Genomic landscape of de novo stage IV breast cancer

1022 Background: Genomic profiling of primary and recurrent metastatic breast cancer (rMBC) has revealed potential resistance mechanisms to therapy. In contrast, de novo stage IV breast cancer (DNIV) represents an opportunity to elucidate metastatic drivers in the absence of treatment selection. Methods: Targeted NGS (Oncopanel, OP) using multiplexed copy number variation (CNV) and mutation (mut) detection across the full coding regions of 300 genes and selected intronic regions of 35 genes was performed on either primary or metastatic samples collected in patients (pts) with DNIV or rMBC. Mut/CNV in primary and metastatic tumors were compared per subtype between DNIV and rMBC using Fisher´s exact test (significant p