A Study of PRCL-02 in Moderate to Severe Chronic Plaque Psoriasis: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for A Study of PRCL-02 in Moderate to Severe Chronic Plaque Psoriasis (NCT03614078), a randomized phase 2 study. The primary outcome is Percentage of Participants Achieving Psoriasis Area and Severity Index ≥75% (PASI 75) Improvement.

2. Clinical Question

3. Trial Design

The registry identifies this as a Phase 2a study of PRCL-02 in patients with moderate to severe chronic plaque psoriasis. Its stated aim was to evaluate safety, tolerability, and efficacy. The trial is described as randomized, double-masked, and using a parallel-group model. It was completed. The registry enrollment is 92, and the recorded start date is 2018-09-25, with primary completion on 2019-04-29.

Three treatment groups are represented in the primary outcome results: PRCL-02 25 mg, PRCL-02 50 mg, and placebo. Both active regimens used a loading dose followed by a once-daily maintenance dose beginning on Day 2 and continuing for 12 weeks. Placebo followed a matching schedule and treatment levels. The primary endpoint timeframe is baseline to week 12, following 12 weeks of treatment.

The primary outcome summaries list 30 participants in the 25 mg group, 29 in the 50 mg group, and 31 in the placebo group. These are the denominators attached to the primary outcome data, not an explanation of how all enrolled participants were assigned or followed. The registry record does not explain the relation between the overall enrollment of 92 and these arm-specific outcome denominators. Nor does it report the randomization procedure, allocation ratio, concealment procedures, masking details, or reasons for any difference between enrollment and the endpoint denominators.

Four secondary outcomes are listed: participants with any treatment-emergent adverse event, area under the concentration-time curve, maximum observed drug concentration, and time to maximum observed drug concentration. The registry also posts adverse-event summaries. Further detail on the conduct of the trial, including site information and protocol procedures, is not reported in the registry record. The design information supports describing the broad comparison, but not reconstructing unreported operational or statistical details.

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.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Intent to treat population

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: Safety population

6. Primary Endpoint

The registry lists the primary outcome as Percentage of Participants Achieving Psoriasis Area and Severity Index ≥75% (PASI 75) Improvement, measured over Baseline to week 12.

The primary endpoint is the number of participants achieving PASI 75 from baseline to week 12. The registry describes the Psoriasis Area and Severity Index as a measure of disease severity on a scale from 0 to 72, with 72 indicating extreme disease severity. PASI 75 denotes at least 75% improvement from baseline in that score by Week 12. The endpoint is therefore a binary response: each participant either meets the stated improvement threshold or does not.

A threshold-based endpoint can make a clinical outcome easier to interpret than a score change alone: it records how many participants crossed a prespecified level of improvement. However, it does not show the full distribution of score changes. Participants just short of the threshold and participants with little change are both counted as not achieving PASI 75, while the endpoint does not distinguish degrees of improvement among responders. Continuous PASI changes and other thresholds are not reported in the registry record.

The posted primary result is expressed as counts of participants, and the comparison estimates are risk differences. The endpoint is listed for the intent-to-treat population, but the procedures for handling missing endpoint data and the exact analysis population construction are not reported in the registry record. The result consequently describes the threshold response as posted, rather than every dimension of psoriasis severity or treatment experience.

7. Results Posted in the Registry

• PRCL-02 25 Milligrams (mg): 13.3% (4/30) versus 0.0% (0/31) on control; risk difference 13.3 percentage points (95% CI 1.2 to 25.5); unadjusted two-proportion z-test p = 0.035.
• PRCL-02 50 mg: 3.4% (1/29) versus 0.0% (0/31) on control; risk difference 3.4 percentage points (95% CI -3.2 to 10.1); unadjusted two-proportion z-test p = 0.297.

8. Statistical Interpretation

9. Statistical Methods Explained

What does a risk difference express?

The endpoint records whether each participant achieved PASI 75, so the comparison is between response proportions in the treatment and placebo groups. A risk difference expresses the absolute difference between those proportions, with the treatment group compared against placebo. A value above zero represents a higher observed response proportion in the active group; a value below zero represents a lower one. The posted risk differences are 0.133 for PRCL-02 25 mg versus placebo and 0.035 for PRCL-02 50 mg versus placebo.

The registry posts counts alongside these comparisons: 4 of 30 in the 25 mg group, 1 of 29 in the 50 mg group, and 0 of 31 in the placebo group. Because the placebo count is zero, these results are based on few observed responders. With sparse binary outcomes, each participant’s response can have a noticeable influence on the estimated group difference. The estimates should therefore be read together with their intervals, not as exact or stable quantities.

How should the confidence intervals and p-values be read?

A confidence interval describes the statistical uncertainty around an estimated difference under the assumptions of the analysis. It gives a range of values compatible with the data and method at the stated confidence level; it is not a guarantee that the true difference lies in the interval, nor does it give the probability that a treatment effect has a particular value. The 25 mg comparison has a 95% confidence interval from 0.012 to 0.255. For 50 mg, the 95% confidence interval runs from -0.032 to 0.101 and includes zero.

The posted p-values are unadjusted: 0.035 for the 25 mg comparison and 0.297 for the 50 mg comparison. A p-value measures how unusual data at least as incompatible with a specified null model would be if that model and the analysis assumptions held. It is not the probability that the null hypothesis is true, nor a measure of clinical importance. The registry record does not describe the inferential test or model used to produce the posted comparisons. It also does not report an adjustment for the multiple dose comparisons.

What can be said about the analysis population?

The primary endpoint is identified as applying to the intent-to-treat population. This label generally indicates analysis according to randomized assignment, but the exact operational definition, including how participants with missing endpoint data were treated, is not reported in the registry record. The endpoint summaries list arm-specific denominators, but the record does not explain whether these include all randomized participants or how they relate to the enrollment total. It would be inappropriate to assume an unreported imputation rule, exclusion rule, or sensitivity analysis.

The registry record does not report the planned statistical analysis method, covariate adjustment, stratification factors, interim analyses, or a sample-size justification. The comparison estimates and p-values can be described as posted, but these missing details limit independent reconstruction of the analysis and assessment of whether it followed a prespecified plan. The record also does not report whether the primary endpoint was assessed by blinded evaluators or how scoring consistency was maintained.

How do planning illustrations differ from trial results?

Sample-size planning illustrations based on an observed effect are not evidence about the trial’s achieved power. They are hypothetical calculations for a future study under stated assumptions. The record describes such planning assumptions as a two-sided significance level of 0.05, equal allocation between two arms, a normal approximation, and an effect to detect defined as a stated fraction of the observed effect. For non-time-to-event outcomes, the planning quantity is participants per arm. These assumptions do not establish that they were used to design this trial. The trial’s own design justification and target sample size are not reported in the registry record.

More generally, a planning calculation depends on the effect chosen for detection, the variability or event rate assumed, the significance level, and the desired power. An observed effect from a small number of responders can be an unstable basis for future planning. Any illustration derived from it should therefore be treated as conditional, not as a claim that the trial had a certain probability of detecting an effect, and not as a substitute for the missing design rationale.

Why does sparse binary data matter?

For a binary endpoint, the information is concentrated in the number of responders and nonresponders. When only a few responders are observed, estimates can be imprecise and methods may behave differently depending on their assumptions. The 25 mg and placebo counts are 4 and 0, respectively; the 50 mg and placebo counts are 1 and 0. The resulting confidence intervals are important because they show that uncertainty remains even when a point estimate favors an active group. The registry does not report the exact estimation procedure, so no claim can be made about whether a particular small-sample method was used.

Over-dispersion is a general concern when observed variability exceeds that assumed by a statistical model; in binary outcomes, one might also consider whether outcomes cluster or differ systematically across participants or sites. The record does not report clustering or an over-dispersion assessment, so this is a general methodological consideration, not a finding about this trial. Likewise, adjustment for baseline characteristics can sometimes improve precision, but adjusted results are not reported in the registry record. The posted estimates are best interpreted as the displayed arm comparisons, with their stated uncertainty and the analysis details that remain unavailable.

10. Confidence Intervals and Precision

The precision of a treatment comparison is conveyed more directly by its confidence interval than by the point estimate alone. For PRCL-02 25 mg versus placebo, the posted risk difference is 0.133, and the 95% confidence interval extends from 0.012 to 0.255. Although this interval is entirely above zero, it covers a range of possible differences that varies appreciably in magnitude. The estimate is therefore not a precise determination of the size of the group difference.

For PRCL-02 50 mg versus placebo, the posted risk difference is 0.035 and its 95% confidence interval extends from -0.032 to 0.101. Because the interval includes zero, the data do not sharply distinguish a positive difference from no difference or a negative difference under the stated comparison. The p-value of 0.297 is consistent with that uncertainty; it does not show that the groups are equivalent.

Both comparisons have few observed responders, and this limits the amount of information available about the response difference. Zero responders in the placebo group does not mean the underlying response probability is known to be zero. A sample can observe no events even when the underlying probability is not exactly zero. The interval reflects uncertainty in the comparison, though the registry record does not report the precise interval method.

The posted intervals concern the specific PASI 75 endpoint, comparison, and follow-up period. They do not quantify uncertainty for other outcomes, later time points, or a direct comparison between the two PRCL-02 dose groups. The registry record does not report adjusted confidence intervals or multiplicity-adjusted inference. Thus, the intervals are useful for understanding the uncertainty in each posted comparison, but do not resolve questions about analysis choices or broader generalizability.

11. Multiplicity, Missing Data and Analysis Populations

Multiplicity arises when several hypotheses are examined. If a trial compares more than one dose with placebo, the chance of at least one apparently unusual result can differ from the chance associated with a single comparison. This trial posts two dose-versus-placebo comparisons. Their p-values, 0.035 and 0.297, are unadjusted. The registry record does not report a multiplicity adjustment, a testing sequence, or a rule for identifying which comparison should be considered primary for inferential purposes. The lower unadjusted p-value should therefore not be interpreted as though it necessarily accounts for both comparisons.

The record identifies the primary population as intent to treat. That designation is useful, but it does not specify what happened to participants with missing PASI measurements, protocol deviations, or other incomplete information. Missing-data procedures, sensitivity analyses, and reasons for any absent primary outcome are not reported in the registry record. The arm denominators for the primary outcome are 30, 29, and 31, while overall enrollment is 92; the record does not explain the relationship between these quantities. It is not possible to infer the handling of missing outcomes from the reported counts alone.

Other analysis details that affect interpretation—including the exact statistical test or model, any adjustment for baseline variables, and the analysis plan for secondary outcomes—are not reported in the registry record. The presence of four listed secondary outcomes does not indicate how their results were tested or whether they were part of a multiplicity strategy. No interim analyses or stopping rules are described in the record. These omissions do not change the posted endpoint counts, but they limit assessment of the inferential framework and how confirmatory the comparisons were intended to be.

12. Safety Results

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

Deaths

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 5% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: measles (3.2%).

The registry posts serious adverse event counts for the safety groups: 1 participant in the PRCL-02 25 mg group, 0 in the PRCL-02 50 mg group, and 0 in the placebo group. The corresponding numbers at risk are 31, 30, and 31. The record lists zero deaths in each group. These are counts within the recorded groups; they do not by themselves establish whether an event was caused by treatment.

The record also lists other treatment-emergent adverse events affecting 3 participants in the 25 mg group, 3 in the 50 mg group, and 4 in the placebo group. These figures are separate from the serious-event counts. The registry identifies measles, at 3.2%, as the top serious-event term. It does not provide enough detail in these summaries to establish the clinical context, timing, course, or causal attribution of that term. A term’s appearance in a safety listing should not be read as proof that the treatment caused it.

The safety denominators differ from the primary endpoint denominators: the safety groups list 31, 30, and 31 at risk, while the primary results list 30, 29, and 31. The registry record does not explain the difference. These safety counts are descriptive and should be interpreted in light of the trial’s 12-week treatment period and the limited group sizes. They do not establish the frequency of uncommon events or safety beyond the recorded follow-up.

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

The posted results show that PASI 75 was observed in 4 participants receiving PRCL-02 25 mg, 1 participant receiving PRCL-02 50 mg, and no participants receiving placebo during the baseline-to-week-12 assessment. The comparison estimate for 25 mg is above zero, with a 95% confidence interval that also lies above zero. The estimate for 50 mg is smaller and its 95% confidence interval includes zero. These are descriptions of the observed trial data and their statistical uncertainty, not conclusions about how an individual patient would respond.

The findings do not establish that one dose is better than the other. The registry posts each dose against placebo, not a direct 25 mg versus 50 mg comparison, and the number of observed responders is limited. The record does not report an adjustment for the two dose comparisons. The unadjusted p-value for the 25 mg comparison should therefore be interpreted with that missing multiplicity information in mind. The 50 mg result does not demonstrate equivalence or rule out meaningful differences; its interval remains compatible with values on either side of zero.

Nor do these results describe every aspect of treatment response. PASI 75 is a threshold outcome; it does not show the distribution of score changes or other degrees of improvement. The endpoint was assessed at week 12, so the posted result does not establish persistence beyond that time. The record does not report additional follow-up results for this primary endpoint, nor does it report enough information to assess missing-data assumptions or reconstruct the planned analysis.

The safety counts provide a limited descriptive account, not a comprehensive estimate of risk. They concern the recorded events and groups during the study, with no deaths listed. Small group counts cannot settle questions about uncommon events, and the record does not establish causation for reported events. The overall conclusion should remain bounded: the registry describes sparse PASI 75 responses and uncertain group differences at week 12, alongside adverse-event counts, in a completed Phase 2a trial. Wider clinical conclusions are not established by these data alone.

14. Why This Trial Matters Statistically

This trial is statistically informative as an example of how a binary endpoint can produce apparently different point estimates while leaving substantial uncertainty about the size of the differences. The primary outcome reduces a change in PASI score to whether a participant achieved the stated 75% improvement threshold. That can make a response easy to define, but it also discards information about changes that fall short of or exceed the threshold. Counts and confidence intervals are therefore essential to interpreting the headline comparison.

The sparse number of observed responders is central to reading the results. The 25 mg group had 4 responders and the 50 mg group had 1, compared with none in placebo. A zero count in a comparator group can make the observed risk difference look clear in direction, while the underlying response probability and the precise effect remain uncertain. The confidence intervals expose some of that uncertainty and help prevent a point estimate from being mistaken for a settled effect size.

The two unadjusted dose comparisons also illustrate why a statistical analysis plan matters. With multiple comparisons, interpretation depends in part on whether a hierarchy or adjustment was planned. Because this information is not reported in the registry record, the results cannot be evaluated as a complete multiplicity-controlled testing strategy. The contrast between the 25 mg and 50 mg results also cautions against inferring a dose pattern from separate placebo comparisons, particularly without a direct active-dose comparison.

Finally, the registry’s enrollment, primary outcome denominators, and safety denominators are not reconciled in the record. Missing-data handling and the detailed statistical method are also not reported. Those gaps do not erase the posted numbers; they define what can be interpreted confidently. The trial offers a concrete illustration of the importance of endpoint definitions, denominators, precision, multiplicity, and transparent reporting in clinical research.

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.

Several limitations are specific to the posted record. The primary outcome is a threshold response at week 12, rather than a full account of change in PASI or response over time. The registry does not report continuous PASI results, alternative response thresholds, or longer-term primary endpoint results. Conclusions are consequently restricted to PASI 75 at the stated assessment.

The observed responder counts are limited: 4 in the 25 mg group, 1 in the 50 mg group, and 0 in placebo. This sparseness is reflected in the uncertainty around the risk differences, particularly the interval for the 50 mg comparison, which includes zero. The registry does not report the exact estimation method, model adjustments, or small-sample procedures used. The p-values are unadjusted, and a multiplicity plan is not reported.

The record identifies an intent-to-treat population but does not describe missing-data procedures or explain how endpoint denominators relate to enrollment. The primary outcome arm summaries list 30, 29, and 31 participants; the safety summaries list 31, 30, and 31 at risk; enrollment is 92. The reasons for these differences are not reported in the registry record. This limits assessment of whether the endpoint and safety summaries represent the same participant sets.

The safety results are also limited by their descriptive form and group sizes. They cannot establish the occurrence or absence of uncommon events, and the record does not establish that a reported event was caused by treatment. Follow-up for the primary endpoint is 12 weeks. Details such as the randomization procedure, masking implementation, site effects, protocol deviations, and the trial’s own sample-size justification are not reported in the registry record. These gaps constrain evaluation without changing the reported observations.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: A Study of PRCL-02 in Moderate to Severe Chronic Plaque Psoriasis — NCT03614078.
• Registry record last updated 2020-03-30; status last verified 2020-03.
• Results first posted 2020-03-30.
• 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.

19. Record Summary

NCT03614078 is a completed, randomized, double-masked, parallel-group Phase 2a study of PRCL-02 in moderate to severe chronic plaque psoriasis. The registry lists enrollment of 92 and a primary endpoint of PASI 75 from baseline to week 12 in the intent-to-treat population. The posted counts were 4 of 30 for PRCL-02 25 mg, 1 of 29 for PRCL-02 50 mg, and 0 of 31 for placebo. The risk differences versus placebo were 0.133 and 0.035, respectively, with 95% confidence intervals of 0.012 to 0.255 and -0.032 to 0.101. The record also posts adverse-event counts and four secondary outcomes. Details of multiplicity handling, missing-data procedures, and the full statistical analysis plan are not reported in the registry record.