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The content of this website has been produced in line with the IBRANCE® Summary of Product Characteristics. IBRANCE® (palbociclib) Prescribing Information for the UK click here. Adverse event reporting information can be found at the bottom of the page.
Duration of treatment analysis
STUDY OBJECTIVE
To understand treatment durations, discontinuation rates, subsequent treatments, and treatment switches in patients with HR+/HER2- mBC receiving 1L palbociclib, ribociclib or abemaciclib in combination with an AI in US routine clinical practice.1
STUDY DESIGN
*1L CDK4/6i treatment duration was defined as the time from the start of the specific CDK4/6i to discontinuation of treatment or death during the 1L. Patient data were derived from the Flatiron Economic Health Research Database, a de-identified database with over 750,000 patients with breast cancer represented at the time of this study.1
†Subsequent treatment was defined as a change in systemic therapy triggering a line advancement, with the exception of changes in AI (i.e., a change from one AI to another did not trigger a line advancement). Subsequent treatments for mBC were examined in patients who started 1L treatment in 2017 onward, when the three CDK4/6is were all approved in the US.
‡CDK4/6i switching was defined as changing CDK4/6i with or without changing the AI partner.
PATIENT CHARACTERISTICS
After sIPTW, baseline demographics and clinical characteristics were generally balanced between the palbociclib, ribociclib and abemaciclib groups*1
*The balance in these baseline characteristics was assessed using a standardised mean differences approach, with values ≥0.1 indicating a non-negligible imbalance.1 Standard difference data not shown. More patients were eligible for the palbociclib cohort, as palbociclib was the first CDK4/6i approved in the US (in 2015), followed by in 2017 by both ribociclib and abemaciclib.1
†Visceral disease is defined as metastatic disease in the lung and/or liver. Patients could have had other sites of metastases.
‡Bone-only disease is defined as metastatic disease in the bone only.
RESULTS: Treatment duration and discontinuation rates
These findings were consistent with those observed in the unadjusted and sensitivity analyses‡
‡ Treatment durations were compared in the unadjusted analyses and after stabilised inverse probability treatment weighting (sIPTW). A sensitivity analysis of duration of treatment was conducted with a multivariable Cox proportional hazards model that used these same variables as covariates. A separate analysis was carried out in patients who started 1L treatment from 2017 onward.
*1L CDK4/6i treatment duration was defined as the time from the start of the specific CDK4/6i to discontinuation of treatment or death during the 1L. Treatment durations were estimated using the Kaplan-Meier method and Cox proportional hazards models were used to calculate HRs and corresponding 95% CIs. Patients were censored at the earlier of their last medical activity or data cut-off if they were alive and had not experienced treatment discontinuation. Patient cohort included those initiated on treatment from 2015–2024.
†Descriptive statistical analysis only
STUDY LIMITATIONS1
• Retrospective analysis of electronic health records may have inaccurate or incomplete data capture.
• Information about dose adjustments or reasons for discontinuation and subsequent treatments (e.g., disease
progression or toxicity) were not available in the data source at the time of data analysis
• Although sIPTW and multivariable analyses were utilised to mitigate potential bias in this study, the effects of
unmeasured covariates, such as socioeconomic factors and prior adjuvant therapies, could not be excluded
• Compared with the IBRANCE group, the ribociclib and abemaciclib groups had smaller sample sizes and
shorter follow-up durations
• Findings from the data source may not generalise to other patient populations
1L, first-line; Al, aromatase inhibitor; CDK4/6, cyclin-dependent kinase 4/6; DOT, duration of treatment; HER2-, human epidermal growth factor receptor 2-negative; HR+, hormone receptorpositive; mBC, metastatic breast cancer;KM, Kaplan-Meier;US, United States; ECOG PS, Eastern Cooperative Oncology Group performance status; IQR, interquartile range; SD, standard deviation; sIPTW, stabilised inversed probability of treatment weighting; HR, hazard ratio; PAL, palbociclib; RIB, ribociclib; ABE, abemaciclib.
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References
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PP-UNP-GBR-13971. December 2025