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
HER2CLIMB was a randomized, parallel-group, quadruple-masked phase 2 trial comparing tucatinib with placebo, each given in combination with capecitabine and trastuzumab, in patients with advanced HER2-positive breast cancer.
| Feature | HER2CLIMB |
|---|---|
| Trial name | HER2CLIMB |
| ClinicalTrials.gov identifier | NCT02614794 |
| Phase | 2 |
| Status | Completed |
| Condition | HER2 Positive Breast Cancer |
| Enrollment | 612 |
| Allocation | Randomized |
| Design model | Parallel |
| Masking | Quadruple |
| Primary purpose | Treatment |
| Primary endpoint type | Time-to-event |
| Results posted | Yes |
| Outcome measures posted | 19 |
2. Clinical Question
The registered clinical question is whether adding tucatinib to capecitabine and trastuzumab differs from adding placebo to capecitabine and trastuzumab with respect to the trial's primary time-to-event endpoint in patients with advanced HER2-positive breast cancer.
Population
Patients with advanced HER2-positive breast cancer.
Intervention
Tucatinib in combination with capecitabine and trastuzumab.
Comparator
Placebo in combination with capecitabine and trastuzumab.
Primary question
Does the tucatinib-containing combination differ from the placebo-containing combination in progression-free survival as defined by the registry?
3. Trial Design
Tucatinib combination
- Tucatinib
- Capecitabine
- Trastuzumab
Placebo combination
- Placebo
- Capecitabine
- Trastuzumab
4. Trial Timeline
Trial start
The registered study start date was January 28, 2016.
Primary completion
The registered primary completion date was September 4, 2019.
Registry status
ClinicalTrials.gov lists the study status as completed.
5. Primary Endpoint
| Endpoint | Registered definition | Time frame | Type |
|---|---|---|---|
| Progression-free Survival (PFS) Per RECIST 1.1 as Determined by Blinded Independent Central Review (BICR) | Defined as the time from the date of randomization to the date of documented disease progression. | 34.6 months | Time-to-event |
The registry identifies this as the single primary endpoint. Its definition makes the analysis a time-to-event problem: each participant contributes follow-up from randomization, and the event of interest is documented disease progression.
The registry specifies RECIST 1.1 and blinded independent central review (BICR) as part of the endpoint definition.
6. Statistical Methodology
Time-to-event analysis
Because the primary endpoint is time-to-event, an appropriate statistical analysis must account for both the timing of documented progression and participants who have not experienced progression by the end of their available follow-up. A standard framework is survival analysis rather than a simple comparison of proportions.
Kaplan-Meier estimation
A Kaplan-Meier estimator can describe the distribution of progression-free survival over time. Participants who have not experienced documented progression during the period in which they are observed can contribute censored follow-up rather than being treated as if they had experienced the event.
Here, di represents the number of events at an event time and ni represents the number at risk immediately before that time.
Group comparison
For two randomized groups with a time-to-event primary endpoint, a log-rank test is commonly used to compare event-time distributions. A Cox proportional-hazards model is commonly used when a hazard ratio is the chosen measure of relative treatment effect.
RECIST 1.1 and BICR
The endpoint is defined using RECIST 1.1 and blinded independent central review. This is important statistically because progression is not simply a subjective declaration made after observing the treatment assignment; the registered endpoint specifies a standardized response framework and blinded central assessment.
Randomization
Randomization creates the basis for comparing the two treatment strategies without relying solely on observational adjustment. In a randomized parallel-group trial, the treatment assignment is the defining comparison for the primary efficacy analysis.
7. Planned Analysis
The registry identifies progression-free survival per RECIST 1.1 as determined by BICR as the primary endpoint and specifies a 34.6-month time frame. For an endpoint of this type, an appropriate formal analysis would normally estimate the progression-free survival distribution with a Kaplan-Meier method and compare randomized treatment groups with a time-to-event test such as the log-rank test. A Cox proportional-hazards model may be used to estimate a hazard ratio and its confidence interval when its assumptions are appropriate.
Those methods describe how the endpoint can be analyzed; they do not supply an observed treatment effect. Because the ClinicalTrials.gov record contains no formal statistical analyses, this page does not infer or reconstruct an outcome from other sources.
8. Safety Results
The ClinicalTrials.gov record includes serious adverse events by arm. These figures are reported as affected patients divided by patients at risk.
| Treatment group | Serious adverse events | At risk |
|---|---|---|
| Tucatinib + capecitabine + trastuzumab | 124 | 404 |
| Placebo + capecitabine + trastuzumab | 62 | 197 |
The ClinicalTrials.gov record therefore report 124/404 patients with serious adverse events in the tucatinib-containing group and 62/197 in the placebo-containing group.
These are descriptive safety counts, not a formal causal comparison. The denominators identify the patients at risk for the reported safety measure, while the numerator identifies those affected. Without a the ClinicalTrials.gov record, this page does not attach a p-value, confidence interval, risk ratio, or odds ratio to the serious-adverse-event comparison.
Safety and efficacy also answer different questions. A serious-adverse-event frequency describes an important aspect of tolerability; it does not directly determine the effect of treatment on progression-free survival.
9. Statistical Methods Explained
Why is this endpoint analyzed as time-to-event data?
Progression-free survival records not only whether documented progression occurs but also when it occurs after randomization. Participants can therefore have different amounts of follow-up, making survival-analysis methods more appropriate than a simple binary comparison at a single time point.
Why does the registry specify RECIST 1.1?
RECIST 1.1 provides a standardized framework for evaluating tumor response and progression. Using a prespecified response framework helps make the definition of disease progression more reproducible across participants and assessments.
Why was blinded independent central review specified?
BICR is relevant because knowledge of treatment assignment can influence assessment of disease status. A blinded central review process is intended to reduce the potential for assessment bias when determining progression.
What does randomization contribute statistically?
Randomization establishes the treatment groups before outcomes are observed. In expectation, this balances measured and unmeasured baseline factors across groups, allowing differences in outcomes to be interpreted as differences associated with the randomized treatment strategies under the trial's assumptions.
Why would a Kaplan-Meier curve be useful?
A Kaplan-Meier curve shows the estimated probability of remaining free of the event over time. It also makes the timing of events and the amount of censoring visible in a way that a single summary statistic cannot.
What would a hazard ratio mean if one were reported?
A hazard ratio below 1 would indicate a lower estimated instantaneous event rate in the treatment group relative to the comparator under the fitted model. It would not mean that the same percentage of participants avoided progression, nor would it directly equal a relative risk or absolute risk reduction.
Why is the confidence interval important?
A confidence interval communicates statistical uncertainty around an estimated treatment effect. A narrow interval indicates greater statistical precision than a wide interval, but the interval does not describe the range of individual patient outcomes.
10. Primary Endpoint Interpretation Framework
What the endpoint measures
The registered endpoint measures the time from randomization to documented disease progression under the RECIST 1.1 and BICR framework.
What it does not measure
PFS is not the same as overall survival, response rate, or a patient's subjective assessment of clinical benefit.
Why censoring matters
Participants may have incomplete event information at the end of available follow-up. Survival methods account for this through censoring rather than automatically treating incomplete observations as events.
Why BICR matters
The registry specifically identifies blinded independent central review, making the assessment process part of the endpoint definition rather than an incidental methodological detail.
11. Analysis Population and Interpretation
The ClinicalTrials.gov record establishes enrollment of 612 participants and a randomized, two-arm parallel design, but they do not provide the numerical statistical-analysis populations used for the posted efficacy results.
| Question | What the ClinicalTrials.gov record establishes |
|---|---|
| How many participants enrolled? | 612 |
| How many arms? | 2 |
| Was allocation randomized? | Yes |
| Was the design parallel? | Yes |
| Was the study masked? | Yes; quadruple masking |
| What was the primary endpoint? | Progression-free survival per RECIST 1.1 as determined by BICR |
| Was it a time-to-event endpoint? | Yes |
| Were results posted? | Yes |
| Were formal statistical analyses reported in the ClinicalTrials.gov record? | No; no formal statistical analyses were posted |
12. Design Topics
Randomization
The trial used randomized allocation. For a parallel-group comparison, randomization is the principal design mechanism supporting an unbiased comparison of the treatment strategies, subject to adherence to the assigned intervention and other assumptions required for causal interpretation.
Quadruple masking
The registry identifies the study as quadruple masked. Masking can reduce the risk that knowledge of assignment influences treatment administration, outcome assessment, participant behavior, or other trial processes, depending on which parties are covered by the masking specification.
Parallel-group structure
The parallel design means participants are assigned to one of the two treatment strategies rather than being sequentially exposed to both randomized strategies as in a crossover design. The ClinicalTrials.gov record does not identify a crossover component.
Non-inferiority margin
The ClinicalTrials.gov record does not specify a non-inferiority design or a non-inferiority margin. Accordingly, no non-inferiority interpretation is made here.
Factorial design
The ClinicalTrials.gov record identifies a parallel two-arm design rather than a factorial design. No factorial treatment structure is reported in the ClinicalTrials.gov record.
Bayesian methods
The ClinicalTrials.gov record does not identify a Bayesian primary analysis. No posterior probability, prior distribution, or Bayesian decision rule is therefore reported.
Missing-data and imputation methods
The ClinicalTrials.gov record does not specify an imputation strategy for missing efficacy measurements. For a time-to-event endpoint, censoring rules are an important component of the statistical analysis, but the ClinicalTrials.gov record does not provide the detailed censoring or missing-data rules beyond the registered endpoint definition.
13. Statistical Interpretation vs Clinical Interpretation
Statistical interpretation
The registered primary endpoint is a time-to-event measure. A formal comparison would require analysis of the timing of documented progression while accounting for censoring. The ClinicalTrials.gov record does not provide the formal comparative estimates.
Clinical interpretation
The trial directly compares a tucatinib-containing regimen with a placebo-containing regimen in advanced HER2-positive breast cancer. The ClinicalTrials.gov record establishes the treatment contrast and endpoint, but not the numerical magnitude of the primary efficacy effect.
The record supports a clear description of the randomized trial design, treatment comparison, masking, enrollment, primary endpoint, time frame, and reported serious-adverse-event counts. It does not support stating a numerical PFS hazard ratio, confidence interval, or p-value because those values are not present in the posted results.
14. Limitations
- Incomplete numerical results: the ClinicalTrials.gov record states that results were posted but provide no entries in the statistical-analysis field.
- No reconstructed effect estimate: this page does not infer a hazard ratio, p-value, confidence interval, median PFS, event count, or other efficacy statistic from information outside the ClinicalTrials.gov record.
- Limited endpoint detail: the registry definition identifies progression-free survival and its assessment framework, but the ClinicalTrials.gov record does not provide the complete statistical-analysis specification.
- Safety denominators differ from total enrollment: the registry-reported serious-adverse-event data use arm-specific populations of 404 and 197 at risk rather than the overall enrollment count of 612.
- No subgroup estimates reported: the ClinicalTrials.gov record does not provide subgroup hazard ratios or interaction tests, so no subgroup treatment-effect interpretation is presented.
- No interim-analysis information reported: the ClinicalTrials.gov record does not identify an interim-analysis schedule, stopping boundary, or alpha-spending procedure.
- No multiplicity strategy reported: the registry data do not specify an alpha hierarchy or multiplicity-adjustment method for the primary and secondary endpoints.
- No missing-data strategy reported: detailed rules for censoring, missing assessments, or imputation are not included in the ClinicalTrials.gov recordset.
- External generalizability: the ClinicalTrials.gov record identifies advanced HER2-positive breast cancer as the condition but does not provide a detailed baseline-characteristics table from which broader generalizability could be assessed.
15. Why This Trial Matters Statistically
HER2CLIMB is a useful teaching example because its registry structure brings several core clinical-trial concepts together without requiring the reader to begin with a complicated statistical model.
| Concept | How it appears in HER2CLIMB |
|---|---|
| Randomization | Participants were assigned using randomized allocation. |
| Parallel-group design | The trial has 2 parallel arms. |
| Blinding | The registry identifies quadruple masking. |
| Time-to-event analysis | The primary endpoint is progression-free survival. |
| RECIST 1.1 | Progression is defined within the registered RECIST 1.1 framework. |
| Central review | The primary endpoint specifies blinded independent central review. |
| Censoring | Time-to-event analysis requires appropriate handling of participants without documented progression during available follow-up. |
| Hazard ratio interpretation | A hazard ratio would provide a relative time-to-event measure if reported by the formal analysis. |
| Confidence intervals | Confidence intervals would quantify uncertainty around an estimated treatment effect. |
| Safety analysis | Serious adverse events are reported by treatment group using affected and at-risk counts. |
16. Related Tutorials
Learn more about the methods used in this trial:
17. Related Statistical Calculators
18. Sources
- ClinicalTrials.gov: HER2CLIMB, NCT02614794.
- PubMed: Publication associated with HER2CLIMB.
- PubMed: Publication associated with HER2CLIMB.
- PubMed: Publication associated with HER2CLIMB.
- PubMed: Publication associated with HER2CLIMB.
- PubMed: Publication associated with HER2CLIMB.
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19. Record Summary
HER2CLIMB is a completed randomized phase 2, parallel-group, quadruple-masked clinical trial enrolling 612 participants with advanced HER2-positive breast cancer. The registered intervention is tucatinib in combination with capecitabine and trastuzumab, compared with placebo in combination with capecitabine and trastuzumab. Its single registered primary endpoint is progression-free survival per RECIST 1.1 as determined by blinded independent central review, defined as the time from randomization to documented disease progression over a 34.6-month time frame.
The ClinicalTrials.gov record confirms that results were posted, but it does not contain a formal statistical-analysis entry with the numerical efficacy estimates needed to report a primary PFS hazard ratio, confidence interval, p-value, median, or event count. The ClinicalTrials.gov record can be reported directly: serious adverse events affected 124 of 404 patients at risk in the tucatinib-containing group and 62 of 197 patients at risk in the placebo-containing group.