Hematologic adverse events following palbociclib (PAL) dose reduction in patients (pts) with hormone receptor‒positive (HR+)/human epidermal growth factor receptor 2‒negative (HER2‒) advanced breast cancer (ABC): Pooled analysis from randomized phase 2 and 3 studies.

1060Background: A previous pooled analysis showed that 36.9% of pts receiving PAL required dose reduction, most occurring during the first 6 mo of treatment and with decreasing frequency during subsequent 28-d treatment cycles (C). Previous data have also shown that PAL dose reductions do not affect efficacy (Im S-A, et al. ESMO Asia 2017). Methods: This analysis evaluated the frequency of hematologic adverse events (AEs) 30 d before and after dose reduction (during each treatment C1‒C6) among pts who required PAL dose reduction. Data were pooled from 3 randomized studies: PALOMA-1, a phase 2, open-label study of postmenopausal pts untreated for ABC receiving PAL+letrozole (L) or L alone; PALOMA-2, a phase 3, double-blind study of postmenopausal pts untreated for ABC receiving PAL+L or placebo (PBO)+L; PALOMA-3, a phase 3, double-blind study of pre- or postmenopausal pts who progressed on prior endocrine therapy receiving PAL+fulvestrant (F) or PBO+F. Results: A total of 311 pts with HR+/HER2‒ ABC require...