Multiple Ascending Doses of Rozibafusp Alfa (AMG 570) in Adults With Rheumatoid Arthritis: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Multiple Ascending Doses of Rozibafusp Alfa (AMG 570) in Adults With Rheumatoid Arthritis (NCT03156023), a randomized phase 1 study. The primary outcome is Number of Participants With Treatment-emergent Adverse Events.

2. Clinical Question

3. Trial Design

This was a randomized, quadruple-masked, parallel-group Phase 1 study of rozibafusp alfa in adults with rheumatoid arthritis. The registry record lists an enrollment of 34 and a completed status. The study start date was 2017-08-14, and the primary completion date was 2019-10-17. Amgen is listed as the sponsor.

Participants were assigned to rozibafusp alfa dose groups or matching placebo. The described active doses were 70 mg, 140 mg, 210 mg and 420 mg. Treatment was subcutaneous and scheduled once every 2 weeks for up to 10 weeks, for 6 doses. The record indicates that escalation to a higher dose cohort depended on a review of the previous dose regimen, but the available description ends before the full criterion is stated. The details of how participants were allocated among dose groups, and the number assigned to each group beyond the posted safety counts, are not reported in the registry record.

Masking was listed as quadruple, but the specific roles of the masked parties are not reported in the registry record. A parallel design means participants were assigned to a group and evaluated in that group rather than described as crossing between treatments. The primary endpoint concerned treatment-emergent adverse events. Secondary outcomes focused on rozibafusp alfa pharmacokinetics, including time to maximum observed concentration, maximum serum concentration, area under the concentration-time curve, terminal half-life and accumulation measures. These outcomes address drug exposure and its change over repeated dosing; they are distinct from clinical efficacy outcomes.

The registry record does not report a detailed protocol for dose escalation, allocation concealment, or the planned statistical analysis. Those omissions limit what can be concluded about the design beyond the listed features.

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: The study consisted of 4 multiple ascending dose cohorts. Within each cohort participants were randomized in a 3:1 ratio to receive rozibafusp alfa or placebo. Escalation to a higher dose cohort was contingent on a review to confirm that the previous dose regimen(s) demonstrated an acceptable safety and tolerability profile.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: All randomized participants who received at least 1 dose of rozibafusp alfa or placebo.

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: All randomized participants who received at least 1 dose of rozibafusp alfa or placebo.

6. Primary Endpoint

The registry lists the primary outcome as Number of Participants With Treatment-emergent Adverse Events, measured over From first dose of study drug to 24 weeks after last dose (up to 34 weeks)..

The primary endpoint counted participants with treatment-emergent adverse events. An adverse event was defined in the registry as an untoward medical occurrence, including worsening of a pre-existing condition or clinically significant changes in laboratory tests or physical examination. The event did not need to be judged causally related to study treatment. The assessment period began with the first dose and continued through 24 weeks after the last dose, up to 34 weeks.

Adverse events were graded using CTCAE Version 4, with severity levels ranging from mild through death. The record also defines serious adverse events by criteria such as fatality, life threat, hospitalization, persistent or significant disability, congenital anomaly or another medically important event. Investigators assessed whether each event was related to study drug.

Counting affected participants is useful in an early-phase study because it provides a descriptive account of the number of people who experienced events during treatment and follow-up. It can help characterize the observed safety experience across dose groups. However, a participant count does not by itself describe the number of separate event episodes, their duration, or their severity distribution. Nor does an event count establish that treatment caused an event. The endpoint is a safety measure, not a measure of improvement in rheumatoid arthritis. The registry record does not report a single statistical comparison for this endpoint.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does a participant count measure?

For a binary safety outcome, each participant is classified according to whether the specified event occurred during the defined observation period. A count can be informative because it makes the observed number of affected participants explicit. It is important to keep the denominator in view: a count from a group with few participants can change substantially when the status of one participant differs. Counts are therefore best read alongside the number at risk in each group, rather than as standalone evidence of a treatment difference.

The primary endpoint counts participants with treatment-emergent adverse events. It does not count every adverse event episode, and it does not state how many events an individual participant had. The posted serious-event counts are a separate classification. The registry definition makes clear that adverse events do not necessarily have a causal relationship with study treatment; the investigator assessed relatedness. Event occurrence, severity, seriousness and treatment relatedness are distinct concepts and should not be collapsed into one measure.

Why is uncertainty important?

A statistical estimate based on a sample is subject to uncertainty because the observed participants do not necessarily represent every person who might meet the study criteria. A confidence interval, when reported, describes a range of values compatible with the data under the method’s assumptions. A narrow interval indicates greater precision than a wide interval, while neither interval alone establishes causation or clinical importance. The registry record does not report confidence intervals for the primary safety counts.

For small groups, conventional large-sample approximations can be unreliable, especially when event counts are very low or absent in a group. Exact methods or carefully chosen models may be considered in general for sparse binary outcomes, but the registry record does not report which method, if any, was planned or used for a comparison. It also does not report a p-value for the primary endpoint. A lack of a reported test is not evidence that groups are equivalent; it means the registry does not provide that inferential result.

How should multiple groups be understood?

The study includes placebo and several active dose groups, so a statistical analysis could pose multiple questions: each dose against placebo, trends across dose levels, or an overall difference among groups. These questions are not equivalent. When multiple hypotheses are tested, the chance of at least one false-positive finding can increase unless the analysis accounts for multiplicity. A dose trend analysis also requires a defined model and assumptions about how outcomes relate to dose. The registry record does not report which comparisons were planned, whether multiplicity was addressed, or whether a dose-response analysis was conducted.

What do the pharmacokinetic outcomes represent?

Pharmacokinetics describes how drug concentrations change over time. Maximum observed concentration refers to the highest measured serum concentration, and time to maximum concentration describes when that observed peak occurs. Area under the concentration-time curve summarizes exposure over a specified interval; terminal half-life characterizes the decline in concentration in the terminal phase. Accumulation measures compare exposure or peak concentrations across repeated dosing. These are general interpretations of the listed measures. Their actual values and uncertainty are not reported in the registry entries summarized for this analysis, so the outcome names cannot establish the exposure pattern or a dose relationship.

What can planning calculations say?

Sample-size planning asks how many participants may be needed to detect a defined effect under assumptions about the significance level, allocation and statistical method. Such a calculation is not a measure of the probability that a completed study detected an effect, and it does not alter the observed data. Planning illustrations based on an observed effect are particularly dependent on that effect estimate and should not be mistaken for the trial’s original design rationale. The registry record does not report a sample-size justification or the study’s own planning assumptions.

The record also does not report an analysis plan, interim analyses, missing-data procedures, or a statistical model for the primary outcome. Without these details, the reported counts can be described, but no unreported analysis should be attributed to the investigators.

10. Multiplicity, Missing Data and Analysis Populations

The study had multiple dose groups and multiple listed secondary pharmacokinetic outcomes. Each additional statistical comparison can create a multiplicity issue if several hypotheses are tested and interpreted together. A prespecified approach may control the overall false-positive risk, prioritize a primary comparison, or treat the analyses as exploratory. The registry record does not report whether any multiplicity strategy was planned or applied, and it does not provide a set of inferential comparisons for the primary endpoint. Consequently, the safety counts should be interpreted descriptively rather than as a collection of statistically confirmed group differences.

Missing-data handling is also not reported in the registry record. The primary outcome population is described as randomized participants who received at least one dose. The record does not explain how participants with incomplete follow-up were handled, whether all observed follow-up was included, or how missing adverse-event information was addressed. For a safety endpoint, length and completeness of observation can matter because participants may have different opportunities for events to be recorded. No assumptions about missing outcomes or follow-up should be inferred from the counts alone.

The registry record does not report a detailed analysis population for the secondary pharmacokinetic outcomes, an approach to missing concentration measurements, or rules for excluding measurements. It also does not report interim analyses or a statistical analysis plan. These gaps do not invalidate the posted descriptive counts, but they limit assessment of how the data were selected, compared and interpreted.

11. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Deaths

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 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 (16.7%), sepsis (16.7%), invasive ductal breast carcinoma (14.3%).

The serious adverse event counts are 0 of 8 participants for placebo, 1 of 7 for rozibafusp alfa 70 mg, 1 of 6 for 140 mg, 0 of 6 for 210 mg, and 0 of 7 for 420 mg. No deaths were listed in any group. The registry separately reports other adverse events for 7 of 8, 6 of 7, 6 of 6, 6 of 6 and 7 of 7 participants, respectively. These categories should be kept distinct: the “other” counts are not a substitute for the serious-event counts.

The serious-event terms listed most prominently are pneumonia and sepsis, each at 16.7%, and invasive ductal breast carcinoma at 14.3%. The registry does not specify the denominator behind these percentages, so their precise interpretation is limited. The term list does not establish how many participants in each treatment group experienced each event, whether events were related to study drug, or whether one participant contributed more than one event term.

Small group counts are descriptive and can be imprecise. They do not establish that one group has a greater or lesser underlying risk. The record defines seriousness and notes investigator assessment of relatedness, but the listed counts alone do not give a complete account of severity, timing, duration or causality for individual events.

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

The registry record documents a randomized, quadruple-masked Phase 1 study of multiple rozibafusp alfa doses and matching placebo in adults with rheumatoid arthritis. It reports the number of participants with serious and other adverse events in each group and lists selected serious-event terms. Those data describe the observed safety experience recorded for the study groups. They do not by themselves establish a causal relationship between treatment and an event, quantify a precise treatment effect, or show that groups are equivalent.

The primary endpoint was a count of participants with treatment-emergent adverse events over a defined follow-up period. The endpoint’s broad definition includes untoward medical occurrences that need not be treatment-related. Serious adverse events are a narrower category defined by specified seriousness criteria. The reported counts therefore need to be interpreted in light of the endpoint definitions, follow-up, group sizes and the absence of reported uncertainty estimates or inferential comparisons.

The study also listed pharmacokinetic outcomes, but their numerical results are not reported in the registry record for this analysis. The registry’s outcome titles alone do not demonstrate how concentration changed with dose or repeated administration. Likewise, the record does not report a sample-size justification or detailed statistical plan, so the enrollment cannot be interpreted as evidence that the study was designed to detect a particular difference.

These findings are specific to the study population, regimens and observation period described in the registry. They do not provide a basis for medical decisions or for conclusions about treatment effects on rheumatoid arthritis. The registry record offers a limited descriptive view, with important details about statistical comparisons, missing data and pharmacokinetic results not reported.

13. Why This Trial Matters Statistically

Early-phase randomized studies can provide structured observations across dose groups while retaining a placebo comparison. In this trial, the registry identifies a safety endpoint and pharmacokinetic outcomes, making clear that the study’s emphasis was safety, tolerability and drug exposure rather than a reported test of clinical benefit in rheumatoid arthritis. Recognizing the study’s question is essential when interpreting its results: a safety count is not an efficacy measure.

The multiple dose groups also raise statistical issues that are useful to recognize. Group counts can look different simply because of random variation, particularly when the groups are small. Comparisons across several doses require a clear plan for defining the relevant contrasts and addressing multiple testing. A dose-escalation design can make the sequence of decisions important, but the registry record does not fully describe the escalation criteria or statistical rules. These omissions mean that the listed dose groups should not be read as a formal dose-response finding.

The record also illustrates why endpoint definitions matter. “Any adverse event,” “serious adverse event,” severity and investigator-assessed relatedness capture different dimensions. Reporting participant counts is useful, but a fuller statistical interpretation would also consider uncertainty, follow-up completeness, event timing and the analysis population. Those details are not reported in the registry record.

Finally, pharmacokinetic outcomes and safety outcomes answer different questions. Concentration and exposure measures characterize drug disposition; they do not automatically establish clinical effect or explain adverse events. Separating these questions helps prevent descriptive data from being overstated. The trial is statistically informative as a record of the design and observed counts, while the absence of reported comparisons and detailed analysis methods limits the strength of broader conclusions.

14. Limitations

• The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
• Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.

The posted record has several limitations for statistical interpretation. Although the study is described as randomized, quadruple-masked and parallel, the specific allocation procedures and the roles included in masking are not reported. The dose-escalation description is incomplete: it states that advancement depended on review of the previous regimen, but the full decision criteria are not reported. These details matter for understanding how cohorts were formed and how dosing decisions were made.

The registry reports safety counts but does not provide inferential comparisons, confidence intervals or a detailed statistical analysis plan for the primary endpoint. It does not report a sample-size justification, so the adequacy of enrollment for a particular statistical objective cannot be assessed. The small number of participants in each listed group also means descriptive counts should not be mistaken for precise estimates.

Information about missing safety observations, follow-up completeness and analysis populations beyond the stated primary population is not reported in the registry record. The listed serious-event percentages have no stated denominator in the record, limiting their interpretation. Individual event timing, severity distributions and treatment-relatedness results are also not given in the registry record.

Although pharmacokinetic outcomes are listed, their numerical results are not reported in this record summary. Accordingly, no conclusions about concentration, exposure, half-life or accumulation can be drawn from the endpoint names. These limitations restrict the analysis to the design features and descriptive safety counts explicitly reported.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Multiple Ascending Doses of Rozibafusp Alfa (AMG 570) in Adults With Rheumatoid Arthritis — NCT03156023.
• Registry record last updated 2024-05-14; status last verified 2024-05.
• Results first posted 2023-04-03.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

18. Record Summary

NCT03156023 is a completed, randomized, quadruple-masked, parallel-group Phase 1 study of rozibafusp alfa in adults with rheumatoid arthritis. Enrollment was 34. Participants received matching placebo or rozibafusp alfa by subcutaneous injection once every 2 weeks for up to 10 weeks, with 6 doses; the active dose groups listed were 70 mg, 140 mg, 210 mg and 420 mg.

The primary outcome counted participants with treatment-emergent adverse events from the first dose through 24 weeks after the last dose, up to 34 weeks. The record provides group counts for serious and other adverse events and lists serious-event terms. It also lists pharmacokinetic secondary outcomes. Numerical pharmacokinetic results, inferential comparisons, a detailed statistical plan, missing-data procedures and sample-size justification are not reported in the registry record.