Real-world treatment durations, subsequent treatments, and switching of CDK4/6 inhibitors among patients with HR+/HER2- metastatic breast cancer.

BACKGROUND

Cyclin-dependent kinase 4/6 inhibitors (CDK4/6is), palbociclib, ribociclib, and abemaciclib, are approved for HR+/HER2- metastatic breast cancer (mBC). This real-world study evaluated treatment durations and subsequent treatments of patients with HR+/HER2- mBC who received CDK4/6is plus aromatase inhibitor (AI) in the United States.

METHODS

Adult patients with HR+/HER2- mBC who initiated first-line (1L) CDK4/6is plus AI (February 2015-July 2024) were selected from the US-based Flatiron Health Research database. Stabilized inverse probability of treatment weighting (sIPTW) was conducted. Kaplan-Meier analyses estimated treatment durations.

RESULTS

Of 11 557 patients, 8109, 2006, and 1442 received 1L palbociclib, ribociclib, and abemaciclib, respectively. After sIPTW, treatment duration was longer for the palbociclib group (median: 20.7 months) than the ribociclib (18.3 months) and abemaciclib (17.1 months) groups (ribociclib vs palbociclib: hazard ratio [HR] = 1.12 [95% confidence interval (CI), 1.05-1.20], P = .0008; abemaciclib vs palbociclib: HR = 1.13 [95% CI, 1.05-1.22], P = .0012). Treatment durations were similar between the ribociclib and abemaciclib groups (HR = 1.01 [95% CI, 0.92-1.11], P = .8280). Twelve-month treatment discontinuation rates were higher among patients initiating ribociclib or abemaciclib, at 39.4% and 41.1%, respectively, than among patients initiating palbociclib (33.3%). In the analysis of patients who initiated palbociclib, ribociclib, or abemaciclib from 2017 onward, 49.9%, 37.3%, and 39.4%, respectively, received subsequent treatments; CDK4/6i-containing regimens accounted for 42.3%, 54.1%, and 55.7%, respectively; notably, more patients initially treated with ribociclib or abemaciclib transitioned to palbociclib than those who switched oppositely.

CONCLUSIONS

Treatment durations, discontinuation rates, and subsequent treatments differ between CDK4/6is for HR+/HER2- mBC in US routine clinical practice.

CLINICAL TRIAL REGISTRATION NUMBER: NCT06495164.