Abstract 443: Blood-based genotyping and clinical outcomes in patients with advanced breast cancer receiving the CDK4/6 inhibitor palbociclib in real-world settings: Results from POLARIS
Authors: Bardia Aditya , Blum Joanne L. , McCune Steven L. , Patel Kamal , Frank Richard C. , Mosalpuria Kailash , Karuturi Meghan S. , Shabazz Lloyd A. , Rocque Gabrielle B. , Liu Yuan , Zhang Zhe , Wang Jian , Wang Yao , Tripathy Debu 
Published: August 2019

Abstract
Background:POLARIS is a prospective, real-world (RW) study of palbociclib (PAL) in patients (pts) with hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2–) advanced breast cancer (ABC) in the US and Canada. Analyses include evaluating the association between circulating tumor DNA (ctDNA) and clinical response to PAL.
Methods: All pts provided informed consent. Blood samples are collected on day 1 of each 4-wk cycle for 6 cycles, at day 1 of every 2-3 cycles, and end of treatment. ctDNA is sequenced using the Guardant360 platform for somatic single-nucleotide variants in complete or critical exons of 73 genes. Analyses include association between clinical outcomes and ctDNA mutation frequencies at baseline and change from baseline to cycle 2, day 1 (C2D1), stratified by line of prior therapy.
Results: As of July 2018, 127 pts had ≥1 evaluable ctDNA measurement. Of these, 104 had baseline and C2D1 results; 96 had tumor response assessed. The most common mutations at baseline were PIK3CA (41%), TP53 (33%), and ESR1 (20%). PAL was associated with a decline in mutation frequency of PIK3CA, TP53, and ESR1alleles but not all genes, highlighting differential response based on genomic profile and clonal heterogeneity (Table). Overall, fast progressors (progression &lt;6 mo, n=19) tended to have higher baseline ctDNA values and displayed smaller decreases in ctDNA at C2D1 than slow progressors (progression ≥6 mo, n=4).
Conclusions: This study is among the first to provide RW data on blood-based genotyping. Interim data indicate that genomic architecture and longitudinal changes may be predictive and prognostic in pts with HR+/HER2– ABC receiving PAL. Updated data from 239 pts will be presented, including association between individual ctDNA mutation dynamics, clonal heterogeneity, and clinical outcomes (therapeutic response and progression-free survival). Pfizer; NCT03280303
Change from baseline in ctDNA mutation frequencyMutationOverall (n=104)*First Line (n=70)Second Line and Later (n=34)Baseline, n (%)†C2D1, n (%)†Baseline, n (%)†C2D1, n (%)†Baseline, n (%)†C2D1, n (%)†PIK3CA43 (41)26 (25)27 (39)14 (20)16 (47)12 (35)TP5334 (33)27 (26)23 (33)17 (24)11(32)10 (29)ESR121 (20)11 (11)9 (13)3 (4)12 (35)8 (24)ARID1A19 (18)14 (13)13 (19)7 (10)6 (18)7 (21)NF111 (11)11 (11)7 (10)6 (9)4 (12)5 (15)BRCA210 (10)10 (10)8 (11)7 (10)2 (6)3 (9)GATA310 (10)5 (5)8 (11)5 (7)2 (6)O (O)None detected13 (13)24 (23)7 (10)20 (29)6 (18)4 (12)ctDNA=circulating tumor DNA; C2D1=cycle 2, day 1. *Patients with both baseline and C2D1 ctDNA data available. †Percentages are relative to the corresponding number of patients (n).
Citation Format: Aditya Bardia, Joanne L. Blum, Steven L. McCune, Kamal Patel, Richard C. Frank, Kailash Mosalpuria, Meghan S. Karuturi, Lloyd A. Shabazz, Gabrielle B. Rocque, Yuan Liu, Zhe Zhang, Jian Wang, Yao Wang, Debu Tripathy. Blood-based genotyping and clinical outcomes in patients with advanced breast cancer receiving the CDK4/6 inhibitor palbociclib in real-world settings: Results from POLARIS [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 443.