Efficacy and safety of selective cyclin-dependent kinases 4/6 inhibitors in hormone-receptor-positive, HER2-negative advanced breast cancer – results from a real-world setting

BACKGROUND Selective cyclin-dependent kinases 4/6 inhibitors (CDKi) have become the standard of care in patients with hormone receptor (HR)-positive, HER2-negative advanced breast cancer (ABC). We performed retrospective analysis in patients treated with CDKi in the first year of their routine clinical use in Slovenia. METHODS The primary goals were time-to-treatment failure (TTF) and overall survival (OS), analysed via Kaplan-Meier method, the secondary goals were clinical benefit rate (CBR) and safety. RESULTS Overall, 218 patients' data were evaluated. The median age was 61.8 years (30.6-84.6). The median number of previous ET lines for ABC was 2 (range 0-5). At the time of inclusion, 128 patients (58.7%) had visceral metastases, 45 patients (20.6%) had bone-only disease. At the median follow-up of 15.2 months, disease progressed in 74 patients and 60 patients died. The median TTF was 8.3 months for the whole group, 19.3, 10.3 and 5.5 months for patients treated in the first-, second- and further lines of systemic therapy, respectively. The median OS from the start of CDKi treatment was not reached in any of the groups. CBR was 59.6% for the whole group, 42.7% for further lines of therapy. The most common grade 3/4 adverse event was neutropaenia in 108 patients (49.5%), followed by an increase of hepatic aminotransferases in 13 patients (6.0%). CONCLUSIONS Even in the diverse real-world population treatment with CDKi in combination with ET showed clinical benefit, most prominently in the first- and second lines of systemic therapy.