To assess efficacy and safety of palbociclib plus fulvestrant in Asians with endocrine therapy-resistant metastatic breast cancer.

The Palbociclib Ongoing Trials in the Management of Breast Cancer 3 (PALOMA-3) trial, a double-blind phase III study, included 521 patients with hormone receptor-positive/human epidermal growth factor receptor 2-negative metastatic breast cancer with disease progression on endocrine therapy. Patient-reported outcomes (PROs) were assessed on study treatment and at the end of treatment.

This preplanned subgroup analysis of the PALOMA-3 study included premenopausal and postmenopausal Asians taking palbociclib plus fulvestrant (n = 71) or placebo plus fulvestrant (n = 31). Palbociclib plus fulvestrant improved progression-free survival (PFS) compared with fulvestrant alone. Median PFS was not reached with palbociclib plus fulvestrant (95% CI, 9.2 months to not reached) but was 5.8 months with placebo plus fulvestrant (95% CI, 3.5 to 9.2 months; hazard ratio, 0.485; 95% CI, 0.270 to 0.869; = .0065). The most common all-cause grade 3 or 4 adverse events in the palbociclib arm were neutropenia (92%) and leukopenia (29%); febrile neutropenia occurred in 4.1% of patients. Within-patient mean trough concentration comparisons across subgroups indicated similar palbociclib exposure between Asians and non-Asians. Global quality of life was maintained; no statistically significant changes from baseline were observed for patient-reported outcome scores with palbociclib plus fulvestrant.

This is the first report, to our knowledge, showing that palbociclib plus fulvestrant improves PFS in asian patients. Palbociclib plus fulvestrant was well tolerated in this study.