Efficacy of Palbociclib Combinations in Hormone Receptor–Positive Metastatic Breast Cancer Patients After Prior Everolimus Treatment

Purpose Outcome data on hormone receptor positive (HR+), human epidermal growth factor receptor 2 (HER2) nonamplified (HER2−) metastatic breast cancer (MBC) treated with palbociclib after treatment with everolimus are lacking. The PALOMA-3 trial, showing benefit of palbociclib plus fulvestrant compared to fulvestrant alone in HR+HER2− MBC after progression while receiving endocrine therapy excluded women previously treated with everolimus. The objective of this study was to examine outcomes of HR+HER2− MBC with prior exposure to everolimus while receiving palbociclib-based therapy. Patients and Methods A retrospective, single-institute review was conducted of HR+HER2− MBC from January 2014 to November 2016 in patients treated with palbociclib after prior treatment with everolimus. Progression-free survival (PFS) was defined as the time from initiation of palbociclib to the date of progression as determined by the treating physician based on radiologic, biochemical, and/or clinical criteria. Response rates were determined on the basis of available radiologic data. Objective response rate (ORR) was defined as the rate of any complete or partial responses; clinical benefit rate (CBR) was the rate of complete response, partial response, or stable disease for at least 24 weeks. Results Twenty-three patients with a mean (range) age of 68 (42-81) years were identified. Kaplan-Meier estimate showed median PFS of 2.9 months (95% confidence interval, 2.1-4.2); ORR was 0 of 23 and CBR was 4 (17.4%) of 23. In the PALOMA-3 trial, median PFS, ORR, and CBR of palbociclib cohort were 9.5 months (95% confidence interval, 9.2-11.0), 19%, and 67%, respectively. Conclusion There is a limited clinical activity of palbociclib combinations after progression with everolimus combination therapy. Further studies are necessary to confirm these findings.