Abstract 246P
Background
Palbociclib is a cyclin-dependent kinase (CDK) 4/6 inhibitor indicated for use in combination with aromatase inhibitors or fulvestrant for patients with hormone receptor-positive (HR+) human epidermal growth factor receptor 2 (HER2)-negative metastatic breast cancer (MBC). The Swedish Ibrance Registries Insights (SIRI) study investigated real-world dose patterns using a nationwide Swedish cohort of palbociclib-treated MBC patients.
Methods
This was a retrospective study utilizing population-based Swedish Health Data Registers. The cohort included all patients ≥ 18 years with ≥ 1 filled prescription of palbociclib from January 2017 – June 2020. Minimum follow-up was 3 months. Starting dose and dose changes for the full population, for subgroups, in total and over time, was investigated.
Results
1226 patients with palbociclib prescription were identified, 10 were men. Mean (SD) age at treatment initiation was 65 (11) years. 11% of patients had de novo MBC. Most patients were initiated on 125 mg (86.8%), with a lower share for older patients (80%), and a falling share over time (Table). 43.5% of patients had ≥1 dose reduction, with a falling share over time (47.1% in 2017; 35.2% in 2020). The share of patients starting on 125 mg reduced to 100 mg and 75 mg (final doses) was 26.6% and 19.4%, respectively, whereas 28% of patients starting on 100 mg reduced to 75 mg. Endocrine therapy backbone did not affect dose patterns. Younger patients (<50 years) starting on 125 mg were more frequently down dosed to a final dose of 100 mg (34% vs 25.7% for age 50-69 and 26.1% for age ≥70), whereas dose reduction from 125 to 75 mg increased with age (<50: 12%; 50-69: 18%; ≥70: 23.6%). Table: 246P
| Palbociclib starting year | ||||
| 2017 | 2018 | 2019 | 2020 | |
| N | 140 | 500 | 393 | 193 |
| Starting dose, % (n) | ||||
| 75 mg | 0% (0) | 2.6% (13) | 3.6% (14) | 5.2% (10) |
| 100 mg | 2.7% (4) | 9.2% (46) | 11.5% (45) | 15.5% (30) |
| 125 mg | 97.1% (136) | 88.2% (441) | 85% (334) | 79.3% (153) |
Conclusions
Most Swedish palbociclib-treated patients were initiated on the recommended starting dose, but a trend towards a reduced starting dose was observed over time. In total, dose reductions appear to be slightly more common in clinical practice, but with a falling trend approaching clinical trial findings over time.
Clinical trial identification
Editorial acknowledgement
Legal entity responsible for the study
Pfizer Innovations AB.
Funding
Pfizer Innovations AB.
Disclosure
H. Fues Wahl: Financial Interests, Institutional, Project Lead, HFW is an employee of Quantify Research and was a paid consultant to Pfizer for this research: Quantify Research. R. Lauppe: Financial Interests, Institutional, Project Lead, RL is an employee of Quantify Research and was a paid consultant to Pfizer for this research: Quantify Research. M. Lilja: Financial Interests, Institutional, Other, ML is an employee of Quantify Research and was a paid consultant to Pfizer for this research: Quantify Research. D. Nyqvist: Financial Interests, Institutional, Stocks/Shares, DN is an employee of Pfizer: Pfizer Innovations AB. M. Jakobsson: Financial Interests, Institutional, Stocks/Shares, MJ is an employee of Pfizer: Pfizer Innovations AB. All other authors have declared no conflicts of interest.