Retrospective registry of patients with locally advanced/metastatic HR+/HER2− breast cancer treated in clinical practice in Andalusia.

Background Limited data are available regarding the real-world effectiveness and safety of Cyclin Dependent Kinase 4/6 inhibitor (CDK4/6i) (palbociclib/ribociclib) just as a first-line treatment for patients with hormone receptor-positive/human epidermal growth factor receptor 2-negative (HR+/HER2‒) metastatic breast cancer (MBC). Objective To assess whether clinical or demographic characteristics limit access to first line CDK4/6i treatment in clinical practice in the Autonomous Community of Andalusia (Spain) between November 2017, and April 2020. In addition, effectiveness will be described in an exploratory analysis. Methods Physicians from 12 centers abstracted demographic and clinical characteristics, treatment and outcome data for women with HR+/HER2- MBC receiving and not receiving CDK4/6i in addition to hormonal treatment in the first-line setting a 3:1 proportion. Kaplan–Meier analysis estimated progression-free rates (PFRs) and survival rates (SRs). Results A total of 212 patients were included, of whom 175 (82.5%) were in the CDK4/6i treatment group and 37 (17.5%) were in the non-CDK4/6i treatment group (control group). CDK 4/6i treated patients were younger (p = 0.0011), and biopsies of the metastatic disease were done more frequently (p = 0.0454), with multiple metastases, and with differences in relation to the time of diagnosis of metastatic disease (p = 0.0304). The clinical benefit rate (CBR) was 82.3% in the CDK4/6i group and 67.8% in the control group. Median time to a progression event or death (PFS) was 20.4 months (95%CI 15.6–28) in the CDK4/6i group and 12.1 months (95%CI 7.9-not reached) in the control group. Conclusions Younger patients, biopsies of metastatic disease and with multiple metastases were more frequently treated with CDK4/6i.