This page provides an independent statistical analysis and educational interpretation of publicly reported results. ClinicalTrials.gov provides the official trial registry record.
1. Trial at a Glance
GRECCAR 2 was a completed randomized phase 3 trial evaluating local rectal excision versus total mesorectal excision in patients with rectal neoplasms. The registry identifies a single primary composite endpoint assessed at 24 months.
| Feature | GRECCAR 2 |
|---|---|
| Trial acronym | GRECCAR 2 |
| Phase | Phase 3 |
| Condition | Rectal Neoplasms |
| Allocation | Randomized |
| Design model | Parallel |
| Masking | None |
| Primary purpose | Supportive care |
| Enrollment | 148 |
| Number of arms | 2 |
| Start date | 2007-03-05 |
| Primary completion | 2014-12 |
| Lead sponsor | University Hospital, Bordeaux |
| Sponsor type | OTHER |
| Registry identifier | NCT00427375 |
2. Clinical Question
The registry describes GRECCAR 2 as a randomized phase 3 comparison of two surgical approaches for rectal neoplasms: local rectal excision and total mesorectal excision. Its primary question is expressed through the comparison of the proportion of patients presenting at least one component of a four-component composite outcome at 24 months.
Population
Patients enrolled in the GRECCAR 2 trial with the registry-listed condition of rectal neoplasms.
Intervention
Local rectal excision.
Comparator
Total mesorectal excision.
Primary question
How does the proportion presenting at least one component of the specified composite outcome at 24 months compare between the two randomized treatment arms?
The registry does not provide additional eligibility criteria or baseline clinical characteristics in the information represented here. Consequently, the population can be described at the level of the registered condition rather than by more specific disease stage, response status, or demographic criteria.
3. Trial Design
Local rectal excision
- Intervention type: procedure
- Registered intervention: local rectal excision
Total mesorectal excision
- Comparator type: procedure
- Registered intervention: total mesorectal excision
Why the randomized parallel structure matters
Randomization creates the framework for comparing outcomes between the two procedures. In a parallel design, each participant contributes to one randomized treatment group, and the primary comparison is made between those groups over the prespecified follow-up period.
The absence of masking is also important statistically. Because the procedures are not described as masked, assessment of outcomes that contain clinical or subjective components can potentially be influenced by knowledge of treatment assignment. The extent of that issue depends on how each component of the composite outcome was defined and assessed; the registry information available here does not provide those additional assessment details.
4. Endpoints
| Endpoint | Registry definition | Time frame |
|---|---|---|
| Primary endpoint | Compare the proportion of patients presenting at least 1 component of the composite outcome (4 components: death, recurrence, major morbidity and severe after effects) at 2 years after | 24 months |
The composite endpoint
The primary endpoint combines four distinct components: death, recurrence, major morbidity, and severe after effects. A patient presenting at least one component is therefore counted according to the composite endpoint definition even if the patient does not experience the other components.
Death
One of the four components of the registered composite outcome.
Recurrence
One of the four components of the registered composite outcome.
Major morbidity
One of the four components of the registered composite outcome.
Severe after effects
One of the four components of the registered composite outcome.
The registry wording identifies the endpoint as a comparison of proportions at 24 months rather than a time-to-first-event endpoint. That distinction is important: the primary endpoint is framed around whether patients present at least one component by the specified assessment time, rather than reporting a hazard ratio over continuous follow-up.
5. Planned Analysis
The ClinicalTrials.gov record identifies the primary endpoint but does not post a formal statistical analysis or numerical primary-endpoint result. The endpoint is a binary composite outcome assessed at 24 months, so a conventional analysis would compare the proportion of patients with at least one component of the composite outcome between the two randomized groups.
Primary estimand concept
Compare the proportion of patients presenting at least one component of the four-component composite outcome between local rectal excision and total mesorectal excision.
For a binary endpoint of this type, several measures can describe the between-group effect. The risk difference compares the two proportions directly, the risk ratio expresses one proportion relative to the other, and an odds ratio compares the corresponding odds. A confidence interval around the chosen effect measure provides information about its statistical precision.
The risk difference expresses the absolute difference between the two 24-month proportions. A value near zero indicates similar observed proportions; its interpretation should be accompanied by an uncertainty interval rather than considered from the point estimate alone.
How a primary comparison would typically be evaluated
A binary outcome can be compared using a two-group proportion test such as a chi-square test when its assumptions are appropriate, or an exact method when sparse cell counts make an asymptotic approximation unreliable. Regression-based approaches can also estimate an adjusted treatment effect when prespecified covariates are appropriate.
For GRECCAR 2 specifically, the registry information presented here does not identify which of these methods was used. The appropriate statistical interpretation therefore begins with the endpoint's structure—two randomized groups and a binary composite outcome at 24 months—rather than assigning an unreported test to the study.
6. Statistical Methods Explained
Why use a proportion for this primary endpoint?
The endpoint is explicitly defined as a comparison of the proportion of patients presenting at least one component of the composite outcome at 24 months. This creates a binary patient-level outcome for the primary comparison: the patient either presents at least one listed component by the assessment time or does not.
What does a composite endpoint mean here?
A composite endpoint combines multiple clinically distinct outcomes into one analysis. In GRECCAR 2, the four components are death, recurrence, major morbidity, and severe after effects. The primary endpoint therefore captures whether at least one of these components occurs rather than treating each component as a separate primary endpoint.
Why can composite endpoints be useful?
Combining clinically relevant events can increase the number of patients contributing an endpoint event and can capture a broader definition of an unfavorable outcome. The tradeoff is interpretational: the individual components may differ in clinical importance, frequency, and susceptibility to treatment effects. A composite result therefore should not automatically be interpreted as showing the same effect on every component.
What is the difference between a risk difference and a risk ratio?
A risk difference is an absolute comparison of proportions, whereas a risk ratio is a relative comparison. For example, if one group had a proportion of 0.30 and another had 0.20, the risk difference would be 0.10 while the risk ratio would be 1.5. These measures answer different questions and can lead to different impressions of the magnitude of an effect.
Why does the 24-month time frame matter?
The primary endpoint is tied to a specific assessment time of 24 months. A proportion at 24 months is not interchangeable with a median time to event or a hazard ratio from a time-to-event analysis. The estimand is anchored to the prespecified time point and to whether at least one component has occurred by that point.
Why should the four components be examined separately when possible?
A composite endpoint can conceal differences among its components. For example, a treatment effect on recurrence could contribute to the overall composite without implying an identical effect on major morbidity or death. Component-level results can therefore help explain what is driving the composite, although the registry information represented here does not provide those component-specific results.
7. Interpreting the Primary Endpoint
The central quantity is the between-group difference in the proportion of patients presenting at least one of the four registered components at 24 months. This is an absolute risk comparison at a defined time point, not inherently a hazard ratio or median survival comparison.
A patient is counted as having met the composite if at least one of death, recurrence, major morbidity, or severe after effects is present according to the endpoint definition. The composite is therefore broader than any single one of its four components.
A composite endpoint should not be read as though all four components occurred with equal frequency or clinical importance. The overall proportion alone cannot establish which component contributes most strongly to the result.
A point estimate describes the observed between-group difference, but a confidence interval would describe statistical precision around that estimate. A narrow interval indicates greater precision than a wide interval under the corresponding statistical model and sampling framework.
If a formal hypothesis test is performed, its p-value addresses compatibility with a specified null hypothesis under the statistical model. It does not quantify the clinical magnitude of the difference. The effect estimate and its confidence interval are needed to describe magnitude and precision.
8. Limitations
- No posted numerical results: the registry information represented here contains the primary endpoint definition but no posted statistical estimate, confidence interval, or p-value.
- Composite interpretation: the primary outcome combines death, recurrence, major morbidity, and severe after effects. These components can have different clinical meanings and event frequencies.
- Assessment at a fixed time: the registered endpoint is evaluated at 24 months, so it should not automatically be interpreted as a continuous time-to-event analysis.
- No posted statistical method: the registry does not identify the specific hypothesis test, effect measure, confidence-interval method, or regression model used for the primary comparison in the information represented here.
- No masking: the trial is registered as having no masking. For outcomes involving clinical assessment, knowledge of treatment assignment can be a consideration in interpretation.
- Limited population detail: the registry information represented here identifies rectal neoplasms as the condition but does not provide additional eligibility or baseline-characteristic detail.
- No component-level results: the available registry information does not provide numerical results separately for death, recurrence, major morbidity, or severe after effects.
9. Why This Trial Matters Statistically
GRECCAR 2 is a useful teaching example because its primary endpoint illustrates a different statistical structure from a conventional overall-survival or progression-free-survival analysis. The registry specifies a randomized comparison of proportions at a fixed time point using a composite endpoint with four clinically distinct components.
| Statistical concept | How it appears in GRECCAR 2 |
|---|---|
| Randomization | The trial uses randomized allocation. |
| Parallel design | The two procedures are evaluated in parallel treatment arms. |
| Binary endpoint | The primary endpoint asks whether a patient presents at least one component of the composite outcome. |
| Composite endpoint | The primary outcome contains four components: death, recurrence, major morbidity and severe after effects. |
| Absolute risk comparison | The registry explicitly describes comparison of proportions. |
| Fixed-time assessment | The registered primary time frame is 24 months. |
| Unmasked trial | The registry identifies masking as none. |
| Interpretability of composites | The overall composite proportion must be distinguished from effects on its individual components. |
10. Trial Timeline
Trial start
The registered study start date is 2007-03-05.
Randomized parallel evaluation
The trial is registered as a phase 3 randomized parallel study with two procedure arms and no masking.
Primary endpoint time frame
The primary endpoint compares the proportion of patients presenting at least one component of the four-component composite outcome at 24 months.
Primary completion
The registered primary completion date is 2014-12.
11. Clinical Question vs Statistical Question
Clinical question
How do local rectal excision and total mesorectal excision compare with respect to the registered composite outcome at 24 months?
Statistical question
Does the proportion of randomized patients presenting at least one component of the composite outcome differ between the two treatment groups at the prespecified 24-month assessment?
Keeping these questions separate helps prevent a common interpretation error. The clinical question concerns the meaning of the outcome and the comparison of procedures. The statistical question concerns how much the observed proportions differ and how precisely that difference is estimated.
12. Safety and the Composite Endpoint
The registered primary endpoint includes major morbidity and severe after effects, but the information represented here does not provide separate safety tables, serious adverse-event counts by arm, or numerical results for those individual components.
This distinction matters because a composite endpoint is not equivalent to a conventional adverse-event summary. The primary endpoint integrates several outcome categories, including death and recurrence, while a safety analysis ordinarily describes adverse events according to defined severity and seriousness categories. Those analyses answer different questions and should not be substituted for one another.
13. Statistical Interpretation of a Two-Arm Proportion Comparison
The risk ratio expresses the 24-month composite-event proportion in one randomized group relative to the other. It is a relative measure and should be interpreted alongside the underlying proportions.
The odds ratio compares odds rather than probabilities. When the outcome is common, the odds ratio can differ materially from the risk ratio, so the two measures should not be treated as interchangeable.
Why absolute proportions should remain visible
Relative measures can be useful for comparing groups, but the underlying 24-month proportions show the absolute frequency of the composite outcome. Reporting both proportions makes the clinical scale of the comparison easier to understand.
Why randomization does not eliminate every source of uncertainty
Randomization provides the basis for a treatment comparison, but the observed difference is still subject to sampling variability. Confidence intervals quantify that uncertainty under the selected statistical framework. In addition, interpretation of a composite endpoint depends on how its individual components behave.
14. What the Registry Establishes
| Question | Registered information |
|---|---|
| Was the study randomized? | Yes. |
| Was it parallel? | Yes. |
| Was masking used? | No. |
| How many patients were enrolled? | 148. |
| How many arms were registered? | 2. |
| What procedures were compared? | Local rectal excision and total mesorectal excision. |
| What was the primary endpoint? | Comparison of the proportion of patients presenting at least 1 component of the four-component composite outcome at 2 years after. |
| What was the primary time frame? | 24 months. |
| Are numerical primary results posted? | No formal statistical analyses are posted in the ClinicalTrials.gov record represented here. |
15. Important Interpretation Issues
- Composite endpoints require component awareness: the overall endpoint combines four different outcomes, so its interpretation should remain tied to the individual components.
- Fixed-time proportion is not a hazard: a 24-month proportion is an absolute time-point measure and should not be translated into a hazard ratio without an appropriate time-to-event analysis.
- Relative and absolute measures differ: risk differences, risk ratios, and odds ratios describe different aspects of the same two-group comparison.
- Unmasked design: knowledge of treatment assignment can matter particularly when endpoint components require clinical assessment.
- Statistical significance and magnitude are different: a p-value, if reported, would address a hypothesis-testing question rather than directly quantify the size or clinical importance of the treatment difference.
- Component effects can differ: an overall composite difference does not establish that each component has the same direction or magnitude of treatment effect.
16. Sources
- ClinicalTrials.gov: NCT00427375 — GRECCAR 2.
- PubMed: PubMed record 34097005.
- PubMed: PubMed record 32043980.
- PubMed: PubMed record 28601342.
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17. Record Summary
GRECCAR 2 is registered as a completed randomized phase 3 parallel trial with 148 enrolled patients and two procedure arms: local rectal excision and total mesorectal excision. Its primary endpoint is a comparison of the proportion of patients presenting at least one component of a composite outcome consisting of death, recurrence, major morbidity and severe after effects at 24 months.
Statistically, the central feature of GRECCAR 2 is therefore a two-group fixed-time comparison of a composite binary outcome. The most natural descriptive framework is to report the 24-month proportions in each randomized group together with an appropriate absolute or relative effect measure and its confidence interval. The composite structure then requires careful consideration of the four individual components rather than treating the overall proportion as a complete description of every clinical outcome.