Abstract 506: Post-surgical resection monitoring in early stage colorectal carcinoma patients using a circulating cell-free DNA assay with ultra-high accuracy and specificity
Authors: Mortimer Stefanie A. , Dilger Katharine , Fairclough Stephen , Abdueva Diana , Chudova Darya , Sarin Ankit , Leng Jim , Lee Jeeyun , Eltoukhy Helmy , Talasaz AmirAli 
Published: July 2016

Abstract
Analysis of cell-free circulating tumor DNA (ctDNA) by next-generation sequencing (NGS) allows non-invasive real-time profiling of actionable genomic alterations. Liquid biopsy provides an option for disease monitoring in early stage cancer patients post surgical resection, with a potential to aid in adjuvant decision making. However, to be applicable, tests must cover a broad enough genomic footprint to not require a priori knowledge of mutations, have high specificity, and sensitivity higher than conventional methods. NGS is necessary, since inactivating mutations are the most common alteration type in many common cancer types such as colorectal carcinomas (CRC).
Here we present a highly efficient and specific NGS assay for detection of ctDNA in early stage cancer patients, capable of detecting single molecule variants across a 12 kb gene panel with an analytical sensitivity of &gt;0.02% for single nucleotide variants (SNVs) and indels. This panel was applied to a clinical study involving 14 early stage (II/III) CRC patients with both pre- and post-op blood draws (up to 7 days post surgery). A subset (6 patients) also had tumor samples collected at the time of the surgical resection of the tumor.
Overall, the detection rate of ctDNA in pre-op blood draws was 93%. In the post-op blood draws ctDNA was detectable in 43% of cases. The estimated average minor allele frequency (MAF) is 0.58% (± 0.82%) in pre-op, 0.18% (±0.21%) in post-op, and 40% (±18%) in tumor samples. When tumor tissue was available and used as a reference, the clinical sensitivity, specificity, and accuracy in pre-op blood samples were 83%, 99.995%, and 99.99%, respectively. SNVs with MAF as low as 0.04% were confirmed in tissue data. The clinical specificity of variants detected in post-op blood samples using pre-op samples as the reference is 99.996%. Cohort expansion to 50 patients and follow-up for clinical recurrence in both cohorts is ongoing.
In conclusion, we have developed an assay with ultra-high accuracy and specificity, for the detection of ctDNA in early stage CRC patients that is capable of detecting alterations present in the tumor post-surgical resection. This technology allows for a promising non-invasive route for molecular monitoring of residual disease post surgery and for early detection of relapse compared to traditional methodologies.
Citation Format: Stefanie A. Mortimer, Katharine Dilger, Stephen Fairclough, Diana Abdueva, Darya Chudova, Ankit Sarin, Jim Leng, Jeeyun Lee, Helmy Eltoukhy, AmirAli Talasaz. Post-surgical resection monitoring in early stage colorectal carcinoma patients using a circulating cell-free DNA assay with ultra-high accuracy and specificity. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 506.