Detection of actionable gene mutations in breast cancer by amplicon-based next-generation sequencing liquid biopsy.

Abstract

1035 Background: The PI3K-inhibitor, alpelisib, was approved for the treatment of hormone receptor (HR)-positive, HER2-negative breast cancers with PIK3CA mutations based on findings from the SOLAR-1 trial. PIK3CA-positivity in tumor tissue was 29% (341/1172), but was only 15% (177/1172) in plasma cell-free DNA (cfDNA). The lower mutation detection rate observed in cfDNA may limit the clinical application of liquid biopsy in breast cancer. Amplicon-based next-generation sequencing (NGS) approach may confer improved sensitivity, allowing more effective profiling. We conducted a study to evaluate the use of this technology. Methods: Plasma cfDNA from 113 breast cancer patients (82.3% metastatic) underwent real-world testing in a CAP and ISO15189 accredited central laboratory. We analysed genetic alterations in cfDNA using an amplicon-based NGS technology. The presence of PIK3CA and other mutations relevant to breast cancer were correlated to molecular subtypes and treatment histories. Results: At least one mutation was detected in 70.8% of cases. Mutations were more frequent in metastatic cases (77.4%) compared to non-metastatic cases (27.3%). Across all patients, mutations in PIK3CA (33.6%), TP53 (32.7%), ESR1 (22.1%), GATA3 (7.1%) and ERBB2 (7.1%) were most frequently detected, in accordance with tumor tissue genotyping studies. PIK3CA mutations were more common in HR+ HER2- patients (44.4% vs 28.6% of other patients). Among PIK3CA-mutant cases, multiple PIK3CA mutations were present in 18.4% of cases, and hotspot mutations H1047R (34.2%), E542K (26.3%) and E545K (15.8%) were most frequent. An association was seen between PIK3CA mutation and prior treatment with CDK4/6 inhibitors (palbociclib, ribociclib) or mTOR inhibitor (everolimus), with 58% of PIK3CA-mutant cases having received these treatment previously compared to only 20% of PIK3CA-wild type (wt) cases. In addition, 75% of previously treated ESR1-mutant cases had specifically received hormonal treatment, compared to 60 % of ESR1-wt cases that received any treatment. Conclusions: We report similar PIK3CA mutation frequencies (~30%) with amplicon-based NGS on cfDNA compared to tumor tissue testing in breast cancer. Importantly, other driver mutations were also observed at similar frequencies as external tissue studies, implying high sensitivity as the primary reason for performance. This supports the clinical utility of an amplicon-based NGS-based approach to liquid biopsy for the sensitive detection of actionable mutations in breast cancer.