NKTR-102 in Combination With Cetuximab in Patients With Refractory Solid Tumors (Phase 2a) and Metastatic or Locally Advanced Colorectal Cancer (Phase 2b): Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for NKTR-102 in Combination With Cetuximab in Patients With Refractory Solid Tumors (Phase 2a) and Metastatic or Locally Advanced Colorectal Cancer (Phase 2b) (NCT00598975), a non-randomized phase 2 study. The primary outcome is Number of Patients With Dose Limiting Toxicities.

2. Clinical Question

The study record describes a multicenter, open-label phase 2 study with sequential phase 2a and phase 2b components. In phase 2a, the stated purpose was dose finding among patients with solid tumors refractory to standard treatment. The stated phase 2b aim was to evaluate treatment in second-line metastatic colorectal cancer. The brief description names progression-free survival as the phase 2b primary endpoint, but the registry’s posted primary outcome is the count of patients with dose-limiting toxicities. These descriptions refer to different components and do not establish that phase 2b outcomes are included in the posted results.

Statistically, the central question that can be addressed from the posted outcome information is limited: how many patients experienced dose-limiting toxicity during the stated timeframe? The record gives the endpoint definition and analysis population, but not its observed count or an estimate of uncertainty. The listed dose groups can be described, but the record identifies the overall allocation as nonrandomized, so they should not be treated as equivalent randomized groups for a causal comparison.

3. Trial Design

NCT00598975 is recorded as a completed phase 2 study sponsored by Nektar Therapeutics. The registry lists a start date of 2008-02, a primary completion date of 2009-05, and enrollment of 18. The official title describes a multicenter, open-label study assessing NKTR-102, or PEG-irinotecan, with cetuximab in refractory solid tumors and colorectal cancer. The brief description separates the study into sequential phase 2a and phase 2b components.

The phase 2a description characterizes that component as open-label dose finding in multiple solid tumor types refractory to standard curative or palliative therapies. Its stated primary purpose was to establish a recommended phase 2 dose by measuring dose-limiting toxicity. The listed arm descriptions show NKTR-102 100 mg/m2 plus cetuximab and NKTR-102 125 mg/m2 plus cetuximab. The arm descriptions also refer to additional sequential dose cohorts, but the posted arms are limited to those two dose groups.

The brief summary describes phase 2b as a randomized, two-arm comparison of NKTR-102 plus cetuximab against irinotecan plus cetuximab in second-line metastatic colorectal cancer. In contrast, the registry’s allocation field identifies the study as nonrandomized, and the posted arm descriptions list two NKTR-102 dose groups rather than an irinotecan comparator. The record does not resolve this difference or establish which component contributed the posted participants and safety results. As a result, the phase 2b description should not be used to interpret the dose-group counts as a randomized treatment comparison.

Masking is listed as none, consistent with the open-label description. The model is listed as parallel. These design labels do not establish that the two posted dose groups were comparable at baseline. Phase-specific enrollment, the allocation sequence, eligibility details for the posted participants, and any rationale for the planned enrollment are not reported in the registry record.

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: ITT/Safety Population

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 Number of Patients With Dose Limiting Toxicities, measured over 12 months.

The primary endpoint is the number of patients with dose-limiting toxicities. It is recorded as a participant count over 12 months in the ITT/Safety Population. A count endpoint records how many people meet an event definition; it is not itself a risk estimate or a comparison between treatments. The registry description does not provide the numerical count or a more detailed operational definition of dose-limiting toxicity for this primary outcome.

In a dose-finding study, dose-limiting toxicity is used to assess whether treatment-related toxicity constrains dose selection. The general rationale is that dose-finding decisions need to consider tolerability alongside the planned treatment exposure. The study summary states that the phase 2a component aimed to establish a recommended phase 2 dose by measuring the frequency of dose-limiting toxicity. However, the posted primary endpoint is worded as a number of patients, and the record does not give the result needed to assess that frequency.

The registry also lists “Number of Patients With Dose Limiting Toxicities by NCI-CTCAE” and “Number of Patients With Overall Response” among secondary outcomes. The primary outcome and secondary toxicity outcome are related in topic, but their specific definitions and relationship are not explained in the record. Nor is a numerical primary-endpoint result posted. Consequently, the endpoint’s intended role can be described, but its observed result cannot be interpreted from the available registry results.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does a participant count tell us?

A participant count is a direct summary of how many people met an outcome definition. It is useful for describing events in a study group, but a count alone does not express the probability of an event unless it is considered with the number of participants assessed and the follow-up rules. Even with a denominator, a proportion is still an estimate subject to uncertainty, particularly when group sizes are limited. General statistical practice therefore distinguishes an observed count from an estimate of the underlying event frequency.

For this study, the primary outcome is a count of participants with dose-limiting toxicities, and the stated timeframe is 12 months. The record does not give the count or the details needed to determine how participants with incomplete follow-up were handled. The posted serious adverse event counts are separate safety summaries; they should not be substituted for the missing primary endpoint result.

Why does allocation matter?

Random assignment is a design method intended to make treatment groups comparable, on average, with respect to measured and unmeasured characteristics. Without random assignment, differences in outcomes across groups can reflect who received each dose, differences in care or follow-up, or other factors, as well as any effect associated with the treatment. General statistical adjustment may address recorded differences, but it cannot guarantee removal of bias from unmeasured factors.

The registry lists allocation as nonrandomized. Therefore, the two posted dose groups should be interpreted descriptively rather than as a randomized head-to-head comparison. The brief summary describes a randomized phase 2b component, but the posted arm descriptions and allocation field do not match that description. The registry record does not explain the discrepancy or identify analyses that reconcile it.

How should uncertainty be considered?

A confidence interval is a statistical range that represents uncertainty around an estimate under a specified method and assumptions. A narrow interval generally indicates greater precision, while a wide interval indicates that a range of underlying values remains compatible with the data. General interpretation requires considering the endpoint, sample size, analysis method, and assumptions together; an interval is not a guarantee that the true value lies within its limits.

No confidence interval or other inferential estimate for the primary endpoint is reported in the registry record. No p-value or treatment-effect estimate is posted for the listed outcomes. Without such results, the primary outcome cannot be assessed for precision, and there is no basis for describing statistical evidence of a difference between the dose groups.

What do the sample-size assumptions mean?

The registry’s sample-size assumptions describe a planning illustration based on an observed effect, with a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. The assumed effect is described as a stated fraction of the observed effect. The record distinguishes total events for time-to-event illustrations from participants per arm for other illustrations. These are planning assumptions, not a report of the study’s original design rationale.

Such illustrations can show how a hypothetical study’s size relates to a selected effect and statistical assumptions. They do not establish the actual power of the completed study. Sample-size calculations are not observed power: after a study, the relevant interpretation comes from the effect estimate and its uncertainty, not a retrospective power value. In this case, no numerical primary endpoint estimate or inferential analysis is posted, so the illustration cannot supply the missing outcome evidence.

Over-dispersion is a general issue when outcome variability is greater than a statistical model expects. If ignored, standard errors may be too small and intervals or tests may appear more precise than warranted. The registry record does not describe a model for the primary count outcome, whether over-dispersion was evaluated, or whether any adjustment was used. It would be inappropriate to attribute a particular count model or variance assumption to the study.

What can be concluded from the available analyses?

The registry lists no analyses. It also does not identify an analysis population beyond the primary endpoint’s ITT/Safety Population label, nor explain the meaning of that combined label. A named population does not by itself specify how participants were included, how treatment changes were handled, or how missing outcome data were addressed. The posted information therefore supports a limited descriptive reading of the enrollment and safety counts, but not a reconstruction of the statistical analysis plan.

10. Multiplicity, Missing Data and Analysis Populations

Multiplicity arises when a study examines multiple outcomes, time points, treatment groups, or analyses. If many statistical tests are conducted, the chance of at least one apparently unusual result can rise unless the analysis plan addresses that issue. General approaches include prespecifying a primary outcome, defining a testing order, or adjusting inference. The registry lists a primary endpoint and secondary outcomes, but details of any multiplicity strategy are not reported in the registry record. The record also lists no analyses, so it is not possible to determine which tests, if any, were conducted or how their interpretation was managed.

The study summary names response rate, response duration, overall survival, pharmacokinetics, and toxicities as secondary endpoints across the phase 2a and phase 2b components. The posted secondary outcomes include dose-limiting toxicity by NCI-CTCAE and overall response. The registry does not provide numerical results for these outcomes in the information available, and the relationship between the listed endpoint names and the phase-specific objectives is not fully described.

Missing-data methods are not reported in the registry record. The record does not state how participants who discontinued, missed assessments, or lacked endpoint information were handled, or whether follow-up differed across groups. This matters because a count of observed events may not represent all participants equally if outcome ascertainment is incomplete.

The primary outcome names the ITT/Safety Population, but the registry does not define that population or explain how the two labels were combined. The sample-size assumptions describe equal allocation as part of a planning illustration, while the posted group sizes are 12 and 6 and the trial allocation is listed as nonrandomized. The record does not state how these registry entries relate to the original design or to the analyses. Interim analyses, stopping rules, and a detailed statistical analysis plan are not reported in 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: diarrhea (16.7%), gastrointestinal haemorrhage (16.7%), intestinal obstruction (16.7%), renal acute failure (16.7%), deep vein thrombosis (16.7%).

The registry’s serious adverse event summary lists 12 participants at risk in the NKTR-102 100 mg/m2 plus cetuximab group, of whom 5 were affected, and 6 at risk in the NKTR-102 125 mg/m2 plus cetuximab group, of whom 3 were affected. The total lists 18 at risk and 8 affected. These figures describe the recorded serious adverse event burden in the groups; they do not show that the events were caused by treatment.

The death counts are 1 in the 100 mg/m2 group, 0 in the 125 mg/m2 group, and 1 overall. The record does not provide further detail about the death or its relationship to study treatment. The listed serious-event terms include diarrhea, gastrointestinal haemorrhage, intestinal obstruction, renal acute failure, deep vein thrombosis, and small intestinal obstruction. The registry gives percentages for these terms, including 16.7% for several terms and 8.3% for small intestinal obstruction.

These term-level percentages should not be added or treated as mutually exclusive categories: the record does not explain whether one participant could appear under more than one term or give a denominator for each term. Nor does it report event timing, duration, severity beyond serious-event classification, or a comparison adjusted for group characteristics. With nonrandomized groups and differing group sizes, the counts are descriptive and are not a like-for-like estimate of comparative safety.

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

The registry record documents a phase 2 study of NKTR-102 with cetuximab, with posted groups receiving NKTR-102 at 100 mg/m2 or 125 mg/m2. It identifies dose-limiting toxicity as the primary outcome and provides its timeframe and named analysis population. The available numerical results include enrollment and selected serious adverse event counts. This supports a description of what was recorded, but not an estimate of efficacy or a full assessment of toxicity.

The record does not report the primary endpoint’s observed count. It also does not report numerical results for the listed response outcomes or the phase 2b progression-free survival objective. Therefore, it does not establish the frequency of dose-limiting toxicity, the size or direction of an efficacy effect, or the precision of any such effect. The absence of a posted result is not evidence that an outcome did not occur.

The serious adverse event counts and death counts provide descriptive safety information. They do not demonstrate causality, and they do not establish that one NKTR-102 dose is safer than the other. The nonrandomized allocation and the difference in group sizes limit direct comparison. In addition, the record does not include details about baseline characteristics, follow-up completeness, event adjudication, or statistical adjustment that could clarify those comparisons.

The brief summary’s description of a randomized phase 2b comparison with irinotecan plus cetuximab differs from the registry allocation label and the posted arm descriptions. The record does not resolve whether the posted results represent only the dose-finding component or also include participants from the described phase 2b component. Conclusions about a randomized comparison would therefore go beyond what the posted information establishes.

In short, the record supports a narrow account of the trial design and reported safety counts. It does not support a treatment recommendation or a definitive judgment about treatment effects. Interpreting efficacy or comparative safety would require outcome results and methodological details that are not reported in the registry record.

13. Why This Trial Matters Statistically

This study illustrates why design labels and endpoint results need to be read together. The brief description presents distinct phase 2a and phase 2b aims, including dose finding and a proposed randomized comparison. Yet the registry identifies allocation as nonrandomized and lists two NKTR-102 dose groups. When descriptions do not align, it is important not to infer a randomized treatment contrast from the study summary alone.

It also illustrates the difference between an endpoint definition and an endpoint result. Naming a dose-limiting-toxicity count, its timeframe, and an analysis population clarifies what was intended to be measured, but does not reveal how many participants experienced the outcome. Statistical interpretation depends on the result and its uncertainty, not only on the label of the endpoint.

The safety data show another central issue: descriptive counts are not equivalent to causal comparisons. Serious adverse event counts can be useful for documenting what occurred, while nonrandomized allocation, unequal group sizes, and missing contextual details constrain comparisons. A reader should distinguish the registry’s event descriptions from conclusions about treatment attribution or dose differences.

Finally, the record demonstrates the importance of transparent reporting. Numerical outcomes, analysis methods, missing-data handling, and the relationship between study components are necessary to evaluate precision and bias. Where those details are absent, a careful statistical account should state the limits rather than fill them with assumptions. This distinction is especially important in small phase 2 records, where a few observations can strongly influence descriptive summaries and where formal inference may be limited or unavailable.

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 most direct limitation is that the numerical result for the primary dose-limiting-toxicity endpoint is not reported in the registry record. The record also lacks numerical results for the response outcomes and the progression-free survival objective described for phase 2b. As a result, the stated clinical questions cannot be evaluated using endpoint estimates or measures of uncertainty.

The phase-specific design is unclear in the posted information. The brief summary describes sequential components and a randomized phase 2b comparison, while the allocation field is nonrandomized and the posted arms are two NKTR-102 dose groups with cetuximab. Phase-specific enrollment, the actual allocation process, and an explanation of this difference are not reported in the registry record. The posted group counts therefore cannot be assumed to represent a randomized comparison.

Further limitations include the absence of baseline characteristics, detailed eligibility information for the posted groups, endpoint definitions beyond brief labels, and a statistical analysis plan. Handling of missing data, follow-up, protocol deviations, and multiplicity is not reported in the registry record. The primary outcome names the ITT/Safety Population, but the population’s definition is not given. The record also does not explain the denominator or overlap rules for the term-specific serious adverse event percentages.

The safety summaries are descriptive and do not include enough information to evaluate event timing, attribution, or adjusted differences between groups. The sample-size assumptions are described as planning illustrations based on an observed effect, not as the study’s own design justification. These limitations preclude a fuller assessment of precision, bias, and the relationship between the posted safety figures and the study’s intended phase-specific objectives.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: NKTR-102 in Combination With Cetuximab in Patients With Refractory Solid Tumors (Phase 2a) and Metastatic or Locally Advanced Colorectal Cancer (Phase 2b) — NCT00598975.
• Registry record last updated 2021-07-12; status last verified 2021-07.
• Results first posted 2021-06-14.
• 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.

18. Record Summary

NCT00598975 is a completed phase 2 study sponsored by Nektar Therapeutics, with enrollment of 18. The record describes NKTR-102, or PEG-irinotecan, with cetuximab and lists arms receiving NKTR-102 100 mg/m2 or 125 mg/m2 with cetuximab. The primary endpoint is the number of patients with dose-limiting toxicities over 12 months in the ITT/Safety Population.

The posted safety data include serious adverse event counts of 5 of 12 in the 100 mg/m2 group and 3 of 6 in the 125 mg/m2 group, with 8 of 18 overall. Death counts are 1, 0, and 1 overall, respectively. The numerical primary endpoint result and efficacy results are not reported in the registry record. The allocation label is nonrandomized, while the brief summary describes a randomized phase 2b component; the record does not explain this difference.