OBJECTIVES: The aim of our study was to evaluate medication adherence and identify influencing factors in patients undergoing palbociclib for advanced or metastatic breast cancer.

METHODS: Palbociclib, the first CDK4/6 inhibitor approved by the FDA, received unconditional approval from the National Agency for Medicines and Medical Devices in Romania for inclusion in the Positive Drug List in November 2017. Our study included patients diagnosed with breast cancer who had received electronic prescriptions from their oncologists. Medication adherence was assessed using the Proportion of Days Covered (PDC) method. To explore potential correlations between medication adherence and patient age and gender, Spearman's coefficients were calculated. Statistical analysis was performed using GraphPad Prism 10.1, with a significance level set at p < 0.05 (two-tailed).

RESULTS: Between January 2018 and December 2022, a total of 330 patients were prescribed CDK4/6 inhibitors, of which 55% (180 patients) received palbociclib. The eligible patients included in our study had an average follow-up period of 14.6 ± 12.5 months. Among patients treated with palbociclib, no significant correlation was found between adherence and age (rho = 0.07, p = 0.35) or gender (rho = -0.144, p = 0.054). However, a significant correlation was observed with the duration of follow-up (rho = -0.304, p < 0.0001). The adherence rates for palbociclib were 92.5% ± 13.7%. Most patients received combination therapy with letrozole (46%) and exemestane (13%). The absence of adherence barriers related to costs was noted, as the drugs were provided free of charge and fully covered by the Romanian National Oncology Program, reimbursed by the National Health Insurance House.

CONCLUSIONS: While high adherence rates were observed among patients treated with palbociclib, it is important to note that the collected data FROM THE Romanian National Health Insurance House were limited, lacking information on potential adverse reactions that might lead to treatment discontinuation.