A noninvasive gastric cancer Her2 test using surrogate methylation markers.

Abstract

e16084 Background: There are 10-20% of gastric cancer (GC) with overexpressed Her2. Her2 status remains an essential biomarker for guiding the trastuzumab (Herceptin) therapy, a monoclonal antibody approved for the first-line treatment of late-stage Her2-positive GC. Although IHC, together with FISH, is comprehensively applied to verify Her2 status on tissue samples, an accurate blood test is highly desirable due to the inaccessibility of tissue samples, especially in very late stage GC patients as well as tumor heterogeneity of tissue biopsy. Detecting copy number aberration of Her2 gene in cell-free DNA (cfDNA) gains a lot of interest for its non-invasive approach. However, the limited signal-to-noise ratio poses a great challenge for the accuracy and robustness of the tests (either targeted sequencing or ddPCR). Here, we report a non-invasive test for Her2 status verification based on novel surrogate DNA methylation markers. Methods: Genome-wide DNA methylation sequencing was performed in 30 Her2-negative (IHC 0/1+) and 44 Her2-positive (IHC 3+) tissue samples to identify Her2-overexpression-specific methylation markers. Then we analyzed the performance of these candidate markers using methylation-specific quantitative PCR (qMSP) in plasma samples collected from 102 GC patients before surgical treatment. A Her2-status diagnostic model was built and further validated in a multi-center, prospective cohort (n = 150). The concordance of Her2 status between GC plasma and matching tissue samples (IHC/FISH) was determined. Results: We first discovered 102 statistically significant methylation markers of Her2 status in tissue. Out of these candidate markers, a 3-marker diagnostic model was built and validated on plasma samples, which could discriminate Her2-positive from Her2-negative GC patients with high sensitivity (86.7%) and specificity (96.8%). The overall plasma-tissue concordance of this liquid biopsy test was 95.3%. Furthermore, the Her2-status test was able to classify Her2 2+ status (IHC) into either Her2-negative or Her2-positive status, which was confirmed by conventional FISH test. Conclusions: Overall, the cfDNA-based test is a novel, accurate and noninvasive approach for determining Her2 status in GC patients. The high concordance with IHC/FISH results of this blood test holds great promise as an auxiliary method for guiding Her2-targeted therapy in GC patients. A clinical trial is undergoing to validate this test in the phase-2 clinical trial of a Her2-targeted drug (for GC) in China.