Real-world evidence from Japan regarding survival outcomes and treatment sequence in patients receiving CDK4/6 inhibitor plus endocrine therapy as first- or second-line treatment for hormone receptor-positive, HER2-negative advanced or metastatic breast cancer.

BACKGROUND

A cyclin-dependent kinase 4/6 inhibitor (CDK4/6i) plus endocrine therapy (ET) is a current standard first-/second-line treatment for hormone receptor (HR)-positive, HER2-negative advanced/metastatic breast cancer (AMBC). We aimed to provide real-world evidence regarding CDK4/6i therapy in this population.

METHODS

In this multicenter observational study, data from patients who had started CDK4/6i therapy between January 1, 2019, and December 31, 2021, as first-/second-line treatment for AMBC were used; real-world progression-free survival (rwPFS), chemotherapy-free survival, and overall survival were analyzed using the Kaplan-Meier method. Additionally, data were analyzed by separating patients with treatment-free interval (TFI) < 12 months (deemed resistant to ET) from the first-line treatment group (hereafter, the exclusive first-line treatment group).

RESULTS

Data from 745 patients were analyzed. Compared with palbociclib, abemaciclib was used in younger patients and those with expected poor prognosis. Median rwPFS was 36.8, 17.8, and 31.4 months in patients with de novo stage IV disease, TFI < 12 months, and TFI ≥ 12 months, respectively, in the first-line treatment group, and 17.4 months in the second-line treatment group. In the exclusive first-line treatment group, median rwPFS of the subsequent treatment after initial CDK4/6i plus ET was < 7 months, regardless of the type of subsequent treatment; prognosis was especially poor in those who were switched to chemotherapy.

CONCLUSIONS

The real-world survival outcomes found in this study for patients receiving first-/second-line CDK4/6i therapy were consistent with those of randomized phase 3 studies. As outcomes of subsequent treatment after initial CDK4/6i plus ET remain insufficient, further improvement in treatment is necessary.