A Study of Xeloda (Capecitabine) Plus Radiotherapy in Participants With Locally Advanced Rectal Cancer: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for A Study of Xeloda (Capecitabine) Plus Radiotherapy in Participants With Locally Advanced Rectal Cancer (NCT00796718), a na phase 2 study. The primary outcome is Percentage of Participants With Pathological Complete Response.

2. Clinical Question

In practical terms, the study was designed to describe pathological response after combined treatment in this participant group. Surgery posted the occasion for assessing the tumor specimen; the primary outcome was not a symptom score or a time-to-event measure. The registry also lists response assessments after radiochemotherapy and after surgery, as well as adverse events, as secondary outcomes. Those entries provide context for the range of outcomes the study sought to assess, but the record does not report their results in the registry record for this analysis. Without a reported primary response count and its analysis population, the primary question cannot be answered quantitatively from the registry record.

3. Trial Design

This was an open-label, single-group Phase 2 study sponsored by Hoffmann-La Roche. The registry lists the study as completed, with a recorded enrollment of 62. Its study dates are October 2008 for the start and August 2010 for primary completion. Allocation is listed as NA, and masking as none. These features describe a treatment study without a randomized concurrent comparator; they do not support a direct treatment contrast between assigned groups.

The treatment combined capecitabine, also called Xeloda, and standard radiotherapy. The planned regimen in the brief summary was capecitabine 825mg/m^2 orally twice daily with standard radiotherapy for 5 weeks, followed by surgery within 6 weeks after treatment. The brief summary anticipated time on study treatment of < 3 months and described a target sample size of < 100 individuals. These are registry descriptions, not evidence that every participant received the same duration or completed each treatment step.

The primary outcome was the percentage of participants with pathological complete response, assessed at post-treatment surgery up to 11 weeks. The registry defines this response as absence of viable tumor cells in the tumor specimen, including regional lymph nodes, as determined by standard histological procedures. The primary outcome population is described as participants with available data.

Secondary outcomes included response assessments 4-6 weeks after radiochemotherapy, response assessed 1 month after surgery, and adverse events. The registry lists 4 outcome measures but no analyses. A detailed statistical plan, including any adjustment strategy or missing-data procedure, is not reported in the registry record. The design information establishes the treatment setting and measurement schedule, but not the amount of observed benefit or the precision of the primary estimate.

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 62 participants were enrolled in the study.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Participants with available data.

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: All enrolled participants.

6. Primary Endpoint

The registry lists the primary outcome as Percentage of Participants With Pathological Complete Response, measured over Up to 11 weeks (assessed at the time of post-treatment surgery).

The primary endpoint was the percentage of participants with pathological complete response at post-treatment surgery, assessed up to 11 weeks. A pathological complete response was defined as no viable tumor cells in the tumor specimen, including regional lymph nodes, using standard histological procedures. The endpoint is therefore based on examination of tissue after treatment rather than on a clinical impression alone.

In general, a pathological response endpoint can describe whether viable tumor is detected in the examined surgical specimen after treatment. It gives a defined outcome at a specified assessment occasion and can be summarized as a proportion of the relevant participants. This makes it distinct from outcomes that measure time until an event, symptom changes, or adverse events. The endpoint’s meaning depends on having a clear response definition and on knowing which participants were assessed.

The registry record identifies participants with available data as the primary population but does not report how many had endpoint data, how many met the response definition, or the resulting percentage. It also does not give a confidence interval or a statistical test for this outcome. Consequently, the endpoint definition is available, but its observed frequency and precision cannot be described from the registry record. The endpoint itself is a pathological measure; it should not be treated as a direct measure of every aspect of clinical outcome or as a comparison with another treatment.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does a single-group study estimate?

In general, a single-group study can estimate the frequency of an outcome among participants who received the study regimen and had outcome information. For a binary outcome such as pathological complete response, the basic summary is a proportion: the number meeting the response definition relative to the number assessed. This describes the observed group. It does not, on its own, estimate what would have happened to the same participants under a different treatment.

This study is recorded as single-group, with allocation listed as NA and masking as none. There is no randomized comparator. Consequently, a contrast between treatment groups cannot be calculated from this design. Even if the response count were reported, interpretation would be descriptive unless a suitable comparison and a corresponding analysis were available. Other influences on outcomes cannot be disentangled from treatment in a single-group summary.

How should a percentage endpoint be read?

In general, a percentage for a binary endpoint expresses the fraction of the analysis population that experienced the defined event. Its interpretation depends on a clear definition of the event and a clear denominator. Here, the registry defines pathological complete response as absence of viable tumor cells in the tumor specimen, including regional lymph nodes, and identifies the population as participants with available data. It does not report the count meeting the definition or the number with available data, so the response percentage cannot be reconstructed or interpreted from the record.

A confidence interval, in general, describes uncertainty around an estimated quantity under a statistical model. For a proportion, it can show how much precision the observed data provide. A narrow interval generally indicates greater precision than a wide interval, but precision is not the same as clinical importance, and an interval does not remove limitations of a single-group design. No confidence interval for the primary endpoint is reported in the registry record.

What can an inferential test establish?

In general, a statistical test evaluates data against a specified null hypothesis under assumptions set by the analysis. Its result depends on the endpoint, analysis population, model, and testing plan. A p-value does not measure the probability that a treatment works, and it does not quantify the size of an effect. An effect estimate and its uncertainty are needed to describe magnitude and precision.

The record lists no analyses. It does not report a p-value, model, test, confidence interval, or adjusted estimate for the primary response endpoint. The statistical plan, including whether any planned hypothesis test existed, is not reported in the registry record. No inferential conclusion should therefore be attributed to the study based on the information recorded.

Why does the analysis population matter?

In general, the analysis population specifies which participants contribute to a particular estimate. A group may be defined by enrollment, treatment received, or availability of outcome information, among other possibilities. These populations answer different questions and can yield different estimates when some participants lack measurements or do not follow the intended treatment course. Clear reporting of the population and the number assessed allows readers to understand the denominator and evaluate the scope of the result.

For the primary endpoint, the registry says participants with available data, but does not state the number assessed or explain how missing observations were handled. It does not report whether the primary analysis used another population definition. Thus, the enrolled number should not be substituted for the unknown endpoint denominator.

What does over-dispersion mean in general?

Over-dispersion is a general statistical issue in which observed variability is greater than a model expects. It can arise in some count or binary-data settings when outcomes vary more across participants or clusters than assumed by a simple model. If a model ignores over-dispersion, standard errors and uncertainty intervals may be too small, making estimates appear more precise than warranted. Whether this issue was relevant or assessed in this study is not reported in the registry record. No model details are available to evaluate it for the primary endpoint.

How should sample-size planning be understood?

In general, a sample-size calculation uses assumptions about the outcome, effect to detect, allocation, significance level, and desired power to illustrate what a future study might require. It is a planning exercise, not a result observed in the participants enrolled. The registry describes a planning illustration using a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation, with the effect expressed as a fraction of the observed effect. It specifies that time-to-event planning uses a total event count and other planning outputs use participants per arm.

The registry record does not give the observed primary effect or numerical planning outputs in the registry record for this analysis. Since the actual study is single-group, the stated equal-allocation, two-arm assumptions do not describe its treatment allocation. The planning illustration should not be mistaken for the trial’s own design, observed power, or evidence from a randomized comparison. The trial’s sample-size justification is not reported in the registry record.

What can safety summaries tell readers?

In general, adverse-event counts and percentages describe events recorded during a study, subject to the definitions, observation period, and reporting practices used. Serious and non-serious categories are not interchangeable. A count of participants with an event is also distinct from a count of all event episodes, since one participant may experience more than one event. The registry lists serious and other adverse-event counts but does not explain event-level counting details, attribution, or the full observation window. The listed figures should therefore be read as registry summaries rather than as a complete causal assessment.

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("Capecitabine")
n      <- c(50)
events <- c(8)
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  Capecitabine  50  8  16.0  7.2  29.1  8.3  28.5  8.4  28.6

11. Multiplicity, Missing Data and Analysis Populations

The registry lists 4 outcome measures: the primary pathological complete response measure and secondary response assessments after radiochemotherapy, after surgery, and adverse events. Multiple outcomes can create multiplicity: when many hypotheses are tested, the chance of at least one apparently unusual result can rise if no adjustment or prespecified testing hierarchy is used. In general, a study may address this through a testing plan, adjustment, or clear distinction between primary and exploratory outcomes.

The registry record does not report a multiplicity strategy, a hierarchy for secondary outcomes, or whether formal hypothesis tests were planned. It lists no analyses. It is therefore not possible to determine whether any adjustment was used or to interpret a family of inferential results. The primary endpoint is identified, but that designation alone does not reveal how testing across outcomes was handled.

Missing data also affect the interpretation of a percentage. The primary population is described as participants with available data, but the record does not state the number assessed, the amount of missing endpoint information, reasons for missingness, or any method for handling missing observations. In general, a complete-case proportion describes participants with observed outcomes and may not represent everyone enrolled if missingness is related to participant characteristics or outcomes. That possibility cannot be evaluated from this record.

The analysis populations for the secondary outcomes are not reported in the registry record. Nor does the record explain how participants who did not undergo surgery, if any, would be handled for the pathological endpoint. These details should not be inferred. Without a reported analysis population and missing-data approach, the denominator, representativeness, and robustness of the primary estimate cannot be assessed.

12. Safety Results

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

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: diarrhea (3.2%), ventricular fibrillation (1.6%), hemorrhoidal inflammation (1.6%), ileus (1.6%), sepsis (1.6%).

The registry lists 4 participants in the serious adverse-event count among 62 at risk. It separately lists 49 participants in the other adverse-event count among 62 at risk. These are registry categories; the record does not explain whether individuals could appear in both categories, how multiple events per participant were counted, or the full period over which events were collected. The figures should not be added or treated as mutually exclusive groups.

The serious adverse-event terms listed include diarrhea at 3.2%, ventricular fibrillation at 1.6%, hemorrhoidal inflammation at 1.6%, ileus at 1.6%, and sepsis at 1.6%. These percentages are quoted as recorded; the registry excerpt does not provide additional event counts for each term or describe attribution to treatment. The safety entry does not report a death count.

In general, adverse events occurring during a study do not by themselves establish that the study treatment caused them. Interpretation depends on definitions, timing, clinical assessment, and a suitable comparison. Since this was a single-group study, the listed safety counts do not provide a like-for-like estimate of comparative risk. They are descriptive safety information, not a causal conclusion.

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

The record establishes that a Phase 2, open-label, single-group study evaluated capecitabine plus standard radiotherapy in participants with locally advanced rectal cancer. It specifies the treatment sequence, the primary pathological response definition, and selected safety summaries. Those details clarify what the study set out to assess and how the primary outcome was defined.

It does not establish the observed frequency of pathological complete response. The primary response count, endpoint denominator, percentage estimate, and uncertainty interval are not reported in the registry record. The study’s enrollment of 62 does not substitute for the unknown number with primary outcome data. Without an observed estimate, the magnitude and precision of the primary result cannot be described.

Even a reported response proportion from this design would be a description of the treated group, not a randomized estimate of comparative treatment effect. A single-group study lacks a concurrent control group to distinguish outcomes under the regimen from outcomes under another treatment or other influences. The record lists no analyses, so it also does not support a reported inferential conclusion.

The safety entries show that serious and other adverse-event counts were recorded, with several serious-event terms and percentages listed. These data can be read as descriptive registry reporting, but they do not establish causation or comparative safety. Details about event attribution and the observation period are not reported.

Accordingly, the available record supports a description of study design, endpoint definitions, and selected safety information. It does not support a numerical conclusion about the primary response, its precision, or a causal treatment effect. The study’s completed status should not be interpreted as a reported result, and the planning framework should not be interpreted as observed power.

14. Why This Trial Matters Statistically

This trial is statistically informative as an example of the difference between a defined endpoint and a reported result. The registry clearly defines pathological complete response and identifies the assessment occasion, yet does not report the outcome count or percentage. A precise endpoint definition is essential, but it cannot replace the observed data needed to estimate an outcome.

The single-group design also makes the scope of inference important. A study can describe outcomes among participants receiving a regimen, but without a concurrent comparison group it cannot establish how those outcomes differ from an alternative. Readers should distinguish descriptive response from comparative effect, and should not treat treatment sequence or study completion as evidence of effectiveness.

The record further illustrates why denominator and missing-data reporting matter. The primary population is described as participants with available data, but the number assessed is not stated. Without that information, readers cannot determine how the response proportion would be defined or assess whether missing observations could affect its interpretation.

Finally, the safety entries reinforce the distinction between event reporting and causal attribution. Counts and listed percentages can identify what the registry records, but a single-group record cannot supply a like-for-like comparison of safety. The study therefore matters statistically less as a source of a quantifiable treatment effect in this record, and more as a reminder that design, endpoint definition, analysis population, and complete result reporting jointly determine what conclusions can be drawn.

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 primary limitation for interpreting this study from the registry record is that its primary result is not reported. The endpoint count, the number assessed, the resulting percentage, and any uncertainty interval are absent. The primary analysis population is described only as participants with available data, so the denominator and potential impact of missing outcomes cannot be evaluated.

The single-group design has no randomized comparator. It can describe outcomes in the treatment group if results are reported, but cannot provide a randomized comparison or isolate treatment effects from other explanations. The open-label design is also recorded; the registry does not describe any masking of outcome assessment.

The registry lists no analyses and does not report the statistical plan, sample-size justification, multiplicity approach, or missing-data procedure. It is therefore not possible to assess model choice, prespecification, adjustment, or sensitivity analyses. The planning illustration’s stated assumptions do not constitute the trial’s own design or an observed power calculation.

Safety reporting is also limited in the available record. The listed counts and terms do not include details about attribution, timing, event-level counting, or whether participants could contribute to more than one category. The death field is not reported in the registry record. These limitations restrict interpretation to the descriptive information explicitly recorded.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: A Study of Xeloda (Capecitabine) Plus Radiotherapy in Participants With Locally Advanced Rectal Cancer — NCT00796718.
• Registry record last updated 2016-08-25; status last verified 2016-07.
• Results first posted 2016-08-25.
• 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

NCT00796718 is a completed, open-label, single-group Phase 2 study sponsored by Hoffmann-La Roche. The registry records enrollment of 62, with a start in October 2008 and primary completion in August 2010. Participants received capecitabine plus standard radiotherapy, followed by surgery according to the described treatment schedule.

The primary outcome was the percentage with pathological complete response at surgery, defined by absence of viable tumor cells in the tumor specimen, including regional lymph nodes. The registry record does not report the primary response result, its denominator, or an inferential analysis. It lists 4 outcome measures and no analyses.

Safety entries include 4 participants in the serious adverse-event count and 49 in the other adverse-event count, each among 62 at risk, along with serious-event terms and percentages. These entries are descriptive and do not establish causation. A comparative treatment effect and the precision of the primary response estimate cannot be determined from the registry record.