posted counts without the listed covariate adjustment. Both can be useful, but they answer different statistical questions. Reporting the model, covariates, analysis population, and endpoint definition allows readers to understand what the estimate represents.

Precision is central to the interpretation. The primary confidence interval includes the odds-ratio null, and the corresponding p-value is above the conventional threshold. The result should not be reduced to the direction of the point estimate alone. The interval communicates that the data do not tightly isolate a single effect value, while the secondary time-to-event result likewise has an interval that includes its null value.

The trial record also gives an opportunity to distinguish randomized blinded evidence from open-label follow-up. Treatment histories differ in the extension, which changes what can be inferred from between-group outcome contrasts. Finally, the registry’s omissions around multiplicity, original sample-size planning, and some missing-data details matter: statistical interpretation depends not only on estimates, but also on how the analysis was planned and how incomplete observations were handled.

19. 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 analysis population for the primary endpoint is narrower than the overall safety population because assessments from three sites were excluded. The registry provides the site identifiers and the mITT definition, but does not explain why those sites were excluded. That limits assessment of the reason for, and possible consequences of, the exclusion.

The endpoint is a composite, and its response classification depends on multiple components. The record specifies the response criteria and states that drop-outs and treatment failures were set to non-responders, but it does not report a complete account of missing-data handling for all components or secondary outcomes. One belimumab-arm participant lacked a screening or baseline PGA assessment and did not contribute to the SRI or component analysis.

The primary adjusted analysis and the unadjusted recalculation use different effect measures and adjustment sets. The registry reports the logistic model covariates, but does not provide a full statistical analysis plan or all information needed to independently assess model assumptions and diagnostics. The original sample-size justification, any interim analyses, and comprehensive multiplicity handling are not reported in the registry record.

Some secondary information comes from an open-label extension. The groups have different prior treatment histories, and this period does not preserve the same placebo-controlled randomized contrast as the double-blind phase. The available safety figures are descriptive and do not include enough information to establish treatment attribution or a fully adjusted comparative safety estimate. These limitations constrain interpretation of the posted results; they do not change the values reported for the specified analyses.

20. Related Tutorials

21. Related Statistical Calculators

22. Sources

• ClinicalTrials.gov: Efficacy and Safety of Belimumab in Black Race Patients With Systemic Lupus Erythematosus (SLE) — NCT01632241.
• Registry record last updated 2021-09-08; status last verified 2021-08.
• Results first posted 2019-07-05.
• 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.

23. Record Summary

The registry record describes a completed Phase 4, multicenter, randomized, double-blind, placebo-controlled, parallel-group study of belimumab 10 mg/kg plus standard therapy versus placebo plus standard therapy in adults of Black race with SLE. Enrollment is recorded as 503. The primary endpoint was the Week 52 percentage achieving an SRI response with modified SLEDAI-2K scoring for proteinuria.

Primary response percentages were 41.6% with placebo and 48.7% with belimumab. The sponsor-reported adjusted odds ratio was 1.40, with a 95% confidence interval of 0.93 to 2.11 and p = 0.107. The confidence interval includes the odds-ratio null. The registry also reports secondary response, flare, open-label, and safety outcomes, each requiring interpretation in its own analysis setting.

The record does not report the original sample-size justification, complete multiplicity procedures, interim analyses, or all missing-data details. These omissions limit how fully the statistical plan can be evaluated from the registry record.