Treatment Patterns And Clinical Outcomes Among Patients in Latin America Receiving First Line Palbociclib Combinations For HR+/HER2- Advanced/Metastatic Breast Cancer In Real World Settings.: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Treatment Patterns And Clinical Outcomes Among Patients in Latin America Receiving First Line Palbociclib Combinations For HR+/HER2- Advanced/Metastatic Breast Cancer In Real World Settings. (NCT05155566), a registered phase not stated study. The primary outcome is Progression Free Rate at Month 6.

2. Clinical Question

The study aim was descriptive: to characterize patient demographics, clinical features, treatment patterns, and clinical outcomes in real-world care across Latin America. It was not registered as a randomized comparison of palbociclib combinations. Consequently, the central question supported by the stated design is about the observed course of the enrolled population, rather than whether one combination caused a better outcome than another.

The record identifies breast cancer as the condition and describes the population as adult female patients with hormone receptor-positive, HER2-negative advanced or metastatic disease. It does not report country-level enrollment, detailed eligibility criteria, or the number of participants meeting each clinical characteristic. Those details are not reported in the registry record.

The primary endpoint is a time-to-event-derived rate, estimated by Kaplan-Meier analysis. Although the registry defines the endpoint and its time point, it does not include an estimate, confidence interval, or other inferential result. The available record therefore establishes what the study intended to describe, but not the observed value of that endpoint.

3. Trial Design

NCT05155566 is a completed, real-world observational study sponsored by Pfizer. The registry lists enrollment of 847. The study began on 2019-05-15, and primary completion is listed as 2021-03-12. The registry describes retrospective collection and observation over approximately 22 months for the primary endpoint.

The study aimed to describe demographics, clinical characteristics, treatment patterns, and outcomes among adult female patients in Latin America who received palbociclib combinations as first-line therapy for HR+/HER2- advanced or metastatic breast cancer. Treatment was described regardless of combination partner and labelled use. This is a descriptive aim, not an experimental assignment of treatment.

The record lists palbociclib plus an aromatase inhibitor and palbociclib plus fulvestrant in its treatment-group information. It does not state how treatment was selected or allocated, or whether the listed groups were intended as a formal comparison. The allocation method is not reported in the registry record. As the record itself cautions, these groups are not a like-for-like control comparison.

The primary endpoint was progression-free rate at month 6, estimated using Kaplan-Meier analysis. The outcome population is described as the full analysis set, comprising participants for whom a complete medical record review was conducted; the overall number analyzed means participants evaluable for this particular outcome. That evaluable count is not reported in the registry record.

The record lists 24 outcome measures and zero analyses. It does not provide primary endpoint results or statistical comparisons. A protocol-level statistical plan, sample-size justification, interim analysis plan, and details of covariate adjustment are not reported in the registry record. Planning assumptions described for sample-size illustrations should not be mistaken for the design of this observational study or for evidence about its precision.

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

Analysis population for the primary outcome, as defined in the registry: FAS comprised of participants for whom a complete medical record review was conducted. Here, "overall number of participants analyzed" signifies participants evaluable for this outcome measure.

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: Full Analysis Set (FAS) comprised of participants for whom a complete medical record review was conducted.

6. Primary Endpoint

The registry lists the primary outcome as Progression Free Rate at Month 6, measured over Month 6 (from the data collected and observed retrospectively for approximately 22 months).

The primary endpoint is progression-free rate at month 6, expressed as a percentage of participants and estimated by Kaplan-Meier analysis. The definition starts at initiation of palbociclib combination treatment. A progression event could be clinician-documented disease progression while the participant was receiving palbociclib, death, or starting a new therapy line after the final palbociclib dose when progression was the reason for stopping palbociclib. Participants without one of those events were censored at their last available follow-up.

The registry defines disease progression as an increase of at least 20% in the sum of target-lesion diameters relative to the smallest sum on study, with an absolute increase of at least 5 mm, or the appearance of one or more new lesions. The endpoint therefore combines clinical records and specified disease-assessment criteria rather than treating all treatment discontinuations as progression.

As a general statistical concept, a time-to-event rate can use information from participants whose follow-up ends before the endpoint time, provided their event status up to censoring is known. Kaplan-Meier estimation accounts for differing follow-up durations rather than simply dividing a count by a group size. It is used for this endpoint because participants may have different observation times. The month 6 estimate and its uncertainty are not reported in the registry record, so the endpoint definition can be described but its observed magnitude cannot be interpreted.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does the Kaplan-Meier estimate represent?

The registry says that progression-free rate was estimated using Kaplan-Meier analysis. As a general statistical explanation, Kaplan-Meier methods estimate the probability of remaining free of an event over time while allowing participants to have different lengths of observation. A participant who has not had a defined event by their last contact can contribute information up to that point and then be censored. This differs from a simple proportion that counts only events and divides by a fixed denominator, because follow-up may end at different times.

For this study, the defined events included clinician-documented progression on palbociclib, death, and a new therapy line after stopping palbociclib when progression was the reason for discontinuation. Participants without those events were censored at last available follow-up. As a general consideration, Kaplan-Meier interpretation depends on censoring not systematically selecting participants with different future event risks, after accounting for the analysis design. Whether that assumption was examined is not reported in the registry record.

How is progression defined?

The record combines a clinical documentation criterion with a lesion-based definition. It describes progression as an increase of at least 20% in the sum of target-lesion diameters compared with the smallest sum observed on study, together with an absolute increase of at least 5 mm, or the appearance of one or more new lesions. It also includes clinician-documented disease progression while on palbociclib in the event definition. These rules make the endpoint more specific than a general label such as worsening disease, but the record does not report how progression assessments were collected or reviewed.

Endpoint rules are important because changing the event definition can change which observations count as events and when. The stated definition also distinguishes a therapy change associated with progression from a therapy change for another reason. The registry does not give further detail on adjudication, consistency of records across sites, or how ambiguous documentation was handled; those details are not reported in the registry record.

What information is needed to interpret an estimate?

A point estimate would describe the estimated progression-free rate at month 6. A confidence interval, as a general statistical concept, would convey the range of values reasonably compatible with the observed data under the method's assumptions. Neither the endpoint estimate nor a confidence interval is reported in the registry record. The number evaluable, event count for this endpoint, and details such as numbers censored are also not reported. Without these quantities, readers cannot assess the result's precision or inspect how the observed data contributed to the estimate.

The registry defines the analysis population as participants with a complete medical record review and uses evaluable participants for the overall number analyzed. This is an outcome-specific concept: enrollment is not necessarily the same as the number included in the analysis. The record gives enrollment of 847, but does not state how many participants were evaluable for the month 6 endpoint. It also does not report whether any participants were excluded from that analysis or why.

Why is this not a randomized treatment comparison?

The study is described as real-world and retrospective, and allocation is not stated. In a randomized trial, allocation by chance is intended to balance measured and unmeasured baseline characteristics across groups on average. That protection cannot be assumed for treatment categories in an observational study. As a general statistical concern, clinical factors may influence treatment selection and also relate to outcomes, creating confounding in an unadjusted comparison.

The registry lists palbociclib plus an aromatase inhibitor and palbociclib plus fulvestrant, but does not establish that these categories are comparable in patient characteristics, follow-up, or other care. It does not report adjusted effects or a model for comparing them. Thus, even if group-specific outcome estimates were available, they would describe associations unless the analysis and assumptions supported a stronger interpretation. No such comparative analysis is reported in the registry record.

What do the planning assumptions mean?

The registry describes planning illustrations based on the observed effect, with a two-sided significance level of 0.05, equal allocation, and a normal approximation. It says the effect to detect is a stated fraction of the observed effect. For time-to-event illustrations, the stated quantity is total events using the Schoenfeld method; for other outcomes, it is participants per arm. These are planning calculations, not observed trial outcomes, and the record does not report the resulting illustration values or the fractions used.

Such illustrations do not establish the study's original design, because this is a retrospective observational study and its own sample-size justification is not reported in the registry record. Nor do planning values constitute observed power. General statistical practice treats uncertainty in the observed effect as central to interpreting a study; a planning calculation based on an observed effect cannot replace the actual endpoint estimate, its uncertainty, and a clear account of the analysis population.

10. Exact Estimates for Each Arm

No two-arm comparison is shown for this trial, but each arm's result can still be summarized with exact interval estimates computed from the posted counts. The Clopper-Pearson interval is exact and conservative; the Wilson interval is a common closer-to-nominal alternative; the Bayesian credible interval uses a uniform Beta(1, 1) prior. For small groups the three can differ noticeably.

R code and output

arm    <- c("Palbociclib + Aromatase Inhibitor", "Palbociclib + Fulvestrant")
n      <- c(573, 273)
events <- c(535, 249)
for (i in seq_along(n)) {
  ci <- binom.test(events[i], n[i])$conf.int          # Clopper-Pearson exact interval
  cr <- qbeta(c(0.025, 0.975), 1 + events[i], 1 + n[i] - events[i])   # Bayesian, uniform Beta(1,1) prior
  wi <- (function(x, n) { p <- x / n; z <- qnorm(0.975); d <- 1 + z^2 / n
    c((p + z^2 / (2 * n) - z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d, (p + z^2 / (2 * n) + z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d) })(events[i], n[i])
  cat(sprintf("ARM|%s|%d|%d|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f\n", arm[i], n[i], events[i], 100 * events[i] / n[i],
              100 * ci[1], 100 * ci[2], 100 * wi[1], 100 * wi[2], 100 * cr[1], 100 * cr[2]))
}

ARM  Palbociclib + Aromatase Inhibitor  573  535  93.4  91.0  95.3  91.0  95.1  91.0  95.1
ARM  Palbociclib + Fulvestrant  273  249  91.2  87.2  94.3  87.3  94.0  87.2  94.0

11. Multiplicity, Missing Data and Analysis Populations

The registry lists 24 outcome measures but zero analyses. It identifies progression-free rate at month 6 as the primary endpoint, yet does not report an estimate, confidence interval, or test result. No adjustment for multiple outcomes or multiple testing is reported in the registry record. Without analysis results, it is not possible to determine how the outcomes were handled statistically or whether any multiplicity procedure was used.

The endpoint population is defined as participants for whom a complete medical record review was conducted, with the overall number analyzed referring to participants evaluable for that outcome. The evaluable count is not reported. The record does not describe the extent or pattern of missing clinical records, missing endpoint information, or any imputation procedure. These missing-data methods are not reported in the registry record.

Censoring is part of the specified time-to-event endpoint: participants without a defined event were censored at their last available follow-up. This is distinct from a complete accounting of missing data. The record does not give the amount of censoring, follow-up distribution, or an assessment of whether censoring could be related to prognosis. Those details are not reported in the registry record.

The record gives an enrollment figure of 847, but it does not provide a flow from enrollment to endpoint evaluation, reasons for non-evaluation, or analysis populations for the other outcomes. It therefore cannot establish whether outcome availability differed across treatment categories. No interim analyses or prespecified statistical analysis plan are reported in the registry record.

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

The record establishes that a retrospective real-world study set out to describe treatment patterns and clinical outcomes for first-line palbociclib combinations in Latin America. It defines progression-free rate at month 6 and specifies a Kaplan-Meier approach. These features clarify what outcome was intended and how it was to be interpreted.

However, the primary endpoint estimate and its uncertainty are not reported in the registry record. The record therefore does not show the level of progression-free status observed at month 6 or how precise that estimate was. A definition alone cannot answer whether the observed rate was high or low, nor can it establish a treatment effect.

The listed treatment categories are not randomized comparison groups, and their allocation method is not stated. They should not be read as a controlled comparison. Differences in patient characteristics, treatment selection, documentation, and follow-up could affect observed outcomes. The registry does not report comparative adjusted estimates that might address these issues.

The death counts listed for the treatment categories are 54 and 15, respectively, but denominators and timing are not reported. Counts alone cannot be interpreted as group-specific risks or used to compare mortality. The registry's serious and other adverse-event fields are recorded as zero for the listed groups; the record provides no denominators or additional context, and it does not list serious-event terms. These entries do not establish the absence of adverse events.

Thus, the posted record is useful for understanding the study's descriptive scope and endpoint definitions, but it does not provide outcome results sufficient to evaluate the primary endpoint, compare regimens, or make causal claims. Missing estimates and analysis details are not evidence for any particular direction or magnitude of outcome.

13. Why This Trial Matters Statistically

Real-world studies can describe how treatments are used and what outcomes are recorded in clinical practice, providing context that differs from a randomized trial. This study's stated focus is patients in Latin America receiving first-line palbociclib combinations for HR+/HER2- advanced or metastatic breast cancer. Its descriptive aim includes treatment patterns as well as clinical outcomes, a scope that may be relevant to understanding care across the region.

Statistically, the record highlights why an endpoint definition and an endpoint result are both necessary. It specifies progression-free status, event rules, censoring, and Kaplan-Meier estimation, but does not report the resulting month 6 rate or uncertainty. Readers can understand the intended estimand, but cannot judge its magnitude or precision from the registry record.

The record also illustrates the difference between observational treatment groups and randomized arms. Treatment categories can be described, but the allocation method is not stated and the groups are explicitly not a like-for-like control comparison. This distinction matters because an observed contrast in routine-care data does not by itself identify a treatment effect. Patient selection and other differences may influence both treatment and outcome.

Finally, enrollment is not necessarily the same as the population analyzed for a specific endpoint. The registry defines an evaluable population based on complete medical record review but does not report its size. That gap limits assessment of follow-up completeness and the population represented by the endpoint. The statistical value of the record is therefore strongest in documenting the question and definitions, while its outcome and comparative conclusions remain unavailable.

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 most consequential limitation for interpretation is that the month 6 progression-free estimate is not reported in the registry record. The number evaluable, endpoint event count, confidence interval, and details of censoring are also not reported. Without those details, neither the observed outcome nor its precision can be assessed.

The study is retrospective and observational. Allocation is not stated, and the registry cautions that the listed treatment groups are not a like-for-like control comparison. The record does not report adjusted comparative analyses or details that would establish balance in clinical characteristics. Consequently, the listed categories cannot support a causal comparison from the information recorded.

The population is described broadly as adult female patients in Latin America with HR+/HER2- advanced or metastatic breast cancer receiving first-line palbociclib combinations. Country-level results, detailed eligibility criteria, and distributions of clinical characteristics are not reported in the registry record. The completeness and consistency of the underlying medical records are also not described beyond defining the analysis population by complete medical record review.

The reported observation timeframe is approximately 22 months, but the record does not provide the follow-up distribution for participants or how many were censored before the endpoint time. It does not describe missing-data procedures, handling of incomplete records, or endpoint adjudication. Those methodological details are not reported in the registry record.

Although the record lists deaths by treatment category, it does not provide group denominators, timing, causes, or a comparative mortality analysis. Serious and other adverse-event fields are recorded as zero for the listed groups, without additional context or listed serious-event terms. These entries cannot substitute for a complete adverse-event account. The registry lists 24 outcomes but zero analyses, and does not report a statistical analysis plan or multiplicity approach.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Treatment Patterns And Clinical Outcomes Among Patients in Latin America Receiving First Line Palbociclib Combinations For HR+/HER2- Advanced/Metastatic Breast Cancer In Real World Settings. — NCT05155566.
• Registry record last updated 2024-01-26; status last verified 2023-05.
• Results first posted 2024-01-26.
• 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

NCT05155566 is a completed, Pfizer-sponsored, retrospective real-world study of first-line palbociclib combinations among adult female patients in Latin America with HR+/HER2- advanced or metastatic breast cancer. The registry lists enrollment of 847, a start date of 2019-05-15, and primary completion on 2021-03-12. The stated observation period for the primary outcome is approximately 22 months.

The primary endpoint is progression-free rate at month 6, estimated by Kaplan-Meier analysis. The record defines progression and censoring but does not report the endpoint estimate, its uncertainty, or the evaluable count. It lists 24 outcome measures and zero analyses.

Palbociclib plus an aromatase inhibitor and palbociclib plus fulvestrant appear in the treatment-group information. The record lists 54 deaths and 15 deaths for those groups, respectively, without denominators or timing. The treatment categories are not a like-for-like control comparison, and allocation is not stated.