Background The first-in-class oral inhibitor of cyclin-dependent kinases 4 and 6 (CDK4/6) palbociclib, combined with hormonal therapy, is a new standard of treatment in the first and second line for hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2-) metastatic breast cancer (mBC).

Purpose To describe the effectiveness and safety of palbociclib combination therapy for mBC in clinical practice.

Material and methods Retrospective and observational study in which the effectiveness and safety of palbociclib was tested by reviewing medical and pharmaceutical records of all patients treated with the drug from December 2015 until April 2018 in a tertiary hospital. Dispensation data was obtained from the Pharmacy Department’s software, Farmatools. Collected data included: age, ECOG performance status, number of cycles received, duration and prior lines of treatment. Effectiveness endpoint was progression-free survival (PFS) according to RECIST version 1.1. Adverse events (AEs) related to treatment with palbociclib and registered in the patient’s medical records were included in the study. Toxicity was evaluated as defined by the NCI-CTCAE, version 4.0.

Conclusion A significant difference in PFS was observed compared to published clinical trials PALOMA-2 (PFS 24.8 months) and PALOMA-3 (PFS 11.2 months). Otherwise, palbociclib showed a similar safety profile. However, further studies are required to establish effectiveness in clinical practice as 19/29 patients are still receiving treatment.

References and/or acknowledgements 1. Palbociclib: EPAR-Summary for the public. EMA.

2. Pivotal studies PALOMA-2 and PALOMA-3.

No conflict of interest.