This page provides an independent statistical analysis and educational interpretation of publicly reported results. ClinicalTrials.gov provides the official trial registry record. Numerical trial results on this page are restricted to the results posted in the ClinicalTrials.gov record; calculations added by Clinical Biostats are labelled as such.
1. Trial at a Glance
This page covers the registry results for UK Ibrance Patient Program (IPP) Study (NCT03921866), a registered phase not stated study. The primary outcome is Percentage of Participants According to Treatment Lines.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT03921866 |
| Phase | Phase not stated |
| Condition | HR+/HER2- Locally Advanced, Metastatic Breast Cancer |
| Allocation | Not Stated |
| Design model | Not Stated |
| Masking | Not Stated |
| Enrollment | 191 |
| Arms in the primary outcome | n/a |
| Lead sponsor | Pfizer |
| Results posted | Yes |
2. Clinical Question
Population
Patients in the United Kingdom with hormone receptor-positive, HER2-negative metastatic breast cancer who were enrolled in the Ibrance Patient Program. The study population was defined through eligible participants’ medical records extracted for the study. The registry reports an enrollment of 191 participants.
Intervention
Palbociclib treatment as part of the United Kingdom Ibrance Patient Program. The study describes real-world treatment patterns, patient characteristics, clinical outcomes, and healthcare resource utilisation associated with treatment.
Comparator
No randomized comparator is stated. This is an observational cohort, and the registry record does not describe a like-for-like control group. The results therefore concern the recorded cohort rather than a comparative estimate of treatment effects.
Primary question
How were participants distributed across treatment lines at baseline, considering treatment between breast cancer diagnosis and the index date? The registry defines categories for palbociclib as first-line treatment, palbociclib added to ongoing letrozole, and palbociclib prescribed as second-line or later treatment. The numerical percentages for these categories are not reported in the registry record.
The broader study question concerns real-world treatment patterns and outcomes in the three years following palbociclib initiation. The listed secondary outcomes cover dose and treatment patterns, discontinuation, and subsequent treatment lines. The registry record describes these aims but does not report numerical results for the primary endpoint in the available information. The study can therefore be read as a descriptive account of treatment use in an enrolled program cohort, not as a randomized comparison of palbociclib with another treatment.
3. Trial Design
This was an observational cohort study of patients with hormone receptor-positive, HER2-negative metastatic breast cancer treated with palbociclib through the United Kingdom Ibrance Patient Program. The registry lists Pfizer as the sponsor, an enrollment of 191, and a completed status. The study start date is 2019-03-01, and the primary completion date is 2021-03-04.
The primary outcome is the percentage of participants according to treatment lines at baseline. Its definition concerns treatment between breast cancer diagnosis and the index date. The categories distinguish palbociclib prescribed as first-line treatment for metastatic breast cancer, palbociclib added to ongoing letrozole prescribed more than 3 months before palbociclib initiation, and palbociclib prescribed as second-line or later treatment. The registry record does not report the percentage in each category.
The study also lists secondary outcomes concerning starting dose, endocrine therapy alongside palbociclib, dose reductions, treatment discontinuation and reasons for discontinuation, temporary discontinuation, time to dose reduction in first-line therapy, time to palbociclib discontinuation, and treatment lines after progression. The record lists 90 outcome measures but no analyses. Numerical results for these outcomes are not reported in the registry record.
Because the record describes an observational cohort and does not state a randomized allocation or a control arm, the design is descriptive rather than a randomized treatment comparison. The enrollment number describes the registered cohort; it does not establish how many participants contributed data to each individual outcome. Outcome-specific analysis populations and denominators 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
| Stage | Palbociclib |
|---|---|
| STARTED | 191 |
| COMPLETED | 191 |
| NOT COMPLETED | 0 |
Analysis population for the primary outcome, as defined in the registry: FAS comprised of medical records extracted for the purpose of the study from all eligible participants who were enrolled into the study.
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: The full analysis set (FAS) comprised of medical records extracted for the purpose of the study from all eligible participants who were enrolled into the study.
| Characteristic | Unit | Palbociclib |
|---|---|---|
| Participants analysed | 191 | |
| Age, Continuous | Years | 57.6 (SD 12.8) |
| Sex: Female, Male: Female | Participants | NA |
| Sex: Female, Male: Male | Participants | NA |
| Race/Ethnicity, Customized: White | Participants | 169 |
| Race/Ethnicity, Customized: Black | Participants | 8 |
| Race/Ethnicity, Customized: Asian | Participants | 1 |
| Race/Ethnicity, Customized: Other | Participants | 1 |
| Race/Ethnicity, Customized: Missing | Participants | 12 |
6. Primary Endpoint
The registry lists the primary outcome as Percentage of Participants According to Treatment Lines, measured over At baseline.
| Element | Registry entry |
|---|---|
| Result type | Number |
| Measure of spread | not applicable |
| Unit | Percentage of participants |
| Endpoint classification | Binary Endpoint |
The primary endpoint is the percentage of participants in each treatment-line category at baseline. It describes where palbociclib fit into participants’ treatment history between breast cancer diagnosis and the index date. The registry defines categories for palbociclib as first-line treatment for metastatic breast cancer, as first-line treatment added to ongoing letrozole, and as second-line or later treatment.
A percentage is a descriptive measure of how participants are distributed across defined categories. In this observational study, it can help characterize treatment use in the enrolled program cohort. It does not, by itself, estimate a causal treatment effect or compare outcomes under alternative treatment strategies.
The registry states the outcome’s timeframe as baseline, but numerical percentages for the categories are not reported in the registry record. The record also does not report category-specific participant counts or the denominator used for each percentage. Without those results, the endpoint’s observed distribution and its precision cannot be assessed. The outcome definition explains what was to be described; it does not establish what the cohort’s treatment-line pattern was.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry record identifies a completed observational cohort with 191 enrolled participants and a primary outcome describing treatment lines at baseline. However, the numerical result for that outcome is not reported in the registry record. The category definitions are available, but there are no percentages or participant counts for the individual categories in the information recorded. Consequently, the treatment-line distribution cannot be characterized from the endpoint definition alone.
The same distinction applies to the broader study aims. The record asks about treatment patterns, patient characteristics, clinical outcomes, and healthcare resource utilisation during the three years following palbociclib initiation. It also lists secondary outcomes covering dosing, endocrine therapy, dose reduction, discontinuation, and treatment after progression. These are outcome topics, not results. Their numerical findings are not reported in the registry record.
The registry lists 90 outcome measures and no analyses. That does not establish whether analyses were conducted outside the record; it means that the posted information does not specify their methods or results. In particular, the record does not report estimates of uncertainty, such as confidence intervals, for the primary endpoint. A confidence interval generally describes the range of values compatible with an estimate under a specified statistical model; without a reported estimate and interval, the endpoint’s precision cannot be evaluated.
The design also limits the kind of interpretation available. This is an observational cohort, not a randomized comparison, and the registry does not state a like-for-like control group. Descriptive patterns in enrolled participants cannot, on their own, separate treatment-related differences from differences in patient characteristics, prior treatment, or clinical circumstances. The information recorded does not establish how those factors were handled analytically.
Safety information is listed for palbociclib, including 54 participants affected in the serious adverse-event category, 116 in the other adverse-event category, and 3 deaths. These figures describe the registry’s recorded group-level counts, but the record excerpt does not provide event-level timing, participant-level overlap, or a causal assessment. The listed serious terms include neutropenia, diarrhoea, and other, with percentages recorded for each term. These data should be read as descriptive reporting, not as evidence that palbociclib caused any particular event.
Overall, the record supports an understanding of the study’s cohort, objectives, endpoint definitions, and some adverse-event counts. It does not provide the primary endpoint results or enough analytic detail to estimate comparative effects, assess endpoint precision, or attribute outcomes to treatment.
9. Statistical Methods Explained
For an observational cohort, a percentage endpoint is a descriptive statistic: it expresses how participants fall into defined categories within the study population. The primary endpoint’s categories concern the place of palbociclib in the treatment history at baseline. General statistical interpretation depends on both the numerator, the number of participants in a category, and the denominator, the participants included in the relevant analysis. The registry record does not report the category counts, percentages, or outcome-specific denominators, so those quantities cannot be assessed.
What does a percentage describe?
In general, a percentage describes a proportion within a stated population. Its interpretation relies on a clear definition of who is included and what qualifies for the category. For this endpoint, the registry gives the treatment-line definitions and describes the study population as eligible participants whose medical records were extracted for the study. It does not state whether every enrolled participant contributed to every endpoint or how missing records were handled. Therefore, enrollment of 191 should not automatically be treated as the denominator for each result.
Categories can be useful for describing treatment patterns, but their meaning depends on how they are operationalized. The registry specifies that the first-line palbociclib-with-letrozole category involves ongoing letrozole prescribed more than 3 months before palbociclib initiation. It also defines second-line treatment as second-line or later treatment for metastatic breast cancer. The record does not provide further rules for classifying cases that might not fit the stated descriptions, nor does it report how such cases were handled.
What would uncertainty measures add?
General statistical practice often pairs a percentage with an uncertainty interval. A confidence interval conveys the sampling uncertainty associated with an estimate under the assumptions of a statistical method. It does not describe every source of uncertainty: for example, it cannot by itself correct unclear outcome definitions, incomplete records, or selection into an observational program. No confidence interval for the primary endpoint is reported in the registry record, and the endpoint result itself is not reported. Its magnitude and precision therefore cannot be judged from the record.
The registry lists no analyses. It does not report a statistical model, a method for estimating uncertainty, or adjustments for participant characteristics. These details should not be inferred from the fact that the study is observational or from the endpoint wording. General methods such as regression adjustment may be used in observational research, but the registry record does not state that such methods were used for this study.
Why does the observational design matter?
In general, observational studies describe outcomes among people whose care was not assigned through a stated randomized comparison. Treatment patterns can reflect clinical decisions and participant characteristics. Consequently, a difference between groups, if one were reported, would not necessarily represent a treatment effect. In this cohort, the registry does not describe a randomized comparator, and the listed intervention is palbociclib. The record therefore does not support a randomized treatment contrast.
The primary endpoint is descriptive and does not require a comparative interpretation to be meaningful: it could show how treatment lines were distributed in the cohort if its results were reported. But without the percentages, counts, and analysis population, even that descriptive interpretation remains unavailable. The endpoint definition alone cannot tell whether first-line or later-line use was more common.
How should planning calculations be read?
General sample-size calculations estimate what amount of information might be needed under specified assumptions to detect a chosen effect with a chosen statistical criterion. The registry record’s planning illustration is described as using a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation, with the target effect expressed as a fraction of the observed effect. For time-to-event outcomes, the illustration is described as reporting a total number of events; for other outcomes, it is described as participants per arm.
Those are planning assumptions, not evidence about the study’s observed design or outcomes. The registry describes this illustration as computed from the observed effect, not as the study’s own design. Any sample-size figures from such an illustration should therefore be understood as planning quantities, never as observed power or proof that the study was adequately powered. This cohort is not described as a two-arm randomized comparison, so a two-arm planning framework should not be mistaken for the cohort’s design.
More generally, statistical significance and practical importance are distinct concepts. A small p-value, when reported, addresses compatibility with a specified null model under assumptions; it does not establish causality or determine the importance of an outcome. No p-value or analysis result for the primary endpoint is reported in the registry record. Since the endpoint’s estimate is also absent, there is no basis for judging its size, direction, statistical significance, or precision.
10. Multiplicity, Missing Data and Analysis Populations
The registry lists 90 outcome measures and no analyses. It does not report how outcomes were prioritized beyond identifying the treatment-line percentage as primary, whether statistical tests were conducted, or whether any adjustment for multiple comparisons was used. When many outcomes are tested, general statistical practice considers the possibility that some apparently notable findings may arise by chance. The record does not describe a multiplicity strategy, so no claim about such adjustment can be made.
Missing-data procedures are also not reported in the registry record. The study population is described as eligible participants with medical records extracted for the study, but the record does not state how incomplete records, unavailable outcome information, or participants with no usable measurement were handled. It does not provide outcome-specific denominators or describe whether data were excluded, imputed, or otherwise addressed. These details matter because a percentage can be difficult to interpret if the population contributing data is unclear.
The analysis population is described as the FAS, comprising medical records extracted for the study from all eligible participants enrolled. The record does not provide a numerical count for this population distinct from the enrollment of 191, nor does it establish that the same population was used for every outcome. There is no reported account of deviations from the defined population or reasons for any exclusions.
Accordingly, neither the impact of missing data nor the robustness of results to analytic choices can be evaluated from the registry record. These are reporting gaps, not evidence that data were missing or that a particular procedure was or was not performed outside the record.
11. Safety Results
The registry reports serious adverse events as affected participants divided by participants at risk.
| Arm | Participants with serious adverse events | Participants at risk | Percentage |
|---|---|---|---|
| Palbociclib | 54 | 191 | 28.3% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| Palbociclib | 3 of 191 |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 0% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| Palbociclib | 116 of 191 |
Most frequent serious adverse event terms
| Event term | Organ system | Palbociclib |
|---|---|---|
| Neutropenia | Blood and lymphatic system disorders | 53 of 191 |
| Diarrhoea | Gastrointestinal disorders | 1 of 191 |
| Other | Gastrointestinal disorders | 1 of 191 |
Most frequent non-serious adverse event terms
| Event term | Organ system | Palbociclib |
|---|---|---|
| Neutropenia | Blood and lymphatic system disorders | 90 of 191 |
| Nausea | Gastrointestinal disorders | 24 of 191 |
| Diarrhoea | Gastrointestinal disorders | 22 of 191 |
| Other | Gastrointestinal disorders | 18 of 191 |
| Vomiting | Gastrointestinal disorders | 13 of 191 |
Serious events with the highest arm-level rate: neutropenia (27.7%), diarrhoea (0.5%), other (0.5%).
The registry lists a palbociclib group with 191 participants at risk for serious adverse events and 54 affected. It also lists 191 at risk and 116 affected in the other adverse-event category, along with 3 deaths. These are counts as recorded; they should not be converted into a causal conclusion. The registry record does not describe whether the same participants could appear in both adverse-event categories, nor does it provide timing or event-level detail for these group counts.
The listed serious adverse-event terms include neutropenia at 27.7%, diarrhoea at 0.5%, and other at 0.5%. The record does not give accompanying term-specific participant counts in the information, or explain the denominator and coding details for each listed percentage. These percentages should therefore be read as registry-reported descriptions of serious terms, not as a complete safety profile or a comparison with an untreated group.
The 3 deaths are reported as a count, but the registry record does not state whether they were judged related to palbociclib or provide causes. The figures do not establish that treatment caused an adverse event or death. They describe recorded events in the cohort; attribution and comparative risk are not reported.
12. What the Result Does, and Does Not, Mean
The study addresses a practical descriptive question: how palbociclib was used among United Kingdom patients with hormone receptor-positive, HER2-negative metastatic breast cancer enrolled in the Ibrance Patient Program. The registry identifies the population, intervention, primary endpoint, and a broad set of secondary outcome topics. Its enrollment of 191 gives the size of the registered cohort, while the endpoint definitions explain what the investigators intended to characterize.
What the record does not establish is the actual distribution of participants across treatment lines. Numerical results for the primary endpoint are not reported in the registry record. Nor are numerical results reported for the listed secondary outcomes in the registry record recorded. Thus, the objective and definitions should not be mistaken for observed findings.
The observational design also means that the study is not described as a randomized comparison. Without a stated comparator and reported analytic methods, the record cannot establish what would have happened to similar participants under a different treatment. Even a reported pattern of outcomes within this cohort would not, by itself, show that palbociclib caused those outcomes.
The adverse-event figures provide counts for participants affected in the serious and other categories, a death count, and percentages for selected serious terms. They do not provide a causal assessment or enough detail to compare event risks across treatments. Their interpretation is descriptive and bounded by the reporting detail available.
In short, the registry record identifies a completed real-world cohort study and makes its principal descriptive question clear. It does not provide the primary endpoint results, the uncertainty around those results, or enough methods information to make stronger comparative claims. The appropriate reading is therefore about the study’s scope and reporting, rather than a conclusion about treatment efficacy or safety.
13. Why This Trial Matters Statistically
Real-world observational cohorts can document how a treatment is used in a defined care program and can identify questions that matter beyond a tightly controlled comparison. This study’s stated scope includes treatment patterns, patient characteristics, clinical outcomes, and healthcare resource utilisation in United Kingdom patients treated with palbociclib. Its secondary outcome topics include starting dose, endocrine therapy alongside palbociclib, dose changes, discontinuation, and later treatment lines. Those domains can help frame what a fuller account of treatment experience would describe.
Statistically, the registry also illustrates why outcome definitions and numerical results need to be read separately. The primary endpoint is defined by treatment-line categories and a baseline timeframe, but its percentages are not reported in the registry record. A clear definition is necessary for interpretation, yet it cannot replace the observed counts, denominators, and uncertainty estimates that allow readers to judge the result.
The design is important to that reading. An observational cohort can describe patterns in its enrolled population, but the registry does not state a randomized comparator. Statistical descriptions of treatment use should therefore not be interpreted as randomized evidence of comparative effects. The absence of reported analyses and uncertainty measures further limits assessment of precision and of how patient characteristics were considered.
The record’s value is consequently in defining a real-world research question and showing the intended breadth of measurement. Its limitations are equally instructive: registration details and endpoint plans do not, on their own, communicate the resulting evidence. For a statistical interpretation of the cohort’s outcomes, reported estimates, denominators, methods, and uncertainty would be needed.
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.
Several limitations specific to this record constrain interpretation. Although the study is marked completed and reports an enrollment of 191, numerical results for the primary treatment-line endpoint are not reported in the registry record. The record also lists 90 outcome measures but no analyses, and numerical results for the secondary outcomes are not reported in the information.
The registry does not report outcome-specific denominators, category counts for the primary endpoint, confidence intervals, or other measures of uncertainty for that endpoint. The analysis population is described as medical records extracted from eligible enrolled participants, but a distinct numerical count and outcome-by-outcome participation are not reported. Handling of missing or incomplete records is not reported in the registry record.
The observational cohort is not described as a randomized comparison, and the record does not state a like-for-like control group. Statistical adjustment methods and a detailed analysis plan are not reported. As a result, the record cannot support a comparative causal interpretation, and the extent to which patient characteristics were accounted for cannot be assessed.
Safety reporting is also limited in the available information. Counts are recorded for participants affected in the serious and other adverse-event categories, and deaths are counted, but event timing, overlap between categories, causes of death, and causal attribution are not reported. The listed percentages for serious terms are not accompanied by detailed denominators in the record excerpt. These limitations concern what is reported; they do not establish what analyses or additional information may exist elsewhere.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: UK Ibrance Patient Program (IPP) Study — NCT03921866.
- Registry record last updated 2023-03-17; status last verified 2022-06.
- Results first posted 2023-03-17.
- 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.
Continue through the Clinical Biostats statistical pathway
Use this trial's endpoint as a starting point for deeper study of effect measures, confidence intervals, and sample-size planning.
18. Record Summary
The United Kingdom Ibrance Patient Program study is a completed observational cohort of patients with hormone receptor-positive, HER2-negative metastatic breast cancer treated with palbociclib. The registry lists Pfizer as sponsor, an enrollment of 191, a start date of 2019-03-01, and a primary completion date of 2021-03-04.
The primary outcome is the percentage of participants according to treatment lines at baseline, covering treatment between breast cancer diagnosis and the index date. The registry record defines the categories but does not report their numerical percentages. It lists 90 outcome measures and no analyses; numerical results for the primary and secondary outcomes are not reported in the information.
The record also lists adverse-event counts and selected serious-event terms. These are descriptive reports and do not establish causal attribution. The observational design, unreported endpoint results, and limited analytic detail prevent assessment of treatment-line patterns, endpoint precision, or comparative effects from the registry information alone.