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-4 was a randomized, open-label, parallel phase 2 trial studying a tailored management strategy for patients with locally advanced rectal carcinoma. The registry identifies 150 participants, four arms, and an R0 resection rate as the primary endpoint, assessed within 15 days after surgery.
| Feature | GRECCAR-4 |
|---|---|
| Phase | Phase 2 |
| Population | Patients with locally advanced malignant neoplasm and rectal carcinoma |
| Design | Randomized, parallel, unmasked |
| Allocation | Randomized |
| Primary purpose | Treatment |
| Enrollment | 150 |
| Number of arms | 4 |
| Status | Completed |
| Start date | 2011-05 |
| Primary completion date | 2014-09 |
| Lead sponsor | Institut du Cancer de Montpellier - Val d'Aurelle |
| ClinicalTrials.gov | NCT01333709 |
2. Clinical Question
The registry describes GRECCAR-4 as a multicenter phase 2 trial of a tailored strategy for locally advanced rectal carcinoma. Its primary statistical question is framed around the feasibility of achieving a 90% R0 resection rate across all arms, with R0 resection assessed within 15 days after surgery.
Population
The registry identifies locally advanced malignant neoplasm and rectal carcinoma as the conditions under study.
Intervention strategy
The registered intervention components include induction trichemotherapy using the FOLFIRINOX regimen, early tumor response evaluation by MRI volumetry, radiochemotherapy with Cap 50, radiochemotherapy with Cap 60, and radical proctectomy with total mesorectal excision.
Comparator
The registry identifies four randomized arms but does not specify a single comparator arm in the record summarized here.
Primary question
Can a tailored management strategy achieve the registry's target of a 90% R0 resection rate across all arms?
3. Trial Design
Registered intervention components
| Registered intervention | Type |
|---|---|
| Induction trichemotherapy - FOLFIRINOX regimen | Drug |
| Early tumor response evaluation by MRI volumetry | Other |
| Radiochemotherapy Cap 50 | Radiation |
| Radiochemotherapy Cap 60 | Radiation |
| Radical proctectomy with total mesorectal excision | Procedure |
The combination of randomized allocation, four arms, MRI-based early response evaluation, preoperative treatment components, and surgical assessment makes the design a natural setting for a tailored-management question. Statistically, however, the key distinction is between the design structure and the primary estimand: the registry's primary endpoint is a resection proportion measured after surgery, not a time-to-event endpoint.
4. Endpoints
| Endpoint | Registry definition | Time frame |
|---|---|---|
| Ro resection rate | To confirm the feasibility of a tailored management with a 90% R0 resection rate achieved for all arms. | Within 15 days after surgery |
The registry identifies one registered primary endpoint. The endpoint is a rate, so its statistical structure differs from a continuous measurement such as tumor volume and from a time-to-event outcome such as survival.
5. Statistical Methodology
The primary endpoint is a binary patient-level outcome
R0 resection status can be represented for each participant as either having achieved the endpoint or not having achieved it. Once every eligible participant has a binary outcome, the primary endpoint can be summarized as a proportion:
Here, x represents the number of participants achieving an R0 resection and n represents the relevant number of participants evaluated for the endpoint.
This formulation is important because the primary endpoint is not naturally analyzed with a mean, median, correlation coefficient, or hazard ratio. The central statistical quantity is the proportion of patients achieving the specified surgical outcome.
Confidence intervals for a resection rate
A proportion should generally be accompanied by a confidence interval. For a binomial endpoint, exact or score-based methods can be used depending on the prespecified statistical plan. A confidence interval communicates the precision of the observed proportion rather than the probability that the true rate is inside the particular interval after the data have been observed.
The parameter p represents the underlying probability of achieving an R0 resection under the population and treatment strategy being studied.
Comparison with the 90% feasibility target
The registry's primary objective is to confirm feasibility with a 90% R0 resection rate achieved for all arms. A statistical analysis of this objective would therefore need to distinguish between the observed R0 proportion and the prespecified 90% target.
If the protocol frames 90% as a formal hypothesis-test benchmark, a one-sample binomial framework or an equivalent confidence-interval decision rule would be appropriate. If 90% is instead a descriptive feasibility threshold, the emphasis would be on the estimated rate and its precision. The registry wording alone does not specify which of these inferential conventions was used.
6. Statistical Methods Explained
What makes the R0 resection rate a binary endpoint?
For each participant, the endpoint can be reduced to whether the specified surgical outcome was achieved. That produces a yes/no outcome that can be summarized as a proportion. This is fundamentally different from measuring a continuous quantity such as tumor volume or analyzing the time until an event occurs.
Why is a confidence interval useful for the R0 rate?
An observed percentage from a finite sample is an estimate of an underlying probability. The confidence interval describes statistical uncertainty around that estimate. A rate of 90% based on a relatively small number of observations is not as precise as the same observed rate based on a much larger number of observations.
Why does the 90% target matter?
The 90% figure gives the primary endpoint a concrete feasibility benchmark. Without a benchmark, an R0 rate is primarily descriptive. With a prespecified target, the analysis can ask whether the observed performance is sufficiently compatible with the desired feasibility level.
Why should the four arms not automatically be pooled?
The registry identifies four randomized arms. Pooling those arms would change the statistical question and could conceal differences between strategies. If the stated objective is to demonstrate a 90% R0 rate for all arms, each arm's rate becomes relevant rather than only the overall rate.
Why does the timing of the endpoint matter?
The endpoint is assessed within 15 days after surgery. That defines the window in which the outcome is attributed to the primary analysis. A consistent endpoint window helps prevent different participants from being evaluated under materially different definitions of the outcome.
Why is this not a Kaplan-Meier problem?
The registered primary endpoint is a surgical resection rate measured within a defined postoperative window. There is no registered time-to-event definition for this endpoint. Kaplan-Meier estimation is designed for outcomes where the timing of an event and censoring are central to the analysis, whereas the primary GRECCAR-4 endpoint is a binary proportion.
7. Planned Analysis
The ClinicalTrials.gov record identifies Ro resection rate as the primary endpoint, with assessment within 15 days after surgery. The stated objective is to confirm the feasibility of a tailored management strategy with a 90% R0 resection rate achieved for all arms.
For an endpoint of this type, the principal analysis would ordinarily begin with the number and proportion of participants achieving an R0 resection in each randomized arm. Because the registry identifies four arms, an arm-specific presentation is particularly important when the objective is expressed as a rate achieved for all arms.
| Planned statistical element | Purpose |
|---|---|
| R0 resection count | Identify the number of participants meeting the endpoint definition. |
| R0 resection rate | Estimate the proportion achieving the surgical endpoint. |
| Confidence interval | Quantify uncertainty around each estimated proportion. |
| 90% benchmark | Provide the feasibility target against which the observed rate can be interpreted. |
| Arm-specific assessment | Evaluate the stated objective that the target rate be achieved for all arms. |
The appropriate inferential details would depend on the prespecified statistical analysis plan, including the exact analysis population, handling of participants without an evaluable surgical outcome, and whether the 90% benchmark was to be evaluated with a formal hypothesis test or a confidence-interval criterion. Those details are not specified in the registry record.
8. Analysis Population and Denominator Considerations
For a surgical binary endpoint, the denominator is a central statistical issue. A reported R0 rate can differ depending on whether the denominator is all randomized participants, all participants undergoing surgery, or another prespecified analysis population.
Randomized denominator
Using all randomized participants preserves the original randomized population but can require a rule for participants who do not reach surgery or do not have an evaluable postoperative outcome.
Surgery-based denominator
Restricting the denominator to participants who undergo surgery can describe surgical performance among those reaching the operation, but it may condition the analysis on an event occurring after randomization.
Missing endpoint status
Participants without a determinable R0 status require a prespecified handling rule. The choice can affect the estimated rate, especially when the number of missing outcomes is not negligible.
Arm-specific precision
Because the study has four randomized arms, each arm's estimate can be less precise than an overall estimate based on all participants combined.
The registry establishes the enrollment of 150 participants and the existence of four arms, but it does not report the number of participants assigned to each arm or the number with an evaluable R0 outcome.
9. Understanding the 90% Target
A 90% target means that the desired feasibility level corresponds to nine successful R0 resections for every ten evaluated participants, if the observed rate were exactly 90%.
The target itself is not an observed treatment effect. It is a benchmark against which the estimated surgical success rate can be evaluated.
The 90% figure does not establish that 90% of participants actually achieved R0 resection. It describes the feasibility level that the registry says the trial was intended to confirm.
An observed rate near 90% can have substantial statistical uncertainty when the number of evaluable participants is limited. Conversely, an estimate farther from 90% may still require an appropriate uncertainty assessment before a formal conclusion is drawn.
10. Four-Arm Design and Statistical Interpretation
The four-arm randomized structure affects how the primary endpoint should be interpreted. A single overall R0 proportion would combine information across the treatment strategies and could obscure whether the feasibility objective was met consistently across the individual arms.
| Design feature | Statistical implication |
|---|---|
| Randomized allocation | Creates the basis for comparing randomized strategies while reducing allocation-related confounding. |
| Four arms | Creates multiple arm-specific endpoint estimates rather than a single two-group comparison. |
| Parallel design | Participants remain associated with their randomized arm for the primary comparison rather than serving as their own controls. |
| No masking | The trial is open-label, so treatment assignment is not concealed from participants or investigators after allocation. |
| R0 rate as primary endpoint | The principal statistical quantity is a proportion rather than a hazard ratio or mean difference. |
11. Randomization and Causal Interpretation
Randomization is important because it establishes the treatment groups before subsequent clinical events occur. In principle, this allows differences in outcomes between randomized groups to be interpreted as differences associated with the assigned strategies rather than simply differences in pre-treatment patient characteristics.
That causal interpretation is strongest when the prespecified analysis remains aligned with randomized assignment and when post-randomization exclusions are handled according to a clearly defined statistical plan.
For GRECCAR-4, the registry identifies randomized allocation and a parallel design, but it does not provide the randomization ratio, allocation sequence, stratification factors, or detailed analysis-population definitions.
12. MRI Volumetry and Tailored Treatment
Early tumor response evaluation by MRI volumetry is registered as an intervention component. Statistically, this is notable because an early measurement can be used to distinguish subsequent treatment pathways in a tailored strategy.
When an intermediate response assessment influences later management, the resulting trial structure can be more complicated than a simple two-arm comparison. The response measurement may occur after randomization and can therefore become a post-randomization variable. Statistical interpretation should distinguish the effect of the original randomized strategy from associations involving subsequent treatment decisions.
13. Surgical Endpoint Interpretation
R0 resection is a surgical outcome rather than a conventional symptom score or laboratory measurement. The statistical analysis therefore needs to preserve the endpoint's binary nature while respecting the clinical timing of the assessment.
Endpoint
The registry calls the endpoint “Ro resection rate” and describes the objective as a 90% R0 resection rate achieved for all arms.
Assessment window
The registered time frame is within 15 days after surgery.
Statistical scale
The natural summary is a proportion, accompanied by an appropriate measure of uncertainty.
Clinical interpretation
The endpoint addresses whether the specified surgical result was achieved, not survival or recurrence after surgery.
14. Why a p-Value Alone Would Be Insufficient
If a formal hypothesis test were used to compare an observed R0 rate with a 90% benchmark, the resulting p-value would answer a narrow question about compatibility with the null hypothesis under the specified testing framework.
It would not describe the magnitude of the observed R0 rate, the uncertainty around the rate, or the clinical consequences of the result. Those questions require the estimated proportion and its confidence interval.
The estimate describes what was observed, the confidence interval describes precision, and the benchmark defines the feasibility level against which the estimate is interpreted.
15. Multiplicity in a Four-Arm Trial
A four-arm design can create several possible statistical comparisons. The registry's primary endpoint wording, however, is not expressed as a hierarchy of pairwise treatment comparisons. It states a feasibility objective involving a 90% R0 resection rate achieved for all arms.
This distinction matters because testing several pairwise hypotheses can increase the probability of a false-positive result if multiplicity is not addressed. Conversely, an arm-specific feasibility objective may call for a different inferential framework than a collection of pairwise superiority tests.
| Question | Statistical issue |
|---|---|
| Did an individual arm reach the target? | Arm-specific estimation and comparison with the 90% benchmark. |
| Did all four arms reach the target? | A joint interpretation is needed rather than relying on only the pooled rate. |
| Are two arms different? | A comparative hypothesis requires a prespecified contrast and appropriate multiplicity considerations. |
| What is the overall feasibility rate? | A pooled estimate answers a different question from an arm-specific feasibility assessment. |
The registry does not report a multiplicity strategy, alpha allocation, or a hierarchy of pairwise comparisons for the primary endpoint.
16. Interim Analysis, Bayesian Methods, and Missing Data
The registry record summarized here does not report an interim statistical analysis plan, Bayesian methodology, or a specific missing-data or imputation procedure for the primary endpoint.
Interim analysis
No interim-analysis methodology is specified in the registry record.
Bayesian methods
No Bayesian analysis is specified for the registered primary endpoint.
Missing data
The registry does not specify how missing R0 resection assessments are handled.
Imputation
No imputation method for the primary endpoint is specified in the registry record.
These omissions are statistically important because the treatment of missing surgical outcomes can change the denominator and therefore the estimated R0 resection rate. A formal analysis should follow the prespecified statistical analysis plan if such a document is available.
17. What Would a Complete Primary Analysis Report?
A statistically complete report of the registered primary endpoint would ordinarily make several elements visible to the reader rather than presenting only a single percentage.
| Reporting element | Why it matters |
|---|---|
| Number evaluated | Defines the denominator behind the reported rate. |
| Number with R0 resection | Shows the event count underlying the proportion. |
| R0 resection rate | Provides the primary point estimate. |
| Confidence interval | Shows statistical precision. |
| Arm-specific estimates | Allows the four-arm structure to be understood. |
| Handling of unevaluable participants | Clarifies how the denominator was constructed. |
| Benchmark decision rule | Shows how the 90% feasibility objective was formally evaluated. |
The ClinicalTrials.gov record does not post the corresponding statistical results for these elements.
18. Limitations
- No posted statistical analyses: the registry does not post a statistical analysis for the registered primary endpoint.
- No observed R0 rate: the registry does not report an observed R0 resection proportion for the four arms.
- No arm sizes: although enrollment is 150 and four arms are identified, the registry record does not provide the number assigned to each arm.
- Unspecified analysis population: the registry does not define the denominator used for the R0 resection rate.
- Unspecified missing-data handling: the registry does not describe how participants without an evaluable R0 outcome are treated statistically.
- Unspecified inferential rule: the registry states a 90% feasibility target but does not identify whether it was evaluated using a formal hypothesis test, a confidence-interval criterion, or another rule.
- Four-arm multiplicity: the registry does not describe a multiplicity strategy for possible comparisons among the four arms.
- Limited endpoint scope: the registered primary endpoint concerns surgical resection status within 15 days after surgery and does not itself measure long-term survival or recurrence.
- Open-label design: masking is listed as none, so treatment assignment is not blinded.
19. Why This Trial Matters Statistically
GRECCAR-4 is a useful teaching case because it illustrates a different statistical structure from the many randomized oncology trials whose primary endpoints are survival outcomes. Here, the registry-defined primary endpoint is a binary surgical outcome with a prespecified feasibility target.
| Concept | How it appears in GRECCAR-4 |
|---|---|
| Randomization | The trial uses randomized allocation. |
| Parallel design | The registry identifies a parallel design model. |
| Four-arm structure | Four randomized arms are registered. |
| Binary endpoint | R0 resection status can be represented as achievement or non-achievement of the surgical outcome. |
| Proportion estimation | The primary endpoint is an R0 resection rate. |
| Feasibility benchmark | The registry specifies a 90% R0 resection rate as the target. |
| Endpoint timing | The primary endpoint is assessed within 15 days after surgery. |
| Denominator selection | The analysis must define which participants contribute to the rate. |
| Missing outcomes | Participants without an evaluable surgical outcome require a prespecified handling rule. |
| Open-label treatment | Masking is listed as none. |
| Tailored treatment | Early tumor response evaluation by MRI volumetry is registered as part of the intervention strategy. |
20. Statistical Interpretation of a Feasibility Endpoint
A feasibility endpoint should be interpreted differently from a conventional superiority endpoint. The key question is not simply whether one treatment group has a larger observed percentage than another. Instead, the analysis asks whether the observed performance is sufficiently consistent with a predefined level of feasibility.
For GRECCAR-4, the registry identifies 90% as that level. A rigorous interpretation would therefore place the observed R0 rate, its uncertainty, and the prespecified decision rule side by side.
The R0 resection rate is the observed proportion of participants meeting the surgical endpoint within the registered assessment window.
The confidence interval indicates how precisely the underlying R0 probability is estimated from the analyzed participants.
The 90% figure provides the feasibility level identified by the registry. It is not itself an estimate of what occurred in the trial.
Because the feasibility objective is described as applying to all arms, arm-specific estimates are essential to understanding whether the stated objective was met consistently.
21. Clinical Interpretation vs Statistical Interpretation
Statistical interpretation
The primary endpoint is a binary surgical outcome summarized as a rate and evaluated against a 90% feasibility target. The appropriate analysis depends on the prespecified denominator, uncertainty method, and decision rule.
Clinical interpretation
The endpoint addresses whether the specified R0 surgical outcome was achieved within 15 days after surgery. It should not be interpreted as a direct measure of long-term survival, recurrence, or overall treatment benefit.
22. Sources
- ClinicalTrials.gov: NCT01333709 — GRECCAR-4.
Continue through the Clinical Biostats clinical-trial library
Explore additional clinical trial statistical analyses and the broader collection of biostatistics tutorials and statistical tools.
23. Record Summary
GRECCAR-4 is a randomized phase 2 trial with 150 participants and four parallel arms evaluating a tailored strategy for locally advanced rectal carcinoma. Its registered primary endpoint is the Ro resection rate, assessed within 15 days after surgery, with the stated objective of confirming a 90% R0 resection rate achieved for all arms.
From a statistical perspective, the trial is centered on a binary surgical endpoint rather than a time-to-event outcome. The key analytical issues are therefore the arm-specific R0 proportions, the denominator used for each estimate, statistical uncertainty around those proportions, treatment of unevaluable outcomes, and the prespecified rule for evaluating the 90% feasibility benchmark.