Efficacy of palbociclib after everolimus in hormone receptor-positive, HER2-negative advanced breast cancer.

e13030 Background: Palbociclib and other selective cyclin-dependent kinases 4 and 6 inhibitors in combination with endocrine therapy (ET) have become the standard of care in the treatment of patients with hormone receptor-positive (HR+), HER2-negative advanced breast cancer (ABC). Their role in the first and second line of therapy is well established, whereas their use in subsequent lines and after treatment with everolimus remains unclear. Methods: We performed retrospective observational study of all patients who initiated treatment with palbociclib at the Institute of Oncology Ljubljana between March 8, 2018 and March 8, 2019 and received at least two prior lines of treatment for ABC. We collected individual patient data from electronic medical records. Patients were divided in two groups – everolimus-pretreated (group A) and everolimus-naïve (group B). The primary study outcomes were clinical benefit rate (CBR), time to treatment failure (TTF) and overall survival (OS). Results: Overall, 65 patients´ data was evaluated. The majority of patients (n = 50, 76.9%) received palbociclib in combination with fulvestrant, others (n = 15, 23.1%) with aromatase inhibitors. There were 25 (38.5%) patients in group A and 40 (61.5%) in group B. Patients´ and previous treatment characteristics are shown in table. CBR was the same, 40%, in both groups. The median follow-up time was 14.9 months. The median TTF was 5.28 months for the whole group, 5.0 months for everolimus-pretreated and 5.5 months for everolimus-naïve group (p = 0.7). The median OS was 18.1 months for the whole group, 14 months for everolimus-pretreated and 18.1 months for everolimus- naïve group (p = 0.7). Conclusions: Patients with HR+, HER-2-negative ABC benefit from addition of palbociclib to ET after two lines of prior systemic therapy. The benefit remained unchanged if the patients were previously treated with everolimus. [Table: see text]