LAUSR

1080Background: Circulating DNA fragments (ctDNA) are using to longitudinal non-invasive molecular monitoring and resistance mechanism interrogation of the disease by detecting genomic alteration change and clonal evolution including somatic mutation and copy number alteration. Methods: We performed a retrospective analysis of blood samples from mBC patients (pts) collected at pre-treatment, on-treatment, and disease progression. A highly sensitive, plasma-derived ctDNA-based NGS assay was conducted to detect somatic mutations and copy number variations using pre-specified algorithms. Descriptive statistics and hypothesis tests were performed in R. Results: Total 350 blood samples were collected from 160 mBC pts who undertook therapy at Beijing cancer hospital after approved by Research Ethics Committee. Among these pts, the percent of HR+, HER2+ and triple-negative pts is 45%, 27% and 28% respectively. FFPE tissue slides at initial diagnosis were also available for a subset of pts. The most frequent muta...