Clinical validation of Northstar response: A novel methylated ctDNA therapy response monitoring assay in patients with advanced gastrointestinal cancers.

Abstract

e16000 Background: Circulating tumor DNA (ctDNA) offers a non-invasive method to comprehensively assess tumors. While most assays for therapy response monitoring rely on variant allele frequencies, methylated ctDNA has shown promise. However, accuracy has been limited by quantification precision. The CLIA-approved Northstar Response assay quantifies over 550 hyper-methylated loci and has demonstrated a 10-fold increase in detection signal over tissue-informed assays. Methods: We present an interim analysis from an ongoing prospective, observational study designed to assess the clinical validity of Northstar Response as a tool to monitor therapeutic response without prior tumor tissue. Our study aims to include 100 advanced GI cancer patients undergoing systemic therapies for advanced disease. Serial ctDNA measurements are collected at baseline, approximately every 30 days post-treatment initiation, and with imaging assessments. The primary endpoint is concordance between ctDNA and RECISTv1.1 criteria for disease response until progression or death. Results: Baseline ctDNA characteristics were examined from 44 patients, with 23 undergoing at least two longitudinal blood collections and subsequent imaging. The median age in this cohort was 65.5 years, with a male predominance (70.5%) and a majority identifying as White (79.5%). Cancers included esophageal (18.2%), hepatocellular (29.5%), biliary (15.9%) and colorectal (15.9%), among others. A majority (59.1%) had both primary and metastatic lesions. Baseline methylation scores ranged from 280 in biliary cancers to 100,000 in colorectal cancers. Those on second-line treatments had lower scores than first or third-line therapies. Methylation scores decreased in patients responding to treatment, indicating that these scores have the potential to serve as indicators of therapeutic efficacy. Conclusions: Baseline methylation scores differ across GI tumor types, disease burdens, and treatment lines, reflecting the complexity of using methylation as a biomarker. Northstar Response has shown initial promise in monitoring therapy response in GI cancers. More mature data, which will further elucidate the assay's clinical utility, will be presented at the meeting.