Effectiveness and Safety of Palbociclib plus Endocrine Therapy in Hormone Receptor-Positive, HER2-Negative Metastatic Breast Cancer: Real-World Results.

Background: Real-world data are critical to demonstrate the reproducibility of evidence and the external generalizability of randomized clinical trials. Palbociclib is an oral small-molecule inhibitor of cyclin-dependent kinases 4/6 that has been shown to improve progression-free survival when combined with letrozole or fulvestrant in phase 3 clinical trials.

Objective: To evaluate real-world outcomes in patients with metastatic breast cancer who received palbociclib in combination with endocrine therapy in routine clinical practice.

Methods: In this retrospective observational multicentre study, data were evaluated for all women with metastatic breast cancer who were treated with palbociclib from April 2017 to September 2019. Treatment response was assessed through progression-free survival according to the Response Evaluation Criteria in Solid Tumors, version 1.1.

Results: Fifty-three patients were included in the study, with median age 57 years (range 31-87 years). For all patients treated with palbociclib, median progression-free survival by the end of the study period was 14.4 months (95% confidence interval [CI] 6.2-22.2 months). Twenty-three women who received palbociclib as a first-line treatment did not experience progression-free survival; for these patients, the median treatment duration was 12.1 months (95% CI 1.4-28.0 months). For the 23 patients who received palbociclib as second-line therapy for metastatic breast cancer, median progression-free survival was 13.3 months (95% CI 4.1-22.4 months). Among the 7 women who received palbociclib as third-line therapy, median progression-free survival was 6.0 months (95% CI 0.9-11.1 months). The most common adverse events were hematologic, with grade 3 or 4 neutropenia occurring in 20 (38%) of the 53 patients.

Conclusions: This study provides data from a real-world setting that match the results of previous studies in terms of effectiveness (i.e., progression-free survival) when palbociclib plus endocrine therapy was used as second- or third-line treatment. Palbociclib had appropriate tolerability and a profile of easily manageable adverse effects, with none of the patients suspending their treatment because of toxic effects.