Abstract P5-21-25: Efficacy and safety of palbociclib (PAL) + letrozole (LET) as first-line therapy in estrogen receptor–positive (ER+)/human epidermal growth factor receptor 2–negative (HER2−) advanced breast cancer (ABC): Findings by geographic region from PALOMA-2
Authors: Gelmon KA , Castrellon A , Joy AA , Walshe JM , Ettl J , Mukai H , Park IH , Lu DR , Mori A , Bananis E , Diéras V , Finn RS 
Published: February 2018

BACKGROUND: Previous findings from the PALOMA-2 study (N=666) demonstrated the efficacy and safety of PAL+LET as first-line ABC therapy versus placebo (PBO)+LET (Finn et al, NEJM. 2016). This analysis evaluated the efficacy and safety of PAL+LET by geographic region (North America [NA], Europe [EU], and Asia Pacific [AP]; data cutoff: Feb 26, 2016).

METHODS: Women with ER+/HER2– ABC who had not received prior systemic treatment in the advanced setting were randomized 2:1 to PAL (125 mg/d oral [3 wks on, 1 wk off])+LET (2.5 mg once daily) or PBO+LET.

RESULTS: This analysis included 267 patients from NA, 307 from EU, and 92 from AP. At baseline, demographics and disease characteristics generally were similar between regions. In the overall population (Table 1), PAL+LET demonstrated improvements versus PBO+LET in progression-free survival (PFS), objective response rate (ORR), and clinical benefit response rate (CBR). Similarly, PFS was longer and ORR and CBR were higher with PAL+LET versus PBO+LET in NA, EU, and AP subgroups (Table 1). All-grade treatment-emergent adverse events (AEs) (PAL+LET/PBO+LET) occurred in 99%/99% of patients in NA, 98%/92% in EU, and 100%/96% in AP. In the PAL+LET arm, neutropenia (all-grade/grade ≥3) was the most common AE in all regions. The incidence of neutropenia was numerically higher in AP (91%/84%) compared with NA (73%/65%) and EU (81%/62%). Grade 3 or 4 febrile neutropenia occurred in 4 (2%) NA patients, 4 (2%) EU patients, and no AP patients in the PAL+LET arm and in no patients in any of the regions in the PBO+LET arm.

CONCLUSIONS: PAL+LET showed improvement versus PBO+LET in PFS, ORR, and CBR in patients with ER+/HER2- ABC in NA, EU, and AP, with comparable magnitude of benefit between regions. With PAL+LET, neutropenia was the most commonly reported AE in all regions, with a numerically higher incidence reported in AP versus NA or EU; the safety profile was similar to previously reported results in the overall population.

Funding: Pfizer (NCT01740427)

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Table 1. PFS, ORR, and CBR Median PFSPFS HRORR,* %CBR,* % (95% CI), mo(95% CI)(95% CI)(95% CI)Overall Population    PAL+LET24.8 (22.1-NE)0.58 (0.46-0.72); P&lt;0.00155.3 (49.9-60.7)84.3 (80.0-88.0)PBO+LET14.5 (12.9-17.1) 44.4 (36.9-52.2)70.8 (63.3-77.5)NA    PAL+LET24.2 (17.5-NE)0.61 (0.43-0.85)54.3 (45.3-63.2)80.3 (72.3-86.8)PBO+LET13.8 (10.3-22.1) 50.6 (39.1-62.1)67.1 (55.6-77.3)EU    PAL+LET24.8 (22.1-NE)0.57 (0.41-0.80)55.6 (47.6-63.5)87.5 (81.4-92.2)PBO+LET16.5 (11.3-19.6) 38.2 (26.7-50.8)73.5 (61.4-83.5)AP    PAL+LET22.2 (19.4-25.7)0.49 (0.27-0.87)56.9 (42.2-70.7)84.3 (71.4-93.0)PBO+LET13.9 (7.4-22.0) 41.7 (22.1-63.4)75.0 (53.3-90.2)HR=hazard ratio; NE=not estimable; OR=objective response.*Confirmed OR in patients with measurable disease.

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Citation Format: Gelmon KA, Castrellon A, Joy AA, Walshe JM, Ettl J, Mukai H, Park IH, Lu DR, Mori A, Bananis E, Diéras V, Finn RS. Efficacy and safety of palbociclib (PAL) + letrozole (LET) as first-line therapy in estrogen receptor–positive (ER+)/human epidermal growth factor receptor 2–negative (HER2−) advanced breast cancer (ABC): Findings by geographic region from PALOMA-2 [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P5-21-25.