Safety and Efficacy of Abatacept in IgG4-Related Disease: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Safety and Efficacy of Abatacept in IgG4-Related Disease (NCT03669861), a na phase 2 study. The primary outcome is Treatment Response.

2. Clinical Question

In statistical terms, this study asks whether a complete-remission outcome was observed among participants receiving abatacept during the specified treatment period. A single-group study can describe outcomes in the enrolled participants, but it cannot by itself distinguish an intervention effect from changes that might have occurred over time, differences in participants’ disease course, or other influences. The registry record identifies several secondary outcomes, including disease response and changes in serum concentrations among responders, but does not report their results. The question is therefore descriptive and exploratory rather than a controlled estimate of comparative treatment effect.

3. Trial Design

This is a completed, Phase 2, single-center, open-label, single-group proof-of-concept study of abatacept in IgG4-RD. The registry records enrollment of 10 participants. Its summary describes participants with active disease receiving weekly subcutaneous abatacept at 125mg for 24 doses over 24 weeks. The planned primary assessment concerns complete remission at week 24.

Because the study has one group and no masking, participants and study personnel were not blinded to treatment assignment; there was no separate assignment to a comparator. The registry lists allocation as not applicable. These design features matter when interpreting an outcome: observations can describe what occurred among the enrolled participants, but the design does not create a concurrent control group against which to estimate a treatment contrast. Open-label assessment may also be susceptible to expectations or judgment, depending on how outcomes were defined and assessed. Details of outcome adjudication are not reported in the registry record.

The study dates recorded are a start date of 2018-11-13 and a primary completion date of 2020-04-10; the status is completed. The record identifies Massachusetts General Hospital as the sponsor. Additional sites are not reported in the registry record, while the official title describes the study as single center.

The record lists secondary outcomes covering disease response, response at week 24, flares over time per participant, and declines in serum IgG4 and IgE concentrations among responders. It identifies six outcome measures, but does not give results for those secondary outcomes in the information available. The protocol’s detailed eligibility criteria, follow-up beyond the stated treatment period, and analysis plan are not reported in the registry record. The study’s small enrollment and proof-of-concept purpose mean that its findings are best read as preliminary descriptions, not as a definitive comparison.

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: Concurrent glucocorticoid treatment was permitted but was required to be discontinued by week 4.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: The primary outcome, complete remission at week 24

5. Baseline Characteristics

The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.

Population: The primary endpoint is 24 weeks, because this is the duration of time patients were on active treatment. The protocol called for a final study visit at 36 weeks, three months after the patients discontinued their active treatment

6. Primary Endpoint

The registry lists the primary outcome as Treatment Response, measured over 24 weeks.

The primary endpoint is the count of participants achieving complete remission of IgG4-RD at week 24. It is defined as a participant count, rather than a continuous measure such as a laboratory concentration or a time-to-event quantity. The registry describes it as the effect of weekly subcutaneous abatacept on complete remission and specifies the assessment time as 24 weeks.

A remission endpoint can provide a clinically interpretable summary of whether participants met a defined disease state at a particular assessment. A count is straightforward to understand, but its interpretation depends on the precise remission criteria, how the outcome was assessed, and how participants without an assessment were handled. Those details are not reported in the registry record. The count alone would also not convey how uncertain the estimate is; an interval estimate can communicate that uncertainty when one is reported.

The number of participants achieving complete remission is not reported in the registry record. Consequently, the primary endpoint’s observed result, its denominator at assessment, and any estimate of precision cannot be described from this record. The stated enrollment of 10 does not establish that every enrolled participant contributed an evaluable week-24 outcome.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The primary outcome is a binary status summarized as a count: whether each participant met complete-remission criteria at week 24. A count reports how many participants had the event, while the denominator indicates how many participants were assessed or included in that analysis. For a complete interpretation, both are needed. The registry record names the endpoint and its timeframe but does not report the remission count or an analysis denominator.

What does a confidence interval add?

As a general statistical concept, a confidence interval expresses the uncertainty around an estimate under a specified statistical method. It helps distinguish a relatively precise estimate from one that remains compatible with a broad range of values. For a binary outcome, the interval is informed by the event count and denominator. With a small group, the interval may be wide, reflecting that a limited number of observations cannot pin down the underlying event rate precisely. No confidence interval for the primary outcome is reported in the registry record, so no such precision estimate can be interpreted for this study.

What can a p-value establish?

As a general concept, a p-value assesses how compatible observed data are with a stated statistical null model, given the assumptions of the test. It is not the probability that a treatment works, nor does it measure the magnitude or practical importance of an effect. A p-value also cannot compensate for the absence of a suitable comparison group. The registry record lists no statistical analyses and reports no p-value for the primary outcome. It is therefore not possible to discuss statistical significance for the remission endpoint.

Why does the single-group design matter?

In a randomized comparison, treatment groups can support a direct estimate of a contrast, subject to the conduct and assumptions of the analysis. This study instead has one group receiving abatacept. Its outcome count, if reported, would describe that group at the specified follow-up; it would not estimate the difference between abatacept and a control. General statistical adjustment cannot recreate the information from a concurrent randomized control when no such group is part of the design. The registry does not report a model-based comparative analysis.

The open-label design is another consideration. General statistical reasoning recognizes that knowledge of treatment can affect participant reports, clinical management, or outcome assessment, especially when an endpoint depends on judgment. Whether that possibility affected this study depends on its remission criteria and assessment procedures. Those procedures are not reported in the registry record, so the degree of susceptibility cannot be assessed.

How should planning calculations be read?

General sample-size calculations estimate how many participants a future study might need under chosen assumptions about the effect to detect, the significance level, allocation, and analysis method. They are planning illustrations, not evidence that a study had a particular chance of finding an effect after it was conducted. The assumptions described for the planning illustrations use a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation; the effect to detect is described as a stated fraction of the observed effect. For non-time-to-event outcomes, the illustrations are expressed as participants per arm for 80% power or another specified power level; time-to-event illustrations instead concern total events. These hypothetical two-arm calculations do not change the fact that the trial itself was single-group. Numerical planning outputs and the observed primary effect are not reported in the registry record here, and no planning value should be read as an observed trial result or as observed power.

Over-dispersion is a general concern when count data vary more than a chosen statistical model expects. If a model assumes less variability than the data have, standard errors can be too small and intervals or tests can appear more decisive than warranted. This primary endpoint is described as a count of participants with an event, not as a repeated count process, and no model for it is reported. The registry record therefore offers no basis to claim that over-dispersion was tested or modeled in this analysis.

The record lists six outcome measures and no analyses. It does not report the statistical method used for the primary endpoint, how confidence intervals would be formed, whether any adjustment was made, or how missing observations were treated. These are not minor technical details: they determine the analysis population, the estimate’s uncertainty, and the interpretation of any reported test. In their absence, the endpoint definition can be explained, but a numerical statistical analysis cannot be reconstructed from the registry record.

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("Abatacept")
n      <- c(10)
events <- c(3)
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  Abatacept  10  3  30.0  6.7  65.2  10.8  60.3  10.9  61.0

11. Multiplicity, Missing Data and Analysis Populations

The registry identifies six outcome measures, including complete remission, disease response, response at week 24, flares over time per participant, and declines in serum IgG4 and IgE among responders. Considering several outcomes creates a general multiplicity issue: when many statistical tests are conducted, the chance of at least one apparently unusual result can increase. Researchers may specify a primary outcome, prioritize secondary outcomes, or use a multiplicity adjustment. Whether any such strategy was prespecified or used is not reported in the registry record. No outcome-specific analyses or multiplicity adjustment are listed.

Missing data also affect interpretation. A week-24 endpoint requires knowing who had an outcome assessment and how participants without one were handled. The registry record does not report the number assessed for the primary endpoint, the reasons for any missing assessments, or a missing-data method. It also does not report whether the primary analysis included all enrolled participants or a defined subset. Enrollment of 10 should therefore not be treated as proof that 10 participants contributed to every endpoint.

The analysis populations are not described in the registry record. It is not possible to determine whether the outcome summaries followed an intention-to-treat approach, a per-protocol approach, or another definition. These omissions limit assessment of whether the analyses matched the intended study population and how sensitive results might be to missing outcomes. They also mean that a secondary result, if available elsewhere, would need its denominator and analysis population to be interpreted responsibly.

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 4% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: myocardial infarction (10.0%).

For the abatacept group, the registry records 10 participants at risk for serious adverse events and 1 participant affected. It records 10 at risk for other adverse events and 3 affected, with 0 deaths. Myocardial infarction is listed among the top serious adverse event terms at 10.0%. These figures are descriptive counts in the study group, not a comparison with another group.

The at-risk figures describe the group used for the safety summaries; they do not necessarily establish the number assessed for the primary endpoint. The registry does not provide event-level details, timing, duration, severity beyond the serious-event classification, or an assessment of causality. A listed serious event does not by itself show that abatacept caused it. Likewise, the absence of reported deaths in this group is a count for this study and does not establish the absence of risk.

Because the study is small and has no control group, the safety counts cannot quantify how event frequency differs from another treatment or from background occurrence. The myocardial infarction term and 10.0% figure should be read as the registry’s listed serious-event information, not as a comparative risk estimate.

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

The registry record establishes the study’s design and question: a completed, open-label, single-group Phase 2 proof-of-concept study of weekly subcutaneous abatacept in active IgG4-RD, with complete remission at week 24 as the primary outcome. It also records enrollment of 10 and descriptive safety counts. These details explain what the study set out to assess and the context in which its results would need to be interpreted.

The record does not report the number of participants achieving complete remission. It therefore does not support a statement about the observed primary outcome, the size of an outcome rate, or its precision. Nor does it report analyses for the listed secondary outcomes. The absence of a reported result in this registry record should not be mistaken for evidence that no response occurred; it means the outcome value cannot be established from this record.

Even a reported remission count would not, on its own, demonstrate a treatment effect. With one open-label group and no randomized comparator, changes over time cannot be separated from effects attributable to the intervention. The design is useful for describing outcomes in a small group and for a proof-of-concept purpose, but it cannot provide the same comparative evidence as a controlled trial.

The safety counts similarly describe events recorded among participants in the abatacept group. They do not establish causation or comparative safety. Taken together, the registry entries define the scope of the evidence that can be discussed: study conduct, the intended endpoint, and recorded safety information. Conclusions about efficacy, comparative benefit, or a broader population require outcome and analysis details that are not reported in the registry record.

14. Why This Trial Matters Statistically

This trial matters statistically because its design makes the distinction between an observed outcome and a treatment effect especially clear. A single-group study can record whether participants met a remission definition, but without a control group it cannot estimate what would have happened to comparable participants under another condition. This distinction remains important even when a study is described as proof-of-concept.

The planned primary outcome is a participant count at a fixed follow-up time. That framing is easy to communicate, but interpretation still depends on the event count, the denominator, and uncertainty around the estimate. Here, the primary count and its precision are not reported in the registry record. Calling attention to that gap prevents the study’s title or its intended endpoint from being mistaken for an observed result.

The small enrollment also highlights why precision and analysis transparency matter. Counts in a small group can be sensitive to individual observations, and a reader needs the analysis population and missing-data handling to understand the denominator. Those details are not reported in the registry record. The record also lists multiple outcome measures without reporting analyses or a multiplicity strategy, leaving the intended interpretation of secondary outcomes unclear.

Finally, the registry’s safety counts illustrate the difference between describing events and attributing them. Counts and a listed event term can document what was recorded, while a causal or comparative conclusion requires an appropriate design and additional information. The statistical value of this record lies in clarifying these boundaries, rather than supporting a conclusion that it does not report.

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 main limitation for interpreting efficacy is that the primary remission count is not reported in the registry record. Without that result, its denominator, or an uncertainty estimate, the primary outcome cannot be quantitatively assessed. The record also does not provide results for the listed secondary outcomes, despite naming disease response, flares, and serum concentration changes among responders.

The study is single-group and open-label, with no randomized comparator. This limits causal interpretation and leaves potential influences from disease course, assessment, and participant or investigator expectations unresolved. The record does not report the remission criteria, outcome-assessment procedures, or whether assessment was independent of knowledge of treatment.

Enrollment was 10, which limits the amount of information available for describing event frequencies and makes estimates potentially imprecise. The number enrolled does not establish how many completed follow-up or contributed to each outcome. Completion by participant, missing assessments, reasons for missingness, and analysis populations are not reported in the registry record.

The registry lists six outcome measures but does not report analyses or a multiplicity plan. It also does not report the statistical methods, uncertainty intervals, or any sensitivity analyses. For safety, event counts are available, but detailed event timing, causality assessment, and comparative data are not. These trial-specific limitations mean that the record supports a description of design and recorded safety counts, but not a comprehensive efficacy or comparative safety assessment.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Safety and Efficacy of Abatacept in IgG4-Related Disease — NCT03669861.
• Registry record last updated 2021-08-24; status last verified 2021-07.
• Results first posted 2021-08-24.
• 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

NCT03669861 is a completed Phase 2, single-center, open-label, single-group proof-of-concept study of abatacept in IgG4-RD, sponsored by Massachusetts General Hospital. The registry records 10 enrolled participants and describes weekly subcutaneous abatacept at 125mg for 24 doses over 24 weeks. The primary endpoint is the count of participants achieving complete remission at week 24.

The primary remission result and the results of the listed secondary outcomes are not reported in the registry record. No statistical analyses are listed. Safety information records 1 participant with a serious adverse event, 3 with other adverse events, and 0 deaths among 10 at risk; myocardial infarction is listed among the top serious terms at 10.0%. The single-group design supports descriptive interpretation, not a randomized treatment comparison.