Abstract 4918: Concordance of circulating tumor DNA (ctDNA) and next-generation sequencing (NGS) as molecular monitoring tools in metastatic breast cancer (MBC)
Authors: Austin Laura K. , Avery Tiffany , Jaslow Rebecca , Fortina Paolo , Sebisanovic Dragan , Siew LaiMun , Zapanta Aubrey , Talasaz AmirAli , Cristofanilli Massimo 
Published: August 2015

Abstract
Background
MBC is an incurable disease with complex molecular features including somatic mutations that evolve in relation to genomic instability and selective treatment pressure. Patients with treatment-refractory MBC may benefit from tissue genomic evaluation using next-genomic sequencing (NGS). Furthermore, circulating DNA fragments with tumor-specific sequence alterations (ctDNA) found in the blood of patients with advanced disease offer the possibility of non-invasive molecular monitoring. ctDNA detects actionable mutations with the advantage of serial evaluation and allowing capture of inter- and intra-tumor heterogeneity.
Methods
This is a retrospective evaluation of 28 patients with MBC who failed standard therapies and had baseline plasma analyzed for ctDNA and tissue analysis (NGS) before starting new therapy. We were interested in the performance of the ctDNA test and the concordance rate of genomic alterations detected in the two tests. Selection criteria: progression of disease after standard therapies, need to detect novel molecular abnormalities for possible therapeutic targeting, or confirmation of persistence of genomic abnormalities already demonstrated in tissue or blood analysis. Guardant360™(Guardant Health) involves comprehensive sequencing of a panel of 54 gene associated with solid tumors using single-molecule digital sequencing technology. FoundationOne®(Foundation Medicine) performed the NGS on tissue evaluates the entire coding sequence of 315 cancer-related genes.
Results
All patients had biopsy-proved metastatic disease, and had ctDNA and NGS performed. 93% of patients had ctDNA alterations detected (with 0.1%-27.8% circulating tumor fraction), and 9 patients had serial ctDNA. Overall, for the patients we detected mutations in ctDNA and tissue, 89% of patients had a specific alteration on ctDNA that matched the NGS analysis. Among all mutations detected in tumors which are in overlapped genes, 71% of alterations were common (83% excluding gene amplifications). Interestingly, for patients who had both tests done within 8 weeks, 70% of had additional alterations in the ctDNA that were not found on NGS, such as ERBB2 mutations.
Conclusions
Genomic analysis using ctDNA and NGS detects genomic abnormalities in all patients with MBC with high concordance. However, each method was able to detect alterations that the other did not, suggesting the two methods can be complementary in detecting actionable mutations and expanding therapeutic options. Intriguingly, this occurred more frequently with the ctDNA, demonstrating its utility as an adjunct to tissue sampling which permits capture of the inter- and intra-tumor heterogeneity of the disease, and warrants further investigation prospectively.
Citation Format: Laura K. Austin, Tiffany Avery, Rebecca Jaslow, Paolo Fortina, Dragan Sebisanovic, LaiMun Siew, Aubrey Zapanta, AmirAli Talasaz, Massimo Cristofanilli. Concordance of circulating tumor DNA (ctDNA) and next-generation sequencing (NGS) as molecular monitoring tools in metastatic breast cancer (MBC). [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4918. doi:10.1158/1538-7445.AM2015-4918