Study of NKTR 255 in Combination With Cetuximab in Solid Tumors: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Study of NKTR 255 in Combination With Cetuximab in Solid Tumors (NCT04616196), a na phase 1, phase 2 study. The primary outcome is Incidence of Treatment-Emergent Adverse Events (TEAE) and Serious Adverse Events (SAE) of NKTR-255 in Combination With Cetuximab in R/R HNSCC or CRC for Phase 1b Dose Escalation.

2. Clinical Question

3. Trial Design

This is a Phase 1b/2, open-label, multicenter study of NKTR-255 as monotherapy or in combination with cetuximab for solid tumors. The listed conditions are head and neck squamous cell carcinoma and colorectal cancer. The official title describes the treatments as a salvage regimen. The record describes a sequential design, with allocation listed as not applicable and masking as none.

The primary safety outcome is specifically titled for Phase 1b dose escalation of NKTR-255 with cetuximab in recurrent or refractory HNSCC or CRC. The listed dose-escalation groups correspond to NKTR-255 levels of 1.5 µg/kg, 3.0 µg/kg, 4.5 µg/kg, and 6.0 µg/kg, each with cetuximab. The arm description says the dose escalation was intended to establish the RP2D. The registry record does not report additional details of the escalation rules or the definition of RP2D.

The study enrolled 25 participants and is marked completed. Its recorded start date is 2020-10-30, and its primary completion date is 2023-03-30. Those dates describe the registry record; they do not establish when every participant began or completed treatment. The record includes 2 outcome measures, while no analyses are listed. Available safety counts are reported for the four combination dose groups. Because this was not a randomized comparison, the groups are not interchangeable control and treatment arms. Any differences in their recorded event counts are descriptive and may reflect differences in the participants or the sequence of dose escalation, not a controlled estimate of a dose effect.

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: The Phase 1 portion of the study was completed. The Phase 2 cohort enrollment was not initiated.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: DLTs were assessed using the DLT Population, which only included patients who received at least 1 dose of the combination treatment of NKTR-255 and cetuximab and who completed the DLT observation period or discontinued from the study treatment due to a DLT, where DLT window was 21 days since the first dose of NKTR-255. The other rows were assessed using the Safety Population, patients who received at least 1 dose (or partial dose) of NKTR-255.

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: Only 23 participants were dosed with NKTR-255 (7 in Level 1, 7 in Level 2, 6 in Level 3, 3 in Level 4) and are included in the Safety Population analysis used for the remainder of results data.

6. Primary Endpoint

The registry lists the primary outcome as Incidence of Treatment-Emergent Adverse Events (TEAE) and Serious Adverse Events (SAE) of NKTR-255 in Combination With Cetuximab in R/R HNSCC or CRC for Phase 1b Dose Escalation, measured over 60 days after the last dose of study treatment, up to an average of 6 months..

The primary endpoint is the incidence of treatment-emergent adverse events and serious adverse events for NKTR-255 combined with cetuximab in recurrent or refractory HNSCC or CRC during Phase 1b dose escalation. It is expressed as a count of participants. The description frames safety and tolerability through several kinds of events: dose-limiting toxicities, drug-related adverse events, serious adverse events, events leading to discontinuation, deaths, and clinical laboratory abnormalities assessed per CTCAE 5.0.

Safety endpoints are used in early-phase studies to characterize observed harms and support decisions about dose and further study. In general, counting participants with events gives a direct description of how many people in a group experienced an event, but it does not by itself convey event severity, duration, recurrence, or attribution. The registry record also specifies a timeframe of 60 days after the last dose of study treatment, up to an average of 6 months. It defines a DLT population including participants who received at least 1 dose and completed the DLT observation period or discontinued because of a DLT. The stated DLT window is 21 days, but the description is truncated before its timing anchor is complete.

The posted group counts do not provide a full account of every component named in the endpoint description. Detailed results for drug relationship, discontinuations, laboratory abnormalities, and DLTs are not reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry record identifies a safety endpoint based on counts of participants, rather than a continuous measurement or time-to-event estimate. That choice determines what the counts can communicate: they tell how many participants in each listed group were recorded as having an event. They do not, by themselves, describe how many events each participant experienced, how long events lasted, or when they occurred.

What does a count describe?

In general, a participant count is a straightforward summary of an event occurrence within a defined group and follow-up period. Its interpretation depends on the event definition, the population included, and the completeness of follow-up. A count without a clearly reported denominator is difficult to interpret as a rate. The safety groups list both participants at risk and participants affected, which allows the posted counts to be read within each dose group. These are still small groups, and the counts remain descriptive rather than comparative estimates.

The registry distinguishes serious adverse events from other adverse events in its group summaries. These categories should not be collapsed into a single measure: seriousness is a specific classification, while the record does not give the detailed criteria or event-level information needed to characterize each occurrence. The listed “other” adverse-event counts do not identify specific events. The primary endpoint description names additional safety components, including drug-related events, discontinuations, deaths, and laboratory abnormalities, but the available record does not provide detailed results for each component.

Why does study design matter?

In general, random assignment helps make treatment groups comparable at the start of a study, supporting causal comparisons when other design and analysis conditions are met. This study is described as sequential, open-label, and without applicable allocation; the registry explicitly cautions that its arms are not a like-for-like control comparison. Participants in different dose groups therefore cannot be assumed to be exchangeable. Changes in counts across groups can reflect the small group sizes or other differences as well as any effect of dose. The observed pattern alone cannot isolate a dose-related cause.

Open-label means masking was absent in the registry record. In general, knowledge of treatment can affect reporting, assessment, or management of events, although the record does not quantify whether such effects occurred. For objective counts, the event definitions and ascertainment procedures still matter. The endpoint refers to CTCAE 5.0 for clinical laboratory abnormalities, but further details of event assessment are not reported in the registry record.

What can uncertainty estimates add?

In general, a confidence interval gives a range of values compatible with the observed data under a statistical model and conveys precision, not certainty that a particular value is true. Small groups typically make estimates less precise. No confidence intervals are included in the available the registry entries, so the precision of the group-level event frequencies cannot be assessed from interval estimates. No p-values or adjusted analyses are listed either. The record reports no analyses, and no statistical model or hypothesis test is described.

In general, over-dispersion arises when variability in observed counts exceeds what a chosen model expects; ignoring it can make uncertainty appear too small. That issue would matter if a count model were used, but no such model or count-analysis result is reported. The posted safety results are counts, not evidence that a particular statistical distribution or inferential model was used.

How should planning calculations be read?

Any sample-size planning illustration based on an observed effect is a hypothetical design calculation, not an observed treatment result or a measure of the study's power after completion. The stated planning assumptions use 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. The record does not state that these assumptions were the trial's own design basis. They do not turn the sequential dose groups into a randomized comparison. No sample-size justification or power analysis for the trial itself is reported in the registry record.

For binary outcomes, general planning calculations depend on the assumed event frequencies and the effect to be detected. A planning result is conditional on those assumptions and should not be treated as a forecast of what the study would observe. In particular, an illustration derived from observed data is not “observed power,” and it cannot resolve the limitations of small, nonrandomized safety groups. The registry record does not report the protocol's sample-size justification, interim analyses, or a statistical analysis plan.

10. Multiplicity, Missing Data and Analysis Populations

The registry record lists 2 outcome measures but no analyses. It does not report a statistical analysis plan, a hierarchy of endpoints, or procedures for handling multiple comparisons. Multiplicity becomes relevant when several outcomes, dose groups, time points, or statistical tests are examined: without a prespecified strategy, the chance of an apparently notable finding among many analyses can be difficult to interpret. No inferential comparisons are available to assess under such a strategy.

Missing-data handling is not reported in the registry record. In general, safety summaries depend on who was observed, how long participants were followed, and how events after treatment discontinuation were captured. The primary endpoint specifies a follow-up timeframe of 60 days after the last dose, up to an average of 6 months, while the DLT population has a separate observation-period definition. The record does not explain how incomplete follow-up, missing assessments, or participants excluded from a particular safety population were handled.

The DLT population is described as including participants who received at least 1 dose of the combination and completed the DLT observation period or discontinued because of a DLT. This differs from simply describing everyone enrolled, but the available record does not provide the size of that population or detailed participant flow. The DLT window is stated as 21 days, with the timing anchor cut off in the description. Further analysis-population definitions are not reported in the registry record.

Without these details, it is not possible to determine whether all endpoint components used the same participants and follow-up, or how missing information could affect the counts. No assumptions about imputation, censoring, or sensitivity analyses should be inferred.

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: cytokine release syndrome (33.3%), cellulitis (16.7%), lung infection (16.7%), sepsis (16.7%), urinary tract infection (16.7%).

The listed serious adverse event counts are 2 of 7 participants at NKTR-255 Level 1 (1.5 µg/kg), 2 of 7 at Level 2 (3.0 µg/kg), 5 of 6 at Level 3 (4.5 µg/kg), and 1 of 3 at Level 4 (6.0 µg/kg), each with cetuximab. The corresponding counts for other adverse events are 7 of 7, 7 of 7, 6 of 6, and 2 of 3. These are participant counts within the dose groups, not counts of all individual event episodes.

The death counts listed for those same groups are 2, 4, 1, and 1. The registry record does not state whether these deaths were considered related to study treatment, nor does it provide causes or timing. They should not be read as treatment-attributed deaths. The record also lists cytokine release syndrome at 33.3%, and cellulitis, lung infection, sepsis, urinary tract infection, and syncope at 16.7% each among the top serious adverse event terms. The denominator and distribution by dose are not reported in the registry record.

Because the groups were sequential and not randomized controls, these counts do not establish comparative risk. Small group sizes and the absence of uncertainty intervals also limit precision. The counts describe recorded events; they do not, alone, establish causality, severity beyond the serious classification, or clinical importance.

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

The results describe safety events recorded in four dose-escalation groups receiving NKTR-255 with cetuximab. They show that serious adverse events and other adverse events were recorded among participants in these groups, and that deaths were listed in each group. The registry also identifies several serious adverse event terms with their reported percentages. These observations are relevant to understanding what was recorded during this study, but the available details do not provide a complete clinical account of each event.

They do not show that NKTR-255 or cetuximab caused any particular event. The record does not report treatment attribution for the listed serious events or deaths. It also does not give detailed outcome, timing, or event-level data. Nor do the counts establish that one dose is safer or less safe than another: the groups were sequential rather than randomized, and their sizes differ. A numerical contrast between groups would not remove those design limitations.

The safety results do not answer whether the combination is effective, and the registry entries available in the registry record include no efficacy results. They also do not establish a recommended dose, despite the arm description's stated purpose of establishing the RP2D. A dose-selection conclusion would require the relevant protocol and full analysis details, which are not reported in the registry record.

In general, an absence of a reported analysis is not evidence that no events occurred; it means the registry information does not present that analysis. The appropriate interpretation is therefore bounded: these counts characterize recorded events in the listed groups, while causal attribution, comparative safety, precision, and efficacy remain unresolved in the record.

13. Why This Trial Matters Statistically

Early-phase dose escalation raises statistical questions that differ from a conventional randomized comparison. The central task is to describe safety across successive dose groups and use the observed information to guide further study. Here, the record names establishing the RP2D as the purpose of the combination dose escalation, but does not report the escalation rules, the dose-selection analysis, or the decision reached. That distinction matters: an intended objective is not itself a reported result.

Small sequential groups can make descriptive summaries useful while leaving substantial uncertainty about how well they represent broader patient populations. A count such as participants with a serious adverse event is readily interpretable, but does not isolate the role of dose when group membership was not randomized. It also does not substitute for detailed timing, attribution, event severity, or follow-up information.

The registry record offers a reminder that safety reporting has multiple layers. A headline count, a list of event terms, the defined analysis population, the follow-up period, and an analysis plan answer different questions. If some of these details are unavailable, readers should resist treating the count as a complete estimate of risk or as evidence for a causal comparison. The top serious-event terms provide additional context but, without a stated denominator and group distribution, cannot be interpreted as dose-specific rates.

Statistically, the study's structure calls for cautious descriptive interpretation rather than ranking the doses. Clear reporting of participant flow, endpoint definitions, event attribution, uncertainty, and dose-selection methods would help readers understand how the recorded safety experience informed later development. Those details are not reported in the registry record, so the presented counts have a limited but still informative role: they document events recorded during dose escalation without resolving comparative or causal questions.

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 available safety information has important trial-specific limitations. The study is open-label and sequential, with allocation listed as not applicable. The registry explicitly states that the groups are not a like-for-like control comparison. Differences in event counts across dose levels therefore cannot be interpreted as randomized estimates of dose effects.

The groups are small: 7 participants were listed at each of the 1.5 µg/kg and 3.0 µg/kg levels, 6 at 4.5 µg/kg, and 3 at 6.0 µg/kg. Counts in groups of this size provide limited precision, and no confidence intervals are reported. The enrollment of 25 is the study-wide figure; the registry entries do not explain participant flow between the broader study and these dose groups.

The endpoint description includes more safety domains than the posted counts detail. Treatment relationship, adverse events leading to discontinuation, clinical laboratory abnormalities, and DLT results are not reported in the registry record. Deaths are listed, but their causes, timing, and relationship to treatment are not stated. The serious-event terms have percentages, but their denominator and distribution across dose groups are not specified.

The primary endpoint timeframe is stated, but detailed follow-up completeness and missing-data handling are not reported. The DLT population description is truncated at the timing anchor for its 21-day window. The registry also does not report the dose-escalation rules, the statistical analysis plan, a sample-size justification, or interim-analysis methods. These gaps limit interpretation of how the observed counts were assembled and how they informed dose selection.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Study of NKTR 255 in Combination With Cetuximab in Solid Tumors — NCT04616196.
• Registry record last updated 2025-06-08; status last verified 2025-05.
• Results first posted 2025-06-08.
• 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

The registry record describes a completed, open-label, multicenter Phase 1b/2 study of NKTR-255 as monotherapy or with cetuximab in solid tumors, including HNSCC and CRC. The combination dose-escalation arm description states that the purpose was to establish the RP2D. The record lists sequential design, no masking, enrollment of 25, and completion status.

The primary endpoint concerns treatment-emergent and serious adverse events during Phase 1b combination dose escalation in recurrent or refractory HNSCC or CRC. The posted group counts cover four NKTR-255 dose levels with cetuximab. They are descriptive and do not form a randomized comparison. The registry lists 2 outcome measures but no analyses. Detailed efficacy results, statistical analysis methods, missing-data procedures, event attribution, and the protocol's sample-size justification are not reported in the registry record.