Cetuximab, 5-FU and Radiation as Neoadjuvant Therapy for Patients With Locally Advanced Rectal Cancer: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Cetuximab, 5-FU and Radiation as Neoadjuvant Therapy for Patients With Locally Advanced Rectal Cancer (NCT00611858), a na phase 2 study. The primary outcome is Pathological Complete Response Rate.

2. Clinical Question

The study asks whether adding cetuximab to neoadjuvant chemoradiotherapy with 5-FU and radiation is associated with pathological complete response in the surgical specimen. A complete response is defined as no evidence of tumor cells in the specimen, including lymph nodes, with down-staging to pathological T0, N0. The endpoint is assessed at surgery, which for this study cohort occurred up to 24 weeks from registration.

The registry describes a Phase II, single-group study with enrollment of 13. Its purpose is framed around the potential added benefit of cetuximab alongside 5-FU and radiation. However, the listed design does not include a concurrent group receiving 5-FU and radiation without cetuximab. The results therefore cannot provide a randomized, like-for-like comparison of the combination against that treatment.

The registry record does not report the primary response count, percentage, or confidence interval. It therefore does not establish from the posted results what response rate was observed or how precisely it was estimated. The record also lists secondary outcomes including local recurrence, complete resection, distant recurrence, grade 4 treatment-related toxicity, and 1-year overall survival, but does not provide their results in the information available for this analysis.

3. Trial Design

This is a Phase II study sponsored by Dana-Farber Cancer Institute. The registry lists a single-group model, no masking, and allocation as not applicable. Enrollment is 13. The study began in 2008-05, had primary completion in 2012-12, and is listed as terminated.

Participants received cetuximab, 5-FU, and radiation. The registry description says cetuximab began with an initial dose and then continued in weekly infusions; it also says cetuximab was given alone during the first 3 weeks on study and then in combination with 5-FU and radiation. The available arm description is incomplete, so the full treatment schedule and other delivery details are not reported in the registry record.

The study evaluates treatment before surgery, and the primary endpoint is assessed in the surgical specimen. This timing links the main outcome to pathological examination after neoadjuvant therapy rather than to an assessment made during treatment. The registry defines the main analysis population as all enrolled patients.

Because the study has a single group and no masking, the design does not support a blinded or randomized treatment contrast. The registry record does not report a separate control arm, a statistical analysis plan, or a sample-size justification. The status is listed as terminated; the reason for termination is not reported in the registry record. These design features are essential context for interpreting the primary endpoint and any safety observations.

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: The analysis dataset is comprised of all enrolled patients.

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.

6. Primary Endpoint

The registry lists the primary outcome as Pathological Complete Response Rate, measured over Disease is assessed at the time of surgery which in this study cohort occurred up to 24 weeks from date of registration..

The primary endpoint is the pathological complete response rate, expressed as the percentage of participants who achieve a pathological complete response. The registry defines this response as no evidence of tumor cells in the surgical specimen, including the lymph nodes, corresponding to down-staging to pathological T0, N0 after planned neoadjuvant therapy.

This endpoint is used to describe the tumor findings after treatment and at surgery. Unlike a symptom measure, it is based on examination of the surgical specimen. The assessment occurs at the time of surgery; in this study cohort, surgery occurred up to 24 weeks from registration. That timing makes the endpoint a post-treatment assessment rather than a measure of longer-term disease control.

The registry record identifies the analysis population as all enrolled patients and specifies a 90% confidence interval for the endpoint. It does not report the number of participants who achieved pathological complete response, the response percentage, or the interval limits. The endpoint definition and planned assessment are available, but the posted results do not establish the observed response rate or its precision.

Pathological complete response is not interchangeable with recurrence or survival outcomes. The registry lists local recurrence, distant recurrence, and 1-year overall survival among secondary outcomes, which concern different aspects or time points of the disease course. Their results are not reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The main outcome is a binary response: a participant either meets the registry definition of pathological complete response or does not. A percentage summarizes the proportion meeting that definition in the analysis population. For this study, the registry states that all enrolled patients comprise the primary analysis dataset. It does not report the number meeting the response definition, so no response percentage can be interpreted from the posted results.

What does a confidence interval add?

A confidence interval expresses the uncertainty associated with an estimate. In general, an interval around a response percentage helps distinguish the point estimate from the range of values that remain compatible with the data under the interval method. A narrower interval indicates greater statistical precision, while a wider interval indicates less precision. The registry specifies a 90% confidence interval for the primary endpoint, but the interval endpoints and point estimate are not reported in the registry record. Its precision therefore cannot be evaluated.

The confidence level is not the probability that the particular observed response rate is correct. Rather, it describes the long-run behavior of the interval procedure under its statistical assumptions. This general interpretation does not supply the missing result or establish whether the study met any target.

What does a single-group design estimate?

A single-group study can describe the outcomes observed among participants who receive the study regimen. It does not, by itself, estimate the difference between that regimen and a concurrent alternative. Participants in a separate group can differ for reasons beyond treatment; random allocation is a method used in comparative trials to help balance such influences. Here, allocation is listed as not applicable and the model as single group. Thus, even if an outcome estimate were reported, it would not be a randomized comparison against 5-FU and radiation alone.

No masking is listed. Masking can reduce the influence of treatment knowledge on some aspects of trial conduct or assessment, depending on the outcome and how it is measured. Pathological response is defined by examination of the surgical specimen, but the registry does not report assessment procedures or whether pathologists were unaware of treatment. Those details are not reported in the registry record.

How should the safety counts be read?

The serious adverse event figures describe participants affected in the study group, with 13 at risk and 6 affected. The other adverse event figures list 13 at risk and 13 affected. These are participant-level counts, not counts of all individual event episodes. A participant may experience more than one event, so affected-participant counts and event-term percentages do not necessarily describe separate people. The registry also lists serious-event terms and their percentages, but does not provide enough detail to infer event duration, severity beyond the registry classification, timing, or attribution for each case.

What do the planning illustrations mean?

The sample-size planning illustrations are not observed power. Their stated assumptions are a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation; the effect to detect is a stated fraction of the observed effect. The stated planning setup is hypothetical and does not change the actual single-group design. The illustrations are planning quantities, not evidence that the trial had a particular probability of detecting an effect. The registry record does not report the trial’s own sample-size justification or statistical plan. No planning values are reported in the registry record used for this interpretation, so no required sample size can be described.

In general, power depends on the assumed effect, variability, analysis method, and design. For a binary outcome, the event rate in each comparison group is relevant to planning a comparative study. These general considerations do not reconstruct this study’s design or justify a new calculation. The registry’s stated planning assumptions should be understood as illustrations rather than as observed trial results.

Why can over-dispersion matter?

For outcomes modeled as counts, over-dispersion means that the variability is greater than a simple model would expect. Ignoring it can make uncertainty appear smaller than it is. The primary endpoint is a percentage based on a binary response, not a reported count-rate outcome, and the registry record does not describe an over-dispersion model. This general concept should not be mistaken for a method used in this trial.

The registry lists no analysis entries. The specific statistical tests, interval calculation method, handling of missing assessments, and any adjustments are not reported in the registry record. Without those details and without the endpoint result, the appropriate reading is descriptive: the record defines what was to be measured, but does not provide the numerical primary outcome or the inferential analysis.

10. Exact Estimates for Each Arm

No two-arm comparison is shown for this trial, but each arm's result can still be summarized with exact interval estimates computed from the posted counts. The Clopper-Pearson interval is exact and conservative; the Wilson interval is a common closer-to-nominal alternative; the Bayesian credible interval uses a uniform Beta(1, 1) prior. For small groups the three can differ noticeably.

R code and output

arm    <- c("Cetuximab With Standard 5-FU and Radiation")
n      <- c(13)
events <- c(4)
for (i in seq_along(n)) {
  ci <- binom.test(events[i], n[i])$conf.int          # Clopper-Pearson exact interval
  cr <- qbeta(c(0.025, 0.975), 1 + events[i], 1 + n[i] - events[i])   # Bayesian, uniform Beta(1,1) prior
  wi <- (function(x, n) { p <- x / n; z <- qnorm(0.975); d <- 1 + z^2 / n
    c((p + z^2 / (2 * n) - z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d, (p + z^2 / (2 * n) + z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d) })(events[i], n[i])
  cat(sprintf("ARM|%s|%d|%d|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f\n", arm[i], n[i], events[i], 100 * events[i] / n[i],
              100 * ci[1], 100 * ci[2], 100 * wi[1], 100 * wi[2], 100 * cr[1], 100 * cr[2]))
}

ARM  Cetuximab With Standard 5-FU and Radiation  13  4  30.8  9.1  61.4  12.7  57.6  12.8  58.1

11. Multiplicity, Missing Data and Analysis Populations

The registry lists a primary endpoint and several secondary outcomes. These include local recurrence, complete resection, distant recurrence, grade 4 treatment-related toxicity, and 1-year overall survival. The record also indicates 7 outcome measures overall, but results for the listed outcomes are not reported in the registry record.

When a study examines multiple outcomes, the chance of at least one apparently notable finding can increase if each is tested separately without a plan to account for multiplicity. This is a general statistical issue, not evidence that this study did or did not adjust its analyses. A multiplicity strategy is not reported in the registry record. The registry also does not report hypothesis tests or analysis entries, so it is not possible to assess how multiple outcomes were handled.

The primary analysis population is described as all enrolled patients. The record does not explain how participants without an evaluable surgical specimen, missing outcome assessments, withdrawals, or protocol deviations would be handled. Missing-data methods and the number of participants with evaluable primary endpoint data are not reported in the registry record.

The distinction matters because a percentage based on all enrolled participants may be interpreted differently from a percentage based only on those with an evaluable specimen. The registry identifies the intended analysis dataset but does not provide the participant-level disposition needed to assess whether the stated population was fully represented in the endpoint result. No imputation approach, sensitivity analysis, or analysis-population alternative is reported in the registry record.

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 0% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: cytokine release syndrome (15.4%), lymphopenia (15.4%), proctitis (7.7%), rectum, pain (7.7%), rash: acne/acneiform (7.7%).

The registry lists serious adverse events for the group titled Cetuximab With Standard 5-FU and Radiation. It reports 13 participants at risk and 6 affected by serious adverse events. For other adverse events, it reports 13 at risk and 13 affected. The deaths count is 0. These figures are counts of participants affected as recorded, not a tally of every event episode.

The serious-event terms listed include cytokine release syndrome and lymphopenia, each reported at 15.4%, and proctitis, rectum pain, rash described as acne/acneiform, and ulceration, each at 7.7%. The percentages are reproduced as recorded. The list does not establish that the terms occurred in separate participants; a participant can have more than one event. They therefore should not be summed to infer a total affected population.

These safety observations are descriptive for the study group. The registry record does not report a comparator group, event-level timing, duration, or attribution details. The figures cannot determine how much risk is due to cetuximab, 5-FU, radiation, or their combination. They also do not establish the safety profile beyond the participants and observations recorded in this study.

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

The registry record describes a study designed to assess pathological complete response after neoadjuvant cetuximab, 5-FU, and radiation in patients with locally advanced rectal cancer. It defines the response by the absence of tumor cells in the surgical specimen, including lymph nodes, and identifies all enrolled patients as the primary analysis population. Those details clarify what the study set out to measure.

The posted information does not report the primary endpoint result. There is no response count, percentage, or 90% confidence interval in the registry record. Therefore, the available record cannot establish what response rate was observed or how precisely it was estimated. The listed secondary outcomes also lack reported results in the information available for this analysis.

Even a reported response percentage from this study would have to be interpreted as an outcome in a single-group cohort, not as proof that cetuximab improved outcomes compared with 5-FU and radiation alone. There is no concurrent control group listed, and the study is not described as randomized. A comparison to treatment expectations from elsewhere would not be equivalent to a randomized comparison within this study; such external information is not part of the reported results.

The safety counts give a descriptive account of participants affected by serious and other adverse events, and the registry lists several serious-event terms. They do not establish comparative risk or causation. No deaths are listed, but that observation alone does not establish the absence of other clinically important harms.

Accordingly, the registry information supports a careful account of the research question, design, endpoint definition, and recorded safety counts. It does not support a conclusion about efficacy, comparative benefit, the precision of the primary response estimate, or the outcome results for the listed secondary measures.

14. Why This Trial Matters Statistically

This study illustrates why the design and the result must be read together. A pathological complete response rate could describe the outcomes observed after neoadjuvant treatment, but the single-group design does not provide a concurrent treatment contrast. Statistical interpretation depends not only on what endpoint was chosen, but also on how the study could distinguish a treatment effect from other explanations.

The primary endpoint is defined in a clinically interpretable way through surgical pathology, with a stated assessment time tied to surgery. At the same time, the registry record does not report the response count or estimate. The contrast between a clear endpoint definition and missing outcome results is a useful reminder that a prespecified or registered measurement is not itself evidence of an observed result.

The record also shows why uncertainty matters in small studies. Enrollment is 13, and a response estimate in a group of this size would be sensitive to the outcomes of individual participants. A confidence interval is important for communicating that uncertainty; although the registry specifies a 90% confidence interval, it does not report the interval or point estimate.

Finally, safety counts require attention to their unit of analysis. Counts of affected participants, percentages attached to event terms, and counts of individual episodes are not interchangeable. The listed terms may overlap within participants, and the absence of a concurrent comparator prevents an estimate of relative risk. These statistical distinctions help prevent descriptive registry information from being interpreted as a causal or comparative result.

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.

The registry record reports enrollment of 13 and lists a single-group study. Without a concurrent control group, the study cannot directly estimate the difference in pathological complete response between the combination regimen and a regimen without cetuximab. No randomized comparison is reported, and masking is listed as none.

The primary outcome is assessed at surgery, with the registry describing surgery in this cohort as occurring up to 24 weeks from registration. The record does not report the number with an evaluable surgical specimen or how the endpoint would be handled if surgery or pathological assessment were unavailable. Missing outcome handling is not reported in the registry record.

The available intervention description is incomplete. It gives some cetuximab schedule information, but the full treatment regimen and delivery details are not reported in the registry record. The reason the study was terminated is also not reported. These gaps limit interpretation of treatment exposure and study completion.

The record lists no analysis entries and does not report a statistical analysis plan, multiplicity approach, sample-size justification, or endpoint result. Thus, the primary response estimate and its 90% confidence interval cannot be evaluated, and results for secondary outcomes cannot be assessed. The safety information is also descriptive: no comparative risk estimates or detailed event-level circumstances are reported. These limitations are specific to the design and the information recorded for this study.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Cetuximab, 5-FU and Radiation as Neoadjuvant Therapy for Patients With Locally Advanced Rectal Cancer — NCT00611858.
• Registry record last updated 2019-01-08; status last verified 2018-12.
• Results first posted 2018-11-14.
• 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

The registry record describes a Phase II, single-group study of cetuximab with 5-FU and radiation as neoadjuvant therapy for locally advanced rectal cancer. Enrollment is 13, masking is listed as none, and allocation is not applicable. The study is listed as terminated.

The primary endpoint is pathological complete response, defined by the absence of tumor cells in the surgical specimen, including lymph nodes. The stated analysis population is all enrolled patients, and the endpoint has a specified 90% confidence interval. The observed endpoint result and interval are not reported in the registry record.

Safety information lists 6 of 13 participants affected by serious adverse events, 13 of 13 affected by other adverse events, and 0 deaths. The registry record does not provide a concurrent control comparison or results for the listed secondary outcomes.