134P Unmasking actionable mutations in HR+/HER2–metastatic breast cancer: Real-world insights from Avida DNA OncoLiquid BiopsyNGS combined with methylation index

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Background: In HR+/HER2-metastatic breast cancer (MBC), ESR1 and/or PI3K pathway (PIK3CA, AKT1 and PTEN) mutations guide post-first-line therapeutic strategies.We report data on mutation prevalence in MBCs patients (pts) assessed via Avida Duo Liquid Biopsy (LB)-NGS based (Agilent Technologies) at ASST PGXXIII, Bergamo (IT).Methods: Between October 2023 and May 2025, 41 HR+/HER2-endocrine-treated MBC pts, were tested externally using the Oncomine™ Breast cfDNA Assay v2 (ThermoFisher).Since May 2025, our lab implemented the NGS assay with Avida Duo a dual-omics LB platform that provides both DNA variants and methylation index (MI) from a single input.We analyzed ctDNA from 9/41 pts, to validate our AVIDA DNA OncoLB data.Matched tissue samples (n=5) were tested with the same panel to confirm the detected mutations.Results: All 9 samples were successfully analyzed in our lab.Targetable mutations were identified in 5/9 pts (55%) via our LB assay-PIK3CA (33%), AKT1 (22%), and PTEN (22%)including mutations missed externally.The Avida DNA test rescued 2 cases labeled 'unanalyzable' externally, detecting key mutations (PIK3CA, AKT1, and TP53).Conversely, in 2 cases mutations identified by the external lab were detected alongside additional PTEN mutations, which are not included in the ThermoFisher panel.Concordance with tissues was observed in 4/5 cases (Tab.1);discordance was associated with low variant allele frequency.MI confimed tumor-derived ctDNA is all 8 evaluable cases, validating LB findings.

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