Detection And Description Of Erbb2 Amplification Using Circulating Cell Free Tumor Dna (Ctdna) Genomic Analysis In Metastatic Colorectal Cancer (Mcrc).

661Background: ERBB2 amplification (HER2amp) is evolving as a distinct subset of mCRC with therapeutic implications. Although seen in 3-4% of mCRC in tumor tissue, little is known about occurrence of HER2amp in ctDNA. The purpose of this study was to assess the value of ctDNA in detection of HER2amp in blood and to delineate its landscape in mCRC. Methods: We performed a retrospective analysis of mCRC patients (pts) who underwent plasma-derived NGS of ctDNA in a CLIA-certified lab (Guardant Health, Inc.) using a high sensitivity assay that reports copy-number variations using pre-specified algorithms. Pts with no detectable alterations were excluded. The cohort was divided into 2 groups: HER2amp and ERBB2 non-amplified (HER2NA). Descriptive statistics and Fisher’s exact test were used. Results: Between 5/2014 and 5/2016, 1625 mCRC pts had a ctDNA NGS assay and of these 1387 met our inclusion criteria. Among these, HER2amp was seen in 69 pts (4.9%, 95%CI: 3.9 – 6.3). HER2amp were found to be enriched in RA...