Abstract 5684: NSABP FC-7 correlative study: HER2 amplification (amp) in circulating cell-free DNA (cfDNA) in metastatic colorectal cancer (mCRC) resistant to anti-EGFR therapy (tx)
Authors: Kim S. Rim , Srinivasan Ashok , Allegra Carmen J. , Jacobs Samuel , Nagy Rebecca J. , Lanman Richard B. , Talasaz AmirAli , Gavin Patrick , Pal Rekha , Lucas Peter C. , Pogue-Geile Kay 
Published: July 2017

Background: FC-7 is a phase Ib study hypothesizing that dual ERBB blockade (neratinib and cetuximab) could overcome an acquired resistance mechanism to anti-EGFR tx in KRAS/NRAS/BRAF/PI3KCA wild type (wt) mCRC patients (pts). Previously we demonstrated a 36% rate of HER2 amp in post- anti-EGFR biopsies (bxs). Assay of plasma cfDNA is minimally invasive and may provide comprehensive genomic profiling. We tested the accuracy of a cfDNA assay for HER2 amp, comparing results from matched bxs to evaluate molecular changes in HER2 copy number. Methods: 23 pts with mCRC resistant to anti-EGFR tx were enrolled and treated with cetuximab and neratinib. 17 paired bxs (6 post-tx bxs had insufficient tumor) were assessed for HER2 amp using chromogenic in situ hybridization (CISH) (Dako PharmDxTM). HER2 was considered amplified when HER2/CEP17 ratio was ≥2. cfDNA was extracted from plasma of 11 pts after 1st line anti-EGFR tx but before addition of cetuximab and neratinib. 5-30 ng of DNA was sequenced across 512 exons in 54 genes with HiSeq (Illumina). Copy number variants (CNV) were quantified using a customized pipeline (Guardant 360). One plasma sample failed to yield sufficient cfDNA. 10 pts had comparison of cfDNA with pre- or post- anti-EGFR bx. Results: 4 of 9 plasma samples (1 non evaluable) had HER2 amp, all concordant with pre- or post- anti-EGFR tx tissue. 3 pts converted to HER2 amp after anti-EGFR tx (pts 3, 5, 7), and for 2 of these conversions (pts 5, 7), the amplification was evident in cfDNA.

PtPre- anti-EGFR CISH RatioPost- anti-EGFR CISH RatioPost- anti-EGFR cfDNA CNVConcordance of cfDNA with pre- or post-anti-EGFR Tissue Samples1Neg (1.0)Neg (1.3)Non evaluableNA2Pos (2.5)Neg (1.5)Pos (2.66)Pre-Tx3Neg (1.0)Pos (3.7)NegPre-Tx4Neg (1.0)Neg (1.8)NegBoth5Neg (1.2)Pos (2.7)Pos (2.48)Post-Tx6Pos (&gt;10)QNSPos (21.86)Pre-Tx7Neg (1.1)Pos (2.0)Pos (2.20)Post-Tx8Neg (1.3)Neg (1.1)NegBoth9Neg (1.0)Neg (1.3)NegBoth10Neg (1.0)Neg (1.5)NegBoth

Conclusion: In this sample set, HER2 amp detected in plasma-derived cfDNA from mCRC pts resistant to anti-EGFR tx is comparable to amp assessed in primary or metastatic tissue. Given advantages of liquid bx relative to repeated tissue bxs, measurement of HER2 amp in cfDNA may be of utility in monitoring pts for resistance to anti-EGFR tx. This will need to be confirmed in a trial incorporating both plasma and tissue samples. Support: Puma Biotechnology, Inc.

Citation Format: S. Rim Kim, Ashok Srinivasan, Carmen J. Allegra, Samuel Jacobs, Rebecca J. Nagy, Richard B. Lanman, AmirAli Talasaz, Patrick Gavin, Rekha Pal, Peter C. Lucas, Kay Pogue-Geile. NSABP FC-7 correlative study: HER2 amplification (amp) in circulating cell-free DNA (cfDNA) in metastatic colorectal cancer (mCRC) resistant to anti-EGFR therapy (tx) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5684. doi:10.1158/1538-7445.AM2017-5684