Background: In the double-blind, phase 3 PALOMA-3 study, palbociclib-fulvestrant significantly prolonged progression-free survival versus placebo-fulvestrant in patients with hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2-) metastatic breast cancer (MBC) whose disease had progressed on prior endocrine therapy. The present study evaluated the efficacy, safety, and pharmacokinetics of palbociclib plus fulvestrant in Japanese patients enrolled in PALOMA-3.
Methods: Pre/peri/postmenopausal women with HR+/HER2- MBC were randomized 2:1 to fulvestrant (500 mg) and either palbociclib (125 mg/day; 3 weeks on/1 week off; n = 347) or placebo (n = 174). Prespecified exploratory analyses compared the efficacy (data cutoff: October 23, 2015), safety, and pharmacokinetics (data cutoff: December 5, 2014) in Japanese women versus the overall population.
Results: A total of 35 Japanese women were randomized to palbociclib-fulvestrant (n = 27) or placebo-fulvestrant (n = 8). Median progression-free survival was 13.6 months (95% CI, 7.5-not estimable) in the Japanese palbociclib-fulvestrant group and 11.2 months (95% CI, 5.6-not estimable) in the placebo-fulvestrant group. The most common adverse event (AE) in Japanese patients was neutropenia (all grades, 93%); no discontinuations were due to an AE. Geometric mean trough concentration values (within-subject mean steady state) for palbociclib were similar for Japanese Asian (excluding Japanese), and non-Asian patients (84.4 ng/mL, 86.3 ng/mL, and 74.8 ng/mL, respectively).
Conclusion(s): The results for the overall population and Japanese patients in PALOMA-3 suggest that palbociclib plus fulvestrant was effective and well tolerated in Japanese patients with HR+/HER2‒ MBC whose disease had progressed on prior endocrine therapy (Pfizer; NCT01942135).
Keywords: Advanced or metastatic breast cancer; Fulvestrant; Hormone receptor positive; Human epidermal growth factor receptor 2-negative; Japanese subgroup; Palbociclib.