Overall survival (OS) with first-line palbociclib plus letrozole (PAL+LET) versus placebo plus letrozole (PBO+LET) in women with estrogen receptor–positive/human epidermal growth factor receptor 2–negative advanced breast cancer (ER+/HER2− ABC): Analyses from PALOMA-2.

LBA1003 Background: PAL was the first cyclin-dependent kinase 4/6 (CDK4/6) inhibitor approved for ER+/HER2– ABC based on the randomized, phase 2 PALOMA-1 study. PALOMA-2 is a randomized, double-blind, phase 3 trial in first-line ER+/HER2– ABC that confirmed a clinically and statistically significant improvement in progression-free survival (PFS) with PAL+LET versus PBO+LET (median PFS, 27.6 vs 14.5 months; hazard ratio, 0.56 95% CI, 0.46–0.69; P12 months, median OS (95% CI) was 66.3 months (52.1–79.7) in the PAL+LET arm (n=179) and 47.4 months (37.7–57.0) in the PBO+LET arm (n=93); hazard ratio, 0.728 (95% CI, 0.528-1.005). No new safety findings were observed. Conclusions: PALOMA-2 met its primary endpoint of improving PFS but not the secondary endpoint of OS. Pts receiving PAL+LET had numerically longer OS compared to PBO+LET, but the results were not statistically significant. Funding: Pfizer Inc (NCT01740427) Clinical trial information: NCT01740427.