Circulating Tumor DNA Genotyping of Intrinsic and Acquired Gene Alterations in Patients With Advanced Breast Cancer Receiving Palbociclib: Biomarker Results From POLARIS Study

Patients without altered <i>ESR1</i>, <i>PIK3CA</i>, <i>CCND1</i>, or <i>FGFR1</i> at baseline had better rwPFS than patients with altered genes. Genotyping analysis of ctDNA over time highlights the emergence of mutations in estrogen receptor and cell cycle pathways under selective therapeutic pressure and could guide monitoring and therapeutic sequencing for patients with HR+/HER2- ABC.