Concordance of genomic alterations (GA) in synchronous tumor biopsies (tBx) and circulating tumor (ct) DNA from metastatic breast cancer (MBC) patients (pts).

1073Background: Next generation sequencing (NGS) of tBx is the basis for precision medicine. Most tBx used for NGS are archival primary tumors, often acquired several years before starting matched treatment. Analysis of ctDNA may better capture the GA landscape of MBC. We aimed to compare the concordance of GA detection by NGS in synchronously acquired tBx and ctDNA in MBC pts. Methods: MiSeq Amplicon-based NGS (panel of 59 cancer-related genes) was performed in both tBx and ctDNA at disease progression. The concordance of GA in tBx vs ctDNA was determined at patient level and at mutation (mut) level in clinically actionable genes (PIK3CA, AKT1, ERBB2, ESR1, PTEN). False negative result in ctDNA (FN-ctDNA) defined as mut detected in tBx but not in ctDNA. Results: 28 pts identified (luminal [lum] 21, HER2+ 5, triple negative 2), median prior lines of therapy 4.5 (0-15). Most pts had visceral metastasis (71%); most biopsies were from non-visceral sites (67%), mainly breast/nodes/skin (59%). In 16 pts (57%),...