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 Real-world Treatment Patterns and Effectiveness of Palbociclib and AI Therapy (NCT04176354), a registered phase not stated study. The primary outcome is Real-World Progression Free Survival (rwPFS): Using Kaplan-Meier Method.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT04176354 |
| Phase | Phase not stated |
| Condition | Metastatic Breast Cancer |
| Allocation | Not Stated |
| Design model | Not Stated |
| Masking | Not Stated |
| Enrollment | 813 |
| Arms in the primary outcome | n/a |
| Lead sponsor | Pfizer |
| Results posted | Yes |
2. Clinical Question
Population
Adults with metastatic breast cancer who began first-line therapy in the Flatiron Health Analytic Database. The study summary describes the target population as people with HR+/HER2- metastatic breast cancer treated in US clinical practices.
Intervention
Palbociclib combined with an aromatase inhibitor as first-line therapy. The registry also names palbociclib plus letrozole as a treatment group.
Comparator
Letrozole as first-line therapy is listed as a treatment group. This is an observational comparison, not a randomized, like-for-like control comparison; allocation is not stated.
Primary question
What is the median real-world progression-free survival, measured from the start of first-line palbociclib plus an aromatase inhibitor to progression, death, or the specified censoring point?
The registry describes treatment patterns and effectiveness using data from routine clinical practice rather than a randomized assignment of treatments. The broad clinical question is therefore descriptive: what happened to eligible participants who received these first-line regimens in the database, and how long did they remain free of recorded progression or death under the endpoint definition?
Although letrozole is listed as a separate group, the available record does not establish that people in the treatment groups had comparable clinical characteristics or were followed in the same way. Differences between groups could reflect treatment selection, patient characteristics, clinical decisions, or data capture, as well as any differences associated with the regimens. The registry record does not report adjusted comparative estimates or enough group-level results to assess those possibilities.
The primary endpoint is a time-to-event measure, not a direct count of tumor shrinkage. The question concerns the time to the earliest qualifying event or censoring, analyzed using Kaplan-Meier methods. The median and its 95% confidence interval are not reported in the registry record, so the primary question cannot be answered from the posted results.
3. Trial Design
This is a completed, retrospective observational analysis sponsored by Pfizer. Its brief summary describes use of the de-identified Flatiron Health Analytic Database to characterize patient characteristics, treatment patterns, and effectiveness of palbociclib plus an aromatase inhibitor as first-line therapy in HR+/HER2- metastatic breast cancer in US clinical practices. The registry lists enrollment of 813.
The study record gives a start date of 2019-01-25 and a primary completion date of 2019-09-27. The treatment-group descriptions identify adults who initiated first-line therapy beginning Feb 3, 2015, with the end of the eligible period described relative to the data cutoff. The cutoff date itself is not reported in the registry record. The primary endpoint timeframe states that data were retrieved and observed during 9 months of the retrospective study, while the outcome could extend up to approximately 43 months. These statements describe different aspects of the record: the study observation period and the potential time represented by the endpoint.
The listed groups are palbociclib plus an aromatase inhibitor, palbociclib plus letrozole, and letrozole. The primary endpoint definition names the index date as the start of first-line palbociclib plus an aromatase inhibitor therapy. The record does not describe random assignment; it is explicitly a retrospective observational analysis. Allocation is not stated, and these groups should not be treated as a randomized, like-for-like comparison.
The eligible analysis population is described as all participants whose data were retrieved and observed in the study. The record does not report the number analyzed in each group, the criteria used to determine eligibility in detail, or how participants were distributed across the listed regimens. It also does not report a statistical analysis plan or an adjustment strategy for differences between treatment groups.
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: Data of participants was retrieved from Flatiron Health Analytic database. Available data was evaluated in 9 months of retrospective observational study.
Overall Study
| Stage | Palbociclib + AI |
|---|---|
| STARTED | 813 |
| COMPLETED | 813 |
| NOT COMPLETED | 0 |
Analysis population for the primary outcome, as defined in the registry: Analysis population included all eligible participants whose data were retrieved and observed in this 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: Analysis population included all eligible participants whose data were retrieved and observed in this study.
| Characteristic | Unit | Palbociclib + AI |
|---|---|---|
| Participants analysed | 813 | |
| Age, Continuous | Years | 64.5 (SD 11.4) |
| Sex: Female, Male: Female | Participants | 813 |
| Sex: Female, Male: Male | Participants | 0 |
| Race/Ethnicity, Customized: White | Participants | 555 |
| Race/Ethnicity, Customized: Black | Participants | 63 |
| Race/Ethnicity, Customized: Asian | Participants | 18 |
| Race/Ethnicity, Customized: Hispanic or Latino | Participants | 23 |
| Race/Ethnicity, Customized: Other/Unknown | Participants | 154 |
6. Primary Endpoint
The registry lists the primary outcome as Real-World Progression Free Survival (rwPFS): Using Kaplan-Meier Method, measured over From index date to death or disease progression or end of record/data availability or censored date, whichever occurred first, maximum up to approximately 43 months (data was retrieved and observed during 9 months of this retrospective study).
| Element | Registry entry |
|---|---|
| Result type | Median |
| Measure of spread | 95% Confidence Interval |
| Unit | Months |
| Endpoint classification | Time-to-Event Analysis |
Real-world progression-free survival is the primary endpoint. It measures time in months from the index date to death, disease progression, or the end of record or data availability, whichever occurred first. Progression is defined using the treating clinician’s conclusion based on radiology, laboratory evidence, pathology, or clinical assessment. The index date is defined as the start of first-line palbociclib plus an aromatase inhibitor therapy.
For participants without death or recorded progression, the definition specifies censoring at initiation of the next line of therapy when a participant had two or more lines of therapy, or at the last visit date when a participant had only one line. Censoring means that an event was not observed by the specified endpoint for that participant; it does not mean that the event could never occur. The analysis uses the Kaplan-Meier method, which can incorporate event times and censored observations to estimate the event-free probability over time.
The registry specifies the median and a 95% confidence interval as the endpoint summary. A median time-to-event estimate describes the point at which the estimated event-free probability reaches its midpoint. A confidence interval conveys uncertainty around an estimate; a wider interval generally indicates less precision. These are general interpretations of the statistical quantities, not findings about this study.
The median and confidence interval themselves are not reported in the registry record. The endpoint timeframe allows follow-up up to approximately 43 months, while also stating that data were retrieved and observed during 9 months of the retrospective study. The record does not give enough detail to determine the distribution of individual follow-up times.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry identifies real-world progression-free survival as the primary outcome and says it was analyzed with the Kaplan-Meier method. It does not report the median estimate or its 95% confidence interval. As a result, the central time-to-event result and its precision cannot be described from the posted results. No hazard ratio or other numerical comparative estimate is reported in the registry record.
The record lists 813 participants as enrollment, but does not report how many contributed to each treatment group or to the primary endpoint analysis. The enrollment figure therefore cannot establish the size of any individual group or the number of observed progression or death events. The registry reports zero analysis records. That absence leaves no registered numerical analysis output to use for interpreting a treatment contrast.
The study is retrospective and observational. Participants were identified according to therapies they initiated in clinical practice, rather than being assigned treatments by randomization. In general, this design can describe outcomes among people who received the recorded therapies, but differences between groups may also reflect why particular regimens were selected, differences in patient characteristics, or differences in the recording of outcomes. The registry does not report an adjustment method or comparative estimate that would address these concerns.
The endpoint combines progression and death, with censoring at specified points for people without either event. This makes the estimate dependent not only on event occurrence but also on follow-up and censoring information. In general, Kaplan-Meier interpretation relies on appropriate handling of censoring; the record gives its censoring rules but does not report diagnostics or additional details about how censoring patterns were assessed.
The registry lists secondary outcomes including overall survival, real-world tumor response, response rate, duration of treatment, time to the next line of anti-cancer therapy, and time to first chemotherapy. Numerical results for these outcomes are not reported in the registry record. The adverse-event fields list zero participants at risk or affected for serious and other events, and 176 deaths; no top serious terms are listed. These fields do not provide enough detail to interpret the adverse-event information as a complete safety analysis or to reconcile deaths with the primary endpoint.
Overall, the registry establishes the study question, observational design, endpoint definition, and intended analysis method. It does not provide the numerical outcome estimates needed to judge the observed duration of real-world progression-free survival, its precision, or any difference among the treatment groups.
9. Statistical Methods Explained
The primary endpoint uses the Kaplan-Meier method to analyze time from an index date to an event. In general, time-to-event methods are useful when participants can have different lengths of follow-up and when some participants have no recorded event by the end of their available observation. The outcome is not simply the proportion with an event: it uses both when events occur and how long participants are observed.
What does censoring mean?
Censoring occurs when the endpoint event has not been observed by a participant’s last eligible observation point. The registry defines censoring at the start of the next treatment line for participants with two or more lines, or at the last visit for those with only one line, provided they have not died or had recorded progression. A censored observation contributes information up to its censoring time, but does not establish what happened afterward. In general, interpretation depends on whether censoring is handled appropriately and whether the censoring process is informative about the event risk. The registry record does not report an assessment of that issue.
What does a Kaplan-Meier median represent?
The Kaplan-Meier method estimates the probability of remaining free of the event over time while accounting for censored observations. The median is the time at which the estimated event-free probability reaches its midpoint, if that point is reached in the observed data. It is a summary of the estimated time-to-event distribution, not an average and not a measure of tumor response. The registry names the median as the primary summary, but its value is not reported in the registry record.
How should the confidence interval be read?
A 95% confidence interval expresses uncertainty around an estimated quantity under the statistical method used. In general, an interval gives a range of values compatible with the data and method, rather than a guarantee that the true value lies in that range. Its width reflects precision: an interval can be less precise when event information is limited or follow-up is incomplete. Because neither the primary median nor its interval is reported, precision cannot be assessed for this endpoint.
What does the observational design allow?
This analysis uses existing clinical-practice data rather than randomly assigning participants to therapy. In general, observational comparisons can describe outcomes in the groups that received particular treatments, but they do not by themselves isolate treatment effects. Treatment choice may be related to patient or disease characteristics, and those characteristics may also relate to outcomes. A comparative interpretation usually requires clear group definitions, relevant covariate information, and a stated analytic approach. The registry record does not report an adjustment strategy, adjusted estimates, or a detailed statistical plan.
The registry lists three treatment groups, but the primary endpoint’s index date is defined specifically as the start of first-line palbociclib plus an aromatase inhibitor therapy. The record does not explain whether or how the endpoint definition was applied to each listed group for comparative analyses. It also does not report group-specific counts or numerical endpoint estimates. Therefore, the stated method alone is insufficient to establish a comparative treatment effect.
What is the role of the other outcomes?
The secondary outcomes cover survival, response, treatment duration, and subsequent treatment timing. These outcomes represent different aspects of care and would require their own operational definitions and analyses. The registry names Kaplan-Meier methods for overall survival, duration of treatment, time to next line of anti-cancer therapy, and time to first chemotherapy. It also lists real-world tumor response and response rate. Numerical results for these outcomes are not reported in the registry record, and the record does not describe the analysis details for every outcome.
In general, examining multiple outcomes creates a multiplicity question: when many outcomes are tested or interpreted, the chance of finding an apparently notable result by chance can increase. Whether and how to address this depends on the aims and analysis plan. A multiplicity plan is not reported in the registry record, so it is not possible to determine whether any adjustment or prioritization was planned. No efficacy conclusion should be inferred from the list of outcomes alone.
The record also describes planning sample-size illustrations based on an observed effect, equal allocation, a two-sided significance level of 0.05, and a normal approximation. Such calculations are planning illustrations, not observed power and not evidence that a treatment effect exists. The numerical planning values and an observed effect estimate are not reported in the registry record. The record does not report a sample-size justification for this retrospective analysis.
10. Multiplicity, Missing Data and Analysis Populations
The registry lists the primary real-world progression-free survival outcome and a set of secondary outcomes covering overall survival, response, treatment duration, and subsequent treatment timing. It does not report a multiplicity strategy, such as an ordering of hypotheses or an adjustment for examining multiple outcomes. In general, multiplicity matters because interpreting many statistical comparisons can increase the chance of a seemingly notable result arising by chance. Without a reported plan and numerical results, the implications for this study cannot be assessed.
Missing-data procedures are not reported in the registry record. The endpoint definition does specify censoring for participants without recorded progression or death: at the next-line treatment date for participants with two or more treatment lines, or at the last visit date for participants with only one line. These rules describe endpoint censoring, but do not explain how missing covariates, incomplete records, or absent outcome information were handled.
The stated analysis population includes all eligible participants whose data were retrieved and observed in the study. The record does not report the detailed eligibility criteria, group-specific analysis counts, exclusions from the enrolled population, or how missing records affected inclusion. Enrollment is listed as 813, but this does not establish the number included in any particular endpoint analysis.
The registry also does not report whether outcomes were assessed uniformly across treatment groups, whether follow-up differed by group, or whether sensitivity analyses were conducted. These omissions matter in a retrospective database analysis because endpoint availability and clinical documentation can vary. No conclusion about the direction or size of any resulting bias can be drawn from the record.
11. What the Result Does, and Does Not, Mean
The registry record describes an analysis of treatment patterns and outcomes among people receiving first-line therapy in clinical practice. Its primary endpoint is a defined time-to-event measure, and the Kaplan-Meier method is specified. Those details explain what the analysis was intended to measure, but they do not establish an outcome value.
The median real-world progression-free survival and its 95% confidence interval are not reported in the registry record. Numerical results for the listed secondary outcomes are also not reported. Consequently, the posted results do not allow a reader to assess the typical observed time to progression or death, the precision of that estimate, or how outcomes differed across the treatment groups.
The design also limits what a comparison could mean. This was a retrospective observational study, not a randomized comparison, and allocation is not stated. People receiving different treatments may differ in ways related to their outcomes. Without reported group-specific results, adjustment methods, and appropriate contextual information, an observed contrast could not be interpreted as an effect caused by treatment.
More generally, real-world data can describe care and outcomes in the settings represented by a database, while relying on recorded clinical information and the definitions used to identify events. The endpoint includes clinician-assessed progression and uses data availability and treatment changes to define follow-up. Those features are relevant when interpreting the outcome, but the registry does not report details that would quantify their impact.
The record therefore supports a description of the study design and endpoint, not a conclusion that one regimen was more or less effective. It also does not support a clinical recommendation. The absence of reported estimates is not evidence of no effect; it means the effect and its precision cannot be evaluated from the registry record.
12. Why This Trial Matters Statistically
This study is statistically notable as a retrospective analysis of treatment patterns and effectiveness in clinical practice, using a de-identified database rather than prospective random assignment. Such analyses can address questions about routine care, but they require careful attention to how participants enter treatment groups, how outcomes are documented, and how follow-up ends.
The primary endpoint brings together progression, death, and specified censoring events. This makes the endpoint definition central to interpretation: the recorded time reflects a combination of clinical assessment, database availability, and treatment history. The registry gives a detailed description of the endpoint and its censoring rules, which helps identify the intended estimand, but does not report enough results or analytic detail to evaluate the estimate itself.
The distinction between observation time and potential follow-up is also important. The record states that data were retrieved and observed during 9 months of the retrospective study and that endpoint follow-up could extend up to approximately 43 months. These are not interchangeable quantities. In general, a reader needs to know how much follow-up was available for participants and how many events occurred to understand the precision of a time-to-event estimate. Those details are not reported in the registry record.
Finally, the record illustrates why outcome definitions and statistical methods do not replace numerical results. A median, confidence interval, and adequately described comparison would be needed to judge the observed pattern and its uncertainty. Because the primary estimate and comparative analyses are not reported, the record is informative about the intended question and design but cannot support a quantitative effectiveness conclusion.
13. 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 registry record has substantial limits for statistical interpretation. It does not report the primary median or its 95% confidence interval, group-specific endpoint results, or numerical estimates for secondary outcomes. It lists enrollment of 813 but does not give treatment-group counts or the number included in each endpoint analysis. The registry also reports zero analysis records, leaving no registered numerical analysis output to interpret.
The study is retrospective and observational, and allocation is not stated. The listed treatment groups therefore do not constitute a randomized, like-for-like comparison. The record does not report baseline characteristics by group, a method for adjusting for differences between groups, or an adjusted comparative estimate. The extent and direction of any confounding cannot be determined.
Important implementation details are not reported in the registry record, including the data cutoff date, detailed eligibility criteria, missing-data procedures, assessment of censoring, and a statistical analysis plan. Although the endpoint definition identifies clinician-assessed progression and specifies censoring rules, the record does not describe how progression was validated or how differences in documentation and follow-up were assessed.
The record lists secondary outcomes and planning sample-size assumptions, but it does not report numerical results for those outcomes or the numerical planning illustrations. A sample-size illustration based on an observed effect is not evidence of observed power. The absence of a reported multiplicity plan also limits interpretation across the several outcomes. Adverse-event fields list zero participants at risk or affected for serious and other events, along with 176 deaths, but the registry does not provide enough detail to interpret these fields as a complete safety analysis.
14. Related Tutorials
15. Related Statistical Calculators
16. Sources
- ClinicalTrials.gov: Real-world Treatment Patterns and Effectiveness of Palbociclib and AI Therapy — NCT04176354.
- Registry record last updated 2024-08-23; status last verified 2024-08.
- Results first posted 2024-08-23.
- 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.
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17. Record Summary
NCT04176354 is a completed, retrospective observational analysis sponsored by Pfizer, with enrollment listed as 813. The study used the de-identified Flatiron Health Analytic Database to describe characteristics, treatment patterns, and effectiveness for first-line palbociclib plus an aromatase inhibitor in HR+/HER2- metastatic breast cancer in US clinical practices.
The record lists palbociclib plus an aromatase inhibitor, palbociclib plus letrozole, and letrozole as treatment groups. Real-world progression-free survival is the primary endpoint, analyzed by Kaplan-Meier methods and summarized by a median with a 95% confidence interval. The median and interval are not reported in the registry record. Numerical results for the secondary outcomes are also not reported, and the record contains zero analysis records.
The study began on 2019-01-25 and reached primary completion on 2019-09-27. As an observational analysis without a randomized, like-for-like control comparison, its design and missing numerical results do not support a causal treatment conclusion.