Adding palbociclib to fulvestrant prolongs progression-free survival (PFS) compared with fulvestrant alone among pre- and post-menopausal women with hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative metastatic breast cancer, according to research published in the Journal of Global Oncology (published online April 11, 2017; doi:10.1200/JGO.2016.008318).
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Treatment of metastatic breast cancer with endocrine therapy is considered standard of care. Treating patients who become resistant to endocrine therapy or who have disease progression within 12 months of completing adjuvant endocrine therapy is a challenge yet to be thoroughly evaluated in a clinical setting.
Researchers from various Asian countries conducted a double-blind phase III trial to evaluate the effects of palbociclib plus fulvestrant in endocrine therapy-resistant patients. A total of 521 pre- and post-menopausal women with HR-positive/HER2-negative metastatic breast cancer with disease progression on endocrine therapy were randomly assigned to receive either palbociclib plus fulvestrant (n = 71) or placebo plus fulvestrant (n = 31). One previous chemotherapy regimen was permitted prior to enrollment.
Results of the analysis showed that treatment with palbociclib plus fulvestrant significantly improved PFS compared with placebo plus fulvestrant. Median PFS was not reached in the palbociclib cohort (95% CI, 9.2 months-not reached), whereas median PFS was 5.8 months in the fulvestrant only cohort (95% CI, 3.5-9.2 months).
Researchers acknowledged an increased risk of adverse events among the patients in the palbociclib cohort. Grade 4 neutropenia (92%) and leukopenia (29%) occurred in this population, as well as febrile neutropenia in 4.1% of patients. There were no observed grade 4 adverse events in the fulvestrant only cohort.
Implications of the study suggest that adding palbociclib to fulvestrant is a reasonable treatment option for women with HR-positive/HER2-negative metastatic breast cancer who have progressed on standard endocrine therapy. Further research is needed to evaluate the combination regimen in a larger sample of patients. – Zachary Bessette
