Long-term safety profile of palbociclib (P) in combination with letrozole (L) as first-line treatment for postmenopausal patients with ER+ and HER2- advanced breast cancer (ABC) (PALOMA-1/TRIO-18).

570 Background: P is a selective and reversible oral CDK4/6 inhibitor. In a randomized phase (ph) I/II trial comparing P plus L (P + L) to L alone in patients (pts) with ER+ and HER2– ABC who had not received any prior systemic therapy for their ABC (Study 1003), P + L demonstrated significantly longer progression-free survival (PFS) vs L (20 vs 10 m; HR = 0.488, P=0.0004). Methods: We analyzed reported Adverse Events (AE) from Study 1003 by time interval (0-6m, 6-12m, 12-24, and >24m), cumulatively (12 m, 24 m time points) and assessed latency (event onset) of pertinent Adverse Drug Reactions (ADRs). Results: As of Nov 2013, 95 pts received P + L. The median duration of treatment for P was 374 d (range: 63-1682) for Ph1 (n=12) and 420 d (range: 7-1242) for ph2 (n=83). The 6 m interval analysis of the most common (>15%) ADRs (Table 1) indicated that ADRs tend to occur with greater frequency within the first 6 m with some decrease in incidence over time. Comparison of the cumulative incidences between the ...