Comparison of Metvix Photodynamic Therapy (PDT) With Its Vehicle in the Treatment of Photoaged Skin: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Comparison of Metvix Photodynamic Therapy (PDT) With Its Vehicle in the Treatment of Photoaged Skin (NCT00437320), a randomized phase 2 study. The primary outcome is Number of Participants With Severity of Photodamage.

2. Clinical Question

The scale covers visible photodamage severity, from no damage through mild and moderate damage to severe damage. Its score is an assessment of skin appearance and severity, rather than a direct measure of a biological process. The registry does not give a numerical comparison, confidence interval, or significance test for the primary outcome. Therefore, the research question can be described, but the posted record does not establish what answer the trial’s outcome data gave.

3. Trial Design

This was a completed, randomized Phase 2 trial with a parallel model and triple masking, sponsored by Galderma R&D. Enrollment was 32. The registry lists photoaged skin as the condition. The recorded start date was 2007-04-18 and the primary completion date was 2008-09-01.

The treatment descriptions use a half-face comparison: Metvix cream was applied to one half-face and vehicle cream to the other. Three groups differed by the time the creams were applied before red-light exposure: 1 hour, 2 hours, or 3 hours. Applications were made at Baseline, Weeks 4 and 8. In the 2 hour and 3 hour descriptions, the red-light source is identified as an Aktilite 128 lamp and exposure is described as 7 to 10 minutes. The description for the 1 hour group is truncated in the registry record, so its full light-source details are not reported there.

The registry classifies the trial as parallel, while the treatment descriptions describe a within-person, half-face comparison. These describe different features: the parallel classification identifies the overall trial model, while the half-face descriptions indicate that each participant’s face was divided between the cream and vehicle. The record does not explain the allocation procedure for treatment side, or how the three exposure-duration groups were assigned.

Triple masking indicates that masking was recorded, but the identities of the masked parties and the procedures used to maintain masking are not reported in the registry record. The record also does not report a sample-size justification, the planned statistical methods, or interim analyses. Although the trial is marked completed, completion status alone does not supply the missing outcome estimates or clarify the analysis methods.

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 32 participants were enrolled in the study and randomized in three different groups (1 hour group, 2 hour group, and 3 hour group).

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: ITT population included all enrolled and randomized participants. "Here, 'Overall number of participants analyzed' signifies participants who were evaluable for this outcome measure. As per planned analysis data was separately analyzed and collected for both Metvix cream and Metvix vehicle cream based on 1, 2 and 3 hours group."

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: Intent-to-treat (ITT) population included all enrolled and randomized participants.

6. Primary Endpoint

The registry lists the primary outcome as Number of Participants With Severity of Photodamage, measured over At Week 20.

The primary endpoint is titled Number of Participants With Severity of Photodamage and is assessed at Week 20. The registry says that severity was assessed with the Griffiths photo numeric scale, which ranges from 0 (minimum) to 8 (maximum), with a higher score indicating a worse outcome. The stated categories are no damage (0), mild damage (1-3), moderate damage (4-6), and severe damage (7-8).

This scale is used to describe the visible severity of cutaneous photodamage in an organized way. A standardized scale can make assessments more consistent than an unstructured description and can represent levels of severity that matter to the study question. It also allows the endpoint to distinguish degrees of damage rather than treating every participant’s appearance as equivalent.

The registry’s endpoint title refers to a number of participants, while its description gives a graded scale. To interpret a count-based endpoint, readers need to know which scale categories were counted, how scores were summarized, and how the Metvix and vehicle observations were compared. Those details and the Week 20 outcome values are not reported in the registry record. The posted record therefore identifies the construct and assessment scale, but it does not permit reconstruction of a category-specific comparison or an estimate of treatment effect.

The stated population is the ITT population, defined in the registry as all enrolled and randomized participants. The record also says that the number analyzed for the outcome means participants evaluable for that outcome, but it does not report how many were evaluable.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The statistical methods used for the primary endpoint are not reported in the registry record. The following concepts explain what would be relevant to interpreting this design; they are general statistical explanations, not descriptions of analyses confirmed to have been used.

How can a half-face comparison be analyzed?

When each participant receives Metvix cream on one half-face and vehicle on the other, the two observations from a participant are naturally linked. General statistical methods for paired data account for that linkage. They compare the treatment observations within participants, rather than acting as if each side came from an unrelated person. This can reduce the influence of characteristics shared by both sides, but a paired analysis still needs to reflect the way the outcome is measured and summarized.

The registry describes a severity scale with ordered categories. A statistical analysis could preserve the order of severity categories, or it could use a prespecified grouping or summary. These choices answer different questions. Treating categories as ordered uses their ranking; counting participants within categories answers questions about the distribution across those categories. The registry does not state which approach was prespecified or used, nor does it give category-specific counts. No particular method should be attributed to the trial on the basis of the scale description alone.

What does a confidence interval contribute?

In general, a confidence interval communicates statistical uncertainty around an estimated effect. It makes the range of estimates compatible with the data more visible than a point estimate alone. Interpretation depends on the endpoint, the analysis, and the interval’s assumptions. A narrow interval generally indicates greater precision than a broad interval, while neither width nor statistical significance by itself establishes clinical importance. No primary endpoint estimate or confidence interval is reported in the registry record, so the precision of the trial’s primary comparison cannot be evaluated.

A p-value, when reported, addresses how compatible the observed data are with a specified null model under the analysis assumptions. It is not the probability that a treatment works, and it does not describe the size of an effect. A p-value should be interpreted alongside an effect estimate and its uncertainty. The registry record does not report a primary endpoint p-value or an analysis from which one could be assessed.

Why do the exposure-duration groups matter?

The treatment descriptions distinguish 1 hour, 2 hour, and 3 hour application groups. Analysis across multiple groups can involve more than one comparison, and interpretation depends on which comparisons were planned and how they were handled. The registry does not report a statistical plan specifying comparisons among the groups, whether exposure duration was a primary focus, or whether any adjustment for multiple comparisons was used. The group descriptions alone do not establish a dose-response analysis or a particular hypothesis test.

Multiplicity is a general concern when many outcomes, time points, groups, or comparisons are examined. If a study conducts multiple tests, the chance of at least one apparently unusual result can increase unless the analysis plan addresses that issue. Appropriate interpretation depends on the tests that were planned and the inferential framework used. The registry lists 13 outcome measures and reports no analysis records, but does not describe a multiplicity strategy. It is therefore not possible to determine how any multiplicity was handled.

What can planning assumptions tell readers?

The registry includes a planning illustration based on the observed effect, with a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. It describes the effect to detect as a stated fraction of the observed effect and distinguishes participant-per-arm illustrations from total event counts for time-to-event outcomes. These are planning assumptions, not evidence that the trial was designed with those assumptions. The registry does not report the trial’s own sample-size justification. Planning illustrations should not be interpreted as observed power, and they cannot supply missing outcome results.

More generally, a sample-size calculation depends on the anticipated effect, variability or event frequency, significance level, desired power, allocation, and analysis method. If a calculation is anchored to an observed effect, it is an illustration of a future planning scenario, not an independent confirmation of the observed effect. Here, the registry’s stated assumptions do not resolve the absence of primary outcome estimates or reveal the design rationale used when the study was planned.

How should analysis populations be understood?

An ITT population ordinarily refers to participants analyzed according to their randomized assignment, preserving the comparison created by randomization. The registry defines this study’s ITT population as all enrolled and randomized participants. It also says that the number analyzed for this outcome refers to participants evaluable for the measure. These descriptions do not establish how missing outcomes were handled or whether the analyzed set included everyone in the ITT definition. The number evaluable and the handling of missing assessments are not reported in the registry record.

Any statistical result would also depend on the measurement process and masking. Masking may help limit some sources of expectation-related bias, but the record does not identify who was masked or describe procedures. The scale assessment method, assessor training, and handling of disagreements are not reported. These details would matter when judging how consistently severity was measured, but they cannot be inferred from the recorded triple-masking label.

10. Multiplicity, Missing Data and Analysis Populations

The registry record does not report a multiplicity plan. It lists 13 outcome measures, and the primary outcome description identifies an assessment at Week 20. The record does not specify which outcomes were confirmatory, how comparisons across the 1 hour, 2 hour, and 3 hour groups were planned, or whether any adjustment was made for multiple testing. Without the prespecified analysis strategy and the results, the effect of multiplicity on interpretation cannot be assessed.

The record defines the ITT population as all enrolled and randomized participants. It also describes the analyzed number for the primary outcome as the participants evaluable for that outcome. The number evaluable is not reported, and there is no account of missing Week 20 assessments, reasons for missingness, or methods used to address missing data. These omissions mean readers cannot determine whether the endpoint analysis included the full ITT population or how incomplete assessments affected the result.

The registry does not report an analysis plan, interim analyses, or statistical methods for the primary endpoint. It also gives no primary endpoint estimates or inferential results. Therefore, there is no basis in the posted record to evaluate the prespecified status of analyses, any exclusions, or the handling of multiple outcomes. These are reporting gaps, not proof that a particular method was or was not used outside the registry record.

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: crohn's disease (11.1%), glioma (9.1%).

The registry lists serious adverse event counts separately for the three exposure-duration groups. In the 1 hour group, 11 participants were at risk and 1 was reported as affected; in the 2 hour group, 9 were at risk and 1 was affected; in the 3 hour group, 12 were at risk and 0 were affected. Deaths were recorded as 0 in each group. For other adverse events, the corresponding at-risk counts were 11, 9, and 12, with 1, 3, and 8 affected, respectively.

These are counts in the registry, not a statistical comparison. The affected counts do not show whether an event was caused by Metvix, vehicle, red-light exposure, or another factor. The half-face treatment descriptions also mean that these group-level safety counts should not be read as a direct comparison of adverse events by treated side. The registry does not report event-level timing, severity beyond the serious classification, attribution, or a comparative safety analysis.

The registry lists Crohn's disease at 11.1% and Glioma at 9.1% among the top serious terms. The record does not explain the denominators or detailed context for those percentages in the information available. They should therefore be read as reported terms and percentages, not as evidence of a treatment-related pattern or as a basis for estimating risk.

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

The trial record describes a randomized Phase 2 study of Metvix PDT and vehicle in participants with photoaged skin. It identifies the treatment schedule, the three application-duration groups, a Week 20 photodamage assessment, and a scale intended to grade severity. It also reports limited adverse-event counts. These registry entries establish the study’s scope and the kind of question it sought to answer.

The record does not show the primary outcome values, category counts, treatment comparison, confidence interval, or p-value. It therefore does not establish whether photodamage severity differed between Metvix and vehicle, how large any difference might have been, or how precisely it was estimated. No conclusion about efficacy or lack of efficacy can be drawn from the registry information alone.

The recorded counts of serious and other adverse events describe what was entered in the registry for each exposure-duration group. They do not establish causation, and they are not accompanied by a statistical comparison or detailed event context. Likewise, the listed serious terms and percentages should not be interpreted as a treatment effect.

The study’s enrollment of 32 participants and completed status are not substitutes for reported results. The registry also does not provide enough information to assess missing outcome data, the analysis population actually used, or the handling of multiple outcomes and comparisons. Those limitations constrain both the strength and the precision of any interpretation.

In short, the posted record supports a description of the research question and trial setup, but not a conclusion about what the primary endpoint showed. A reader needs the outcome data and analysis details to judge the direction, magnitude, uncertainty, and relevance of the findings.

13. Why This Trial Matters Statistically

This trial raises several statistical issues that are useful in reading clinical research. The half-face comparison creates a within-person structure: the two sides of the face belong to the same participant and are not independent observations. A statistical analysis that accounts for pairing can answer the treatment contrast more appropriately than an analysis that ignores the relationship. The registry describes the structure but does not report the method used to analyze it.

The endpoint is based on an ordered severity scale. A scale can retain clinically meaningful gradations, but analysis choices determine whether the result describes score distributions, category counts, or another summary. The registry gives the scale’s range and severity bands, yet does not report how the primary result was summarized. This makes the endpoint definition clearer than the statistical estimand: the precise quantity intended to be compared is not reported.

The three exposure-duration groups and the registry’s 13 outcome measures also make prespecification and multiplicity relevant. Without a reported statistical plan, readers cannot distinguish planned primary comparisons from additional analyses or determine how multiple tests were treated. The lack of posted analyses means this is not merely a matter of interpreting a borderline result; no primary comparison is available to evaluate.

Finally, the registry distinguishes the ITT population from participants evaluable for the endpoint, but does not give the evaluable count or missing-data approach. This illustrates why population definitions and outcome completeness matter: a randomized study’s interpretation depends not only on who entered the trial, but also on who contributed usable endpoint data and how incomplete observations were handled. These features are central to judging both bias and precision.

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 primary limitation is that the registry record does not report the Week 20 primary outcome results. There are no severity-category counts, treatment effect estimates, confidence intervals, or p-values. As a result, neither the direction nor the magnitude and precision of the primary comparison can be assessed.

Although the registry describes the endpoint scale and identifies an ITT population, it does not report the number evaluable for the endpoint or explain how missing data were handled. It also does not report whether the primary analysis included all randomized participants or only participants with evaluable assessments. This limits assessment of possible bias related to incomplete outcome data.

The registry does not describe the statistical analysis, including how the paired half-face observations were handled, how severity scores were summarized, or how the 1 hour, 2 hour, and 3 hour groups were compared. The strategy for multiple outcome measures or comparisons is also not reported. The stated planning illustration is not the trial’s sample-size justification, which is not reported in the registry record.

Some intervention descriptions are incomplete, including the description for the 1 hour group. The registry also does not specify treatment-side allocation procedures, who was masked, or how masking was implemented. Safety reporting gives group counts and selected serious-event terms, but does not provide detailed event context, attribution, or a comparative analysis. These limitations restrict interpretation of both the intended outcome and the adverse-event information.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Comparison of Metvix Photodynamic Therapy (PDT) With Its Vehicle in the Treatment of Photoaged Skin — NCT00437320.
• Registry record last updated 2024-05-31; status last verified 2023-12.
• Results first posted 2024-05-31.
• 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

This completed, randomized Phase 2 trial enrolled 32 participants with photoaged skin. It compared Metvix cream at 160 mg/g with vehicle in half-face treatment descriptions and included 1 hour, 2 hour, and 3 hour application groups. Applications were described at Baseline, Weeks 4 and 8, with red-light exposure. The primary endpoint assessed photodamage severity at Week 20 using the Griffiths photo numeric scale, ranging from 0 to 8.

The registry identifies triple masking and a parallel model. It defines the ITT population as all enrolled and randomized participants, while noting that the number analyzed for the endpoint represents participants evaluable for it. The evaluable count is not reported. The record lists serious and other adverse-event counts by duration group and records no deaths in those groups.

Primary outcome values, statistical analyses, missing-data methods, multiplicity handling, and the trial’s sample-size justification are not reported in the registry record. The posted information therefore describes the study design and intended assessment, but does not support an estimate or conclusion about the primary outcome.