Study of Efficacy of Ribociclib After Progression on CDK4/6 Inhibition in Patients With HR+ HER2- Advanced Breast Cancer: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Study of Efficacy of Ribociclib After Progression on CDK4/6 Inhibition in Patients With HR+ HER2- Advanced Breast Cancer (NCT02632045), a randomized phase 2 study. The primary outcome is Progression Free Survival (PFS).

2. Clinical Question

The clinical question concerns whether continuing CDK4/6 inhibition with a change in anti-estrogen therapy is associated with a different progression-free survival pattern than changing anti-estrogen therapy while using placebo. The trial record describes a randomized phase II comparison with double masking and parallel groups. The primary result is reported as a median for each group, with a 95% confidence interval for each median.

The population definition is important to the scope of the question. This was not a comparison in all patients with breast cancer, nor a comparison of ribociclib against fulvestrant as separate treatments. Both groups received fulvestrant; the assigned oral treatment differed. The record describes prior progression on an aromatase inhibitor plus a CDK4/6 inhibitor and identifies palbociclib or ribociclib as possible prior inhibitors. It does not report separate results by which inhibitor patients had previously received.

The primary endpoint was progression-free survival, defined from randomization until objective disease progression by local assessment or death from any cause. Overall response rate and clinical benefit rate were also posted as secondary outcomes. Those endpoints provide additional outcome perspectives, but they do not replace the primary time-to-event question.

3. Trial Design

MAINTAIN was a randomized phase II trial with double masking and a parallel-group design. The registry record lists enrollment of 169. The two assigned regimens were ribociclib with fulvestrant and placebo with fulvestrant. The placebo schedule matched the ribociclib schedule, and both groups received the same fulvestrant schedule. This design frames the contrast around adding ribociclib to fulvestrant rather than around differing fulvestrant regimens.

The record describes the eligible disease as unresectable or metastatic hormone receptor-positive, HER2-negative breast cancer after progression on anti-estrogen therapy plus CDK4/6 inhibition. The brief summary specifies an aromatase inhibitor as the prior anti-estrogen therapy and names palbociclib or ribociclib as prior CDK4/6 inhibitors. The record does not report outcomes split by prior inhibitor or other patient subgroups.

The primary endpoint was progression-free survival, with a stated timeframe of up to approximately 30 months. The registry reports median progression-free survival of 2.76 months for placebo/fulvestrant, with a 95% confidence interval of 2.66 to 3.25, and 5.29 months for ribociclib/fulvestrant, with a 95% confidence interval of 3.02 to 8.12. The posted group counts for this endpoint are 59 and 60, respectively. These counts describe the endpoint record and should not be treated as a complete account of the analysis population; that population is not reported in the registry record.

The registry also lists overall response rate and clinical benefit rate as secondary outcomes. Their recorded timeframes differ: overall response rate was measured every 12 weeks up to 6 months, and clinical benefit rate was assessed up to 24 weeks. The record does not describe the statistical plan, sample-size justification for the trial itself, analysis populations, or interim analyses. The registry lists the trial as completed and gives primary completion as 2022-01-04.

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: A total of 169 participants signed a consent form. Of those, 47 were not randomized or did not start due to the following: n=21 were screen failures, n=18 withdrew consent prior to randomization, n=4 were not randomized due to non-progression. n=4 were randomized however withdrew consent prior to treatment initiation and did not start.

Overall Study

Reasons for not completing this period:

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 Progression Free Survival (PFS), measured over Up to approximately 30 months.

Progression-free survival measures the time from randomization until objective disease progression or death from any cause. The registry specifies that progression was assessed locally using radiographic studies every three treatment cycles, approximately every 12 weeks (+/- 1 week). Progression was defined by RECIST 1.1, including at least a 20% increase in the sum of target-lesion diameters from the smallest sum recorded on study, together with an absolute increase of at least 5 mm. The appearance of new lesions also counted as progression.

This endpoint is used to describe how long participants remain alive without recorded progression. It incorporates both progression and death, rather than describing tumor response alone. The posted result is the median time in each assigned group. A median is the point in the observed time distribution at which half of the relevant observations fall on either side, subject to the time-to-event estimation and censoring methods used. General explanation: a confidence interval communicates uncertainty around an estimated quantity; a wider interval indicates less precision than a narrower interval, all else equal.

The registry reports the endpoint timeframe as up to approximately 30 months. It does not report the number of progression or death events, a hazard ratio, or a sponsor-reported statistical test comparing the groups. The two group medians therefore describe the posted results but do not, on their own, provide a complete comparative time-to-event analysis.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry reports a median time-to-event endpoint and confidence intervals for each assigned group. It does not report the sponsor's comparative hazard ratio or a statistical test for progression-free survival. The distinction matters: a pair of group-specific medians is descriptive, while a hazard ratio summarizes a relative event rate over the observed follow-up under the assumptions of the chosen time-to-event model. Without a sponsor-reported comparative estimate, the primary result should not be recast as a relative effect.

What does a median time-to-event estimate describe?

General explanation: time-to-event data measure how long it takes until a defined event occurs. Participants who have not experienced the event by the end of their available follow-up may be censored, meaning their time is known up to that point but the eventual event time is not observed. Methods for estimating a median can incorporate censored observations. The registry record does not state the estimator, censoring rules, or analysis details used for the posted medians.

The endpoint definition includes progression and death from any cause. Its event timing also depends on radiographic assessment: the record specifies assessment every three treatment cycles, approximately every 12 weeks (+/- 1 week), and identifies local assessment under RECIST 1.1. Thus the measured progression time is informed by scheduled assessments rather than continuous observation. The record does not provide additional details about assessment adherence or independent review.

What does a confidence interval contribute?

General explanation: a confidence interval conveys the precision of an estimate under the statistical method used to construct it. It is not a range containing every participant's outcome, and it does not by itself answer whether two groups differ. The intervals around the reported medians are 2.66 to 3.25 months for placebo/fulvestrant and 3.02 to 8.12 months for ribociclib/fulvestrant. Their widths convey that the latter median is less precisely estimated in the posted record. A direct comparative inference would ordinarily rely on a specified between-group method, but that result is not reported for the primary endpoint.

How should the secondary comparisons be read?

The registry posts overall response rate and clinical benefit rate as binary outcomes, with counts by group and recalculated unadjusted comparisons. A risk difference expresses a difference between two event proportions; a confidence interval represents uncertainty in that difference. General explanation: an unadjusted p-value evaluates a comparison without accounting for a wider family of tests. It does not convey the size or precision of an effect, and a small p-value does not correct for multiple outcome testing. The registry lists no sponsor-reported analyses for these secondary endpoints, so the recalculations should not be mistaken for the sponsor's own inferential results.

The posted comparison estimates and planning illustrations for secondary outcomes are based on summary statistics. The record states that planning illustrations assume a two-sided significance level of 0.05, equal allocation, and a normal approximation, with the effect to detect set at the stated fraction of the observed effect. For overall response rate, the illustration gives 282 participants per arm for 80% power when planning for 100% of the observed effect, and 474 participants per arm for 80% power when planning for 75% of the observed effect. For clinical benefit rate, the corresponding figures are 110 participants per arm and 189 participants per arm. These are planning illustrations based on observed effects, not observed power and not the trial's own design justification. The trial's sample-size assumptions are not reported in the registry record.

General explanation: observed-effect planning can be unstable because an effect estimated in a study may be imprecise. Planning for a smaller effect generally requires more participants than planning for a larger effect, all else equal. These illustrations should therefore be interpreted as conditional planning scenarios, not as evidence that the trial had a particular probability of detecting its observed result. They do not explain the actual enrollment decision for MAINTAIN.

What can be inferred from the posted analyses?

The registry lists zero reported analyses for the trial outcomes. For the secondary outcomes, the displayed unadjusted calculations are simple recalculations from the posted group summaries. They are not presented as adjusted analyses, and no multiplicity strategy is reported. For the primary outcome, the registry supplies medians and confidence intervals but not the sponsor's comparative hazard ratio. The record also does not state whether any adjusted models, sensitivity analyses, or subgroup analyses were conducted. Those missing details limit the statistical conclusions that can be drawn from the registry results.

10. Multiplicity, Missing Data and Analysis Populations

The registry record does not report a statistical analysis plan, a multiplicity strategy, or whether the primary endpoint was tested under a prespecified hierarchy. It lists overall response rate and clinical benefit rate as secondary outcomes, but does not state whether they were confirmatory, exploratory, or subject to adjustment for multiple testing. Their unadjusted recalculated comparisons should not be interpreted as if they controlled the chance of false-positive findings across outcomes.

Missing-data methods are not reported in the registry record. It does not describe how participants without an observed endpoint, incomplete assessments, withdrawals, or loss to follow-up were handled. For progression-free survival, the record does not report censoring rules, event counts, or the estimator used for the medians. These omissions prevent a full assessment of how incomplete follow-up may affect the reported time-to-event results.

Analysis populations are also not reported in the registry record. The listed enrollment is 169, while the primary endpoint groups have recorded counts of 59 and 60, and the overall response rate has recorded denominators of 35 in each group. The record does not explain these differences or identify whether the counts represent randomized participants, participants assessed for an endpoint, or another analysis set. No population should be inferred from those counts alone.

The registry lists zero reported analyses. It does not report interim analyses, subgroup analyses, sensitivity analyses, or an adjustment strategy for baseline factors. These are absences of documentation in the registry record; they do not establish what was or was not done outside the posted information. Consequently, the statistical evidence should be described as the posted medians and unadjusted secondary recalculations, without attributing unreported methods to the trial.

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 5% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: lung infection (3.3%), skin infection (1.7%), kidney infection (1.7%).

The registry records serious adverse events in 0 of 59 participants in the placebo/fulvestrant group and 4 of 60 in the ribociclib/fulvestrant group. These counts describe the serious-event figures recorded for the two groups. They do not, by themselves, characterize the full range, timing, duration, or severity of all adverse effects, and the registry record does not provide a comparative statistical analysis of these counts.

The most frequently listed serious adverse event terms are Lung Infection at 3.3%, Skin Infection at 1.7%, and Kidney Infection at 1.7%. The record does not provide additional event-level details in the posted summary. It also records 2 deaths in each group; the record does not establish from these figures whether deaths were attributed to treatment, disease, or another cause.

General explanation: safety counts are best interpreted with their group denominators and the definitions and observation period used for collection. These details do not establish whether an event was caused by a treatment. The registry summary does not report a full comparative safety analysis, exposure-adjusted rates, or a detailed account of attribution. The figures should therefore be read as descriptive registry counts, not as a complete safety comparison.

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

The registry results show a longer posted median progression-free survival in the ribociclib/fulvestrant group than in the placebo/fulvestrant group. The group medians are 5.29 months and 2.76 months, respectively, with confidence intervals of 3.02 to 8.12 months and 2.66 to 3.25 months. These estimates describe the observed record; they are not a direct estimate of how much an individual participant's outcome would change.

The posted result does not establish a definitive comparative treatment effect. The registry does not report a primary hazard ratio, confidence interval for a comparative effect, or sponsor-reported test. Confidence intervals for separate medians do not substitute for those statistics. The secondary outcome calculations are unadjusted and do not resolve the missing primary comparative analysis or the unreported multiplicity approach.

The result also applies to the population described in the registry: patients with unresectable or metastatic HR-positive, HER2-negative breast cancer after progression on anti-estrogen therapy plus CDK4/6 inhibition. The record does not provide subgroup results by prior CDK4/6 inhibitor, nor does it establish how the observed pattern applies to populations outside that description.

General explanation: randomized comparisons can support causal interpretation when the design, follow-up, outcome measurement, and analysis are appropriately implemented. However, the registry record alone does not document enough analysis detail to assess all those conditions. The numerical summaries should be read with their uncertainty and reporting limits in view. They do not support a claim about what an individual should receive, and they do not show that either regimen works or does not work.

13. Why This Trial Matters Statistically

This trial is statistically interesting because it addresses treatment sequencing after progression on prior CDK4/6 inhibition. The randomized comparison keeps fulvestrant common to both groups and varies the accompanying oral assignment between ribociclib and placebo. That arrangement makes the clinical contrast more focused than a comparison in which both the anti-estrogen treatment and the CDK4/6 inhibitor differed at once.

The primary endpoint is time-to-event, but the registry posts group medians rather than the comparative hazard ratio usually used to summarize a time-to-event contrast. This distinction illustrates why descriptive summaries and inferential comparisons answer different questions. The medians show the central timing estimates, while the missing comparative statistic limits assessment of the relative pattern over follow-up and its precision.

The record also illustrates the limits of interpreting secondary endpoints in isolation. Overall response rate and clinical benefit rate point numerically in the same direction as the primary medians, but their unadjusted recalculations, separate timeframes, and unreported multiplicity approach make them less decisive. Planning illustrations derived from observed secondary effects can inform hypothetical future planning, but they are not evidence of observed power and do not explain the trial's actual enrollment design.

Finally, the registry record separates what is posted from what remains unknown. The outcome summaries are available, while analysis populations, missing-data handling, primary comparative inference, and the trial's own sample-size rationale are not reported. Recognizing that boundary is central to sound interpretation: the observed pattern can be described without overstating the strength or completeness of the statistical evidence.

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.

A trial-specific limitation in the registry record is the absence of a comparative hazard ratio for progression-free survival. The primary outcome is presented through group medians and confidence intervals, which do not provide the same comparative information as a hazard ratio and its uncertainty. The record also does not identify the time-to-event estimation procedure, censoring rules, or event counts.

The record gives different endpoint counts: 59 and 60 for progression-free survival, and 35 in each group for overall response rate. It does not explain these denominators or identify the analysis populations. Enrollment is listed as 169, but the registry does not reconcile enrollment with the endpoint counts. Missing-data handling and reasons for unavailable outcome records are not reported.

There is also limited detail on outcome assessment. Progression was based on local assessment, with radiographic review every three treatment cycles, approximately every 12 weeks (+/- 1 week). The record does not report independent review, assessment adherence, or sensitivity analyses addressing assessment timing. The primary timeframe is up to approximately 30 months, but the record does not provide a more detailed description of follow-up.

The registry does not report subgroup results, the trial's own sample-size justification, multiplicity procedures, interim analyses, or the statistical analysis plan. The secondary comparison estimates are unadjusted recalculations, and the record lists no reported analyses. These limitations do not demonstrate that particular methods were absent from the conduct of the trial; they indicate that the relevant details are not reported in the registry record.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Study of Efficacy of Ribociclib After Progression on CDK4/6 Inhibition in Patients With HR+ HER2- Advanced Breast Cancer — NCT02632045.
• Registry record last updated 2024-12-06; status last verified 2024-12.
• Results first posted 2024-12-06.
• 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

MAINTAIN was a randomized, double-masked, parallel phase II trial in patients with unresectable or metastatic HR-positive, HER2-negative breast cancer after progression on anti-estrogen therapy plus CDK4/6 inhibition. It compared fulvestrant with ribociclib against fulvestrant with placebo. Enrollment is listed as 169, and the trial status is completed.

The primary endpoint was progression-free survival, defined from randomization to objective progression by local assessment or death from any cause. The registry reports medians of 2.76 months for placebo/fulvestrant and 5.29 months for ribociclib/fulvestrant, with separate 95% confidence intervals. It does not report a comparative hazard ratio or sponsor-reported primary test.

Overall response rate and clinical benefit rate are posted as secondary outcomes. Their comparisons are unadjusted recalculations, with no reported analyses listed. The registry record does not report the analysis populations, missing-data methods, multiplicity strategy, or the trial's own sample-size rationale. The posted results support description of the observed outcome pattern, while leaving important comparative and methodological questions unresolved.