A Study of Palbociclib in Addition to Standard Endocrine Treatment in Hormone Receptor Positive Her2 Normal Patients With Residual Disease After Neoadjuvant Chemotherapy and Surgery: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for A Study of Palbociclib in Addition to Standard Endocrine Treatment in Hormone Receptor Positive Her2 Normal Patients With Residual Disease After Neoadjuvant Chemotherapy and Surgery (NCT01864746), a randomized phase 3 study. The primary outcome is Invasive Disease Free Survival (iDFS) for Palbociclib vs. Placebo in Patients With High CPS-EG Score After Neoadjuvant Chemotherapy Receiving Standard Adjuvant Endocrine Therapy for HR-positive/HER2-normal Primary Breast Cancer..

2. Clinical Question

The clinical question is therefore a comparison of treatment strategies against the same endocrine-therapy background. It concerns invasive disease-free survival, not simply tumor response after chemotherapy: the endpoint tracks time from randomization until a defined invasive recurrence, second primary cancer, or death event. The registry record identifies the intended population and endpoint, but it does not give results that allow the size or precision of a treatment-group difference to be judged. The question should be kept distinct from the safety counts, which describe adverse events and deaths without supplying an efficacy comparison.

3. Trial Design

PENELOPEB is registered as a Phase III, randomized, parallel-group study with quadruple masking. The sponsor is GBG Forschungs GmbH. The registry lists enrollment as 1250 and status as completed. The study start is recorded as 2013-10-30, and primary completion as 2020-08-24.

The comparison is palbociclib versus placebo, with standard adjuvant endocrine therapy as the background treatment. Palbociclib is described as 125 mg once daily for days 1 to 21, followed by 7 days off treatment in a 28-day cycle, for thirteen cycles. The placebo arm is described with the corresponding daily schedule and cycle pattern. The registry does not specify the endocrine regimens used or give further detail about their management.

The target population is described as pre- and postmenopausal women with HR-positive/HER2-normal primary breast cancer who remained at high risk of relapse after neoadjuvant taxane-containing chemotherapy. The brief summary specifies less than pathological complete response and a high CPS-EG score. These details define the setting to which the trial question applies; they do not establish that findings apply to other breast cancer groups or treatment settings.

Random assignment is intended to make treatment groups comparable on average, while masking can reduce the influence of treatment knowledge on care and outcome assessment. The registry labels masking as quadruple but does not identify which roles were masked. Allocation concealment procedures, stratification factors, and the statistical plan are not reported in the registry record. The record identifies an intention-to-treat population for the primary endpoint, but does not provide a participant-flow account or an efficacy analysis result.

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: Female patients \>=18 years with residual invasive disease after NACT (in breast or lymph nodes), centrally assessed ER+ and/or PgR+ and HER2- tumors and centrally assessed Ki-67 status and a CPS-EG score of \>=3 or 2 with ypN1 (after amendment 3, February 9, 2015) were eligible. \>=16weeks NACT (incl. 6 weeks taxane), surgery and radiation received.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Intention-to-treat 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 Invasive Disease Free Survival (iDFS) for Palbociclib vs. Placebo in Patients With High CPS-EG Score After Neoadjuvant Chemotherapy Receiving Standard Adjuvant Endocrine Therapy for HR-positive/HER2-normal Primary Breast Cancer., measured over From date of randomisation to data cut off: 24 August 2020 (approximately 6 years and 6 months).

The primary endpoint is invasive disease-free survival (iDFS), expressed in the registry as the percentage of patients without invasive disease. Its timeframe is from randomization to the data cut off on 24 August 2020, approximately 6 years and 6 months. The registry defines iDFS as the time until the first specified event: invasive recurrence in the same or opposite breast, locoregional or distant recurrence, death from breast cancer or another cause, death of unknown cause, invasive contralateral breast cancer, or a second primary invasive non-breast cancer. Assessment is described as continuing until the end of the study.

Time-to-event endpoints are used when the timing of an event matters and participants may have different durations of follow-up. A survival estimate can incorporate the timing of events and account for observations that end without a recorded event by the analysis cut off, subject to the analysis method and its assumptions. This makes iDFS broader than a simple count of recurrences: deaths and specified second cancers also qualify as events under this definition.

The registry lists a 95% confidence interval for the endpoint, but no category-specific estimates, confidence limits, or treatment comparison are available in the record summarized by the posted results. The endpoint definition identifies what is intended to be measured; it does not, on its own, show the observed treatment effect or its precision.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does randomization contribute?

In general, randomization assigns participants to treatment groups by chance. If allocation is implemented as intended, it can balance both measured and unmeasured prognostic factors across groups on average. This supports a fair comparison of outcomes. It does not guarantee that the groups will be identical, remove uncertainty, or protect against bias arising after assignment. The registry identifies the study as randomized and parallel-group, but allocation procedures, any stratification factors, and the method used to generate the sequence are not reported in the registry record.

What does masking mean?

In general, masking means that some people involved in a trial are not told which treatment a participant receives. It can limit changes in care, reporting, or assessment that might result from knowing the assignment. The record calls the study quadruple-masked, but does not say which participants, clinicians, investigators, or outcome assessors were masked. The label alone therefore does not reveal how masking was maintained or whether it remained effective.

Why use a time-to-event endpoint?

In general, time-to-event methods use both whether an event occurred and when it occurred. They can also use partial follow-up when a participant has no recorded event by the analysis cut off or leaves observation earlier, subject to the chosen method and assumptions. This is relevant to iDFS because the endpoint starts at randomization and ends at the first event in a defined set. The registry lists the event components and gives the data cut off as 24 August 2020, but does not report the analysis method, censoring rules, number of events, or estimates by arm. Those omissions prevent an independent appraisal of the time-to-event analysis.

How should a confidence interval be understood?

In general, a confidence interval expresses the uncertainty around an estimated quantity under a specified statistical procedure. A narrower interval indicates greater precision than a wider interval on the same scale, but an interval does not by itself establish clinical importance or prove that a result is free from bias. The registry names a 95% confidence interval for the primary endpoint, but does not report its limits or the corresponding estimates. Therefore, the precision of the trial's primary comparison cannot be read from the record.

What does intention-to-treat describe?

In general, an intention-to-treat analysis compares participants according to their randomized assignment, regardless of later treatment changes, when the analysis is conducted on that basis. This approach preserves the advantages of randomization and estimates the effect of assignment to a treatment strategy. The registry identifies the primary endpoint population as intention-to-treat, but does not provide a participant disposition, explain how missing endpoint information was handled, or state whether every randomized participant contributed to the reported analysis. No primary estimate is given to evaluate.

What is the role of the posted sample-size illustrations?

General planning calculations use assumptions to illustrate the size of a future study that might be needed to detect a specified effect with a chosen significance level and power. The record describes illustrations based on a fraction of the observed effect, a two-sided significance level of 0.05, equal allocation, and a normal approximation. For time-to-event outcomes, the description says the planning quantity is a total number of events; for other outcomes, it is participants per arm. These are planning illustrations, not observed power and not a substitute for the trial's own design rationale. The registry does not report the protocol's sample-size justification or its assumed target effect, and the posted efficacy information does not yield a single observed comparison on which to base an interpretation.

Why can over-dispersion matter?

General statistical explanation: some outcome models assume that variability follows a particular probability distribution. Over-dispersion occurs when the observed variability is greater than the model assumes. If it is ignored, standard errors and confidence intervals may be too optimistic, and tests may appear more decisive than warranted. The registry does not identify an over-dispersion issue or report an outcome model for the primary endpoint; this concept should not be taken as a description of the analysis actually used in PENELOPEB.

What can be learned from the safety counts?

In general, adverse-event counts describe events recorded under the trial's definitions and observation procedures. Their interpretation depends on the event definition, follow-up period, attribution rules, and whether the count refers to participants, events, or both. Here the record labels the figures as serious adverse events and gives at-risk and affected counts by group. It does not provide the full safety-analysis rules, duration of exposure, or details that would establish whether repeated events in one participant are counted separately. The listed figures can be reported as registry entries, but should not be expanded into assumptions about event rates or causality.

10. Multiplicity, Missing Data and Analysis Populations

The registry names iDFS as the primary endpoint and lists secondary outcomes of iDFS excluding second non-breast cancers, distant disease-free survival, and overall survival. It also indicates that the primary outcome has several categories or time points and is not reduced to one comparison. A collection of endpoints, time points, or subgroup comparisons can create a multiplicity issue: when many hypotheses are tested, the chance of at least one apparently notable result can increase. Trial protocols commonly address this through prespecified testing sequences or other adjustment strategies, but the statistical plan and any multiplicity control are not reported in the registry record.

The registry lists four outcome measures, while the available record does not set out the corresponding result details in a way that yields a single primary comparison. It reports zero analysis entries. That registry status does not establish that no analyses were conducted; it means the record does not present analysis entries to interpret. The order in which outcomes were tested, the prespecified hypotheses, and any handling of interim analyses are not reported in the registry record.

Missing data are also important for time-to-event outcomes. General methods may censor participants when follow-up ends without a recorded event, but that approach relies on assumptions about why observation ended. The record does not report the amount or pattern of missing endpoint information, reasons for loss to follow-up, censoring procedures, or sensitivity analyses. The primary population is identified as intention-to-treat, but the implementation details and analysis denominator are not reported. These gaps limit assessment of bias and robustness; they do not establish that missingness affected the result in a particular direction.

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 1% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: infections and infestations (4.1%), injury, poisoning and procedural complications (1.7%), overdose (1.1%), vascular disorders (0.9%), cellulitis (0.8%).

The registry reports serious adverse-event figures separately for palbociclib and placebo. In the palbociclib group, 64 of 633 at risk were affected; in the placebo group, 65 of 611 at risk were affected. These are the registry's group-level counts and denominators. They should be read as reported rather than converted into percentages or treated as a direct causal comparison. The record does not give the safety observation period or further definitions needed to evaluate differences in exposure.

The registry lists deaths as 63 in the palbociclib group and 67 in the placebo group. It does not specify in this summary the causes, timing, or relationship of these deaths to treatment. Deaths may also overlap with the primary endpoint's event definition, but the record does not provide participant-level linkage or an endpoint count that would establish how they overlap.

Among the serious adverse-event terms, the listed percentages are 4.1% for infections and infestations, 1.7% for injury, poisoning and procedural complications, 1.1% for overdose, 0.9% for vascular disorders, 0.8% for cellulitis, and 0.8% for nervous system disorders. These terms are reported in the record as the top serious terms; the available information does not specify all event categories or clarify whether the percentages refer to participants or events. The list is descriptive and should not be read as a complete safety profile or as evidence of treatment causation.

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

The registry record answers several design questions. It identifies a randomized, quadruple-masked, parallel-group Phase III comparison of palbociclib and placebo on a background of standard endocrine therapy. It describes a high-risk HR-positive/HER2-normal population after neoadjuvant taxane-containing chemotherapy and defines iDFS as the primary endpoint. It also records selected serious adverse-event counts and terms.

What the record does not establish is the size or direction of the primary treatment effect. No single iDFS estimate, confidence interval, or between-group test is reported in a form that can be interpreted as the primary comparison. Consequently, the record cannot show how large any difference was, how precise an estimate might be, or whether a statistical threshold was met. A planned endpoint is not a result, and a study's completion status does not supply the missing efficacy estimate.

The safety counts also have a limited meaning. They are recorded counts among the stated at-risk groups, with a selected list of serious event terms. Without fuller definitions, follow-up information, and attribution details, they do not establish that a treatment caused a particular event or that the listed terms exhaust the safety experience. The deaths recorded in the safety information cannot be treated as a treatment effect or as an iDFS comparison.

These limitations do not mean that the trial found no effect, nor do they mean that it found an effect. They describe what can and cannot be concluded from the registry record. A full interpretation of the research question would require the primary results and the analysis details, including estimates by group, uncertainty, event counts, follow-up handling, and the prespecified statistical approach. Without those, conclusions about efficacy or the comparative balance of benefits and harms are not supported by the posted information.

13. Why This Trial Matters Statistically

This trial is statistically important because it asks a focused comparative question in a clinically defined high-risk setting: whether adding palbociclib to standard endocrine therapy changes iDFS compared with placebo on the same background. Randomization and masking are design features intended to support a credible comparison, while the time-to-event endpoint reflects both whether and when invasive disease or another defined event occurs.

The endpoint definition also illustrates that a composite survival outcome depends on its components. Here iDFS includes invasive recurrence, specified second primary cancers, and death from several causes. This broad definition may capture clinically important events beyond recurrence alone, but it also means that an overall endpoint estimate would not, by itself, explain which component contributed most to any observed difference. Component-specific results would be needed to explore that question, and they are not reported in the registry record.

The trial also highlights why reporting is part of statistical interpretation. A protocol-level question and a carefully described endpoint do not allow readers to assess effect size without estimates and uncertainty. The lack of a single reported comparison leaves unanswered the practical statistical questions about precision, event timing, and the relationship between the primary and secondary outcomes. Likewise, the presence of a planning illustration cannot replace the trial's own design rationale or an observed result.

Thus, the registry record is informative about the intended design, population, intervention, comparator, and endpoint definition, but incomplete for evaluating the central treatment comparison. The distinction between a well-specified research question and a reported answer is essential: statistical credibility depends not only on design, but also on transparent results and analysis information.

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 main limitation for interpretation is the absence of a single reported primary efficacy comparison. The registry states that the primary outcome has several categories or time points and is not reduced to one comparison. It does not provide iDFS estimates by group, confidence-interval limits, event counts, or a test result. The effect's size and precision therefore cannot be evaluated from the posted results.

The statistical plan is not reported in the registry record. This includes the planned analysis model, handling of censoring, any interim analyses, multiplicity control, and the sample-size justification. The planning description refers to illustrations based on an observed effect, but does not establish the assumptions used in the trial's original design. Those illustrative calculations should not be interpreted as the trial's observed power.

The record identifies the primary population as intention-to-treat but does not provide participant flow, analysis denominators, or missing-data details. Enrollment is listed as 1250, while separate denominators appear in the safety record; the registry does not explain their relationship. The safety information also omits the observation period and further definitions needed to interpret the affected counts, deaths, and listed serious-event percentages.

The available description is specific to pre- and postmenopausal women with HR-positive/HER2-normal primary breast cancer, high relapse risk, residual disease after neoadjuvant taxane-containing chemotherapy, and a high CPS-EG score. Findings, if interpreted from a complete report, would need to be considered in that context rather than assumed to apply to populations not described in the record. The registry's description of quadruple masking does not identify who was masked, and allocation procedures are not reported. These are limits of the available record, not proof that the trial lacked procedures or analyses.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: A Study of Palbociclib in Addition to Standard Endocrine Treatment in Hormone Receptor Positive Her2 Normal Patients With Residual Disease After Neoadjuvant Chemotherapy and Surgery — NCT01864746.
• Registry record last updated 2023-12-12; status last verified 2023-11.
• Results first posted 2023-12-12.
• 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

PENELOPEB (NCT01864746) is registered as a completed Phase III randomized, parallel-group, quadruple-masked study sponsored by GBG Forschungs GmbH. It enrolled 1250 and compared palbociclib with placebo alongside standard adjuvant endocrine therapy in a high-risk HR-positive/HER2-normal breast cancer population after neoadjuvant chemotherapy. Palbociclib is described as 125 mg daily on days 1 to 21, followed by 7 days off in a 28-day cycle for thirteen cycles.

The primary endpoint is iDFS, defined from randomization to the first of specified invasive disease, second cancer, or death events, with the reported timeframe ending at the 24 August 2020 data cut off. The primary population is identified as intention-to-treat. The record lists secondary outcomes of iDFS excluding second non-breast cancers, distant disease-free survival, and overall survival.

Although selected safety counts and serious adverse-event terms are reported, the registry does not give a single interpretable primary efficacy comparison or the statistical details needed to assess it. The clinical question is clear; its answer cannot be determined from the posted results.