Use of tumor-informed ctDNA across gastrointestinal cancers.

Abstract

758 Background: In colorectal cancer (CRC), the use of ctDNA for the purpose of early recurrence detection and prognostication is established, and multiple studies are testing its utility for guiding adjuvant therapy decisions. Tumor informed testing can be performed in clinical situations where adequate tissue is available for next-generation sequencing (NGS). Increasingly, ctDNA testing is being used clinically for colorectal cancer patients and other gastrointestinal (GI) cancers when there is an appropriate clinical scenario and adequate tumor tissue is available for sequencing. Methods: We identified GI cancer patients treated at our institution where Signatera (Natera) testing was ordered and performed between 2020 – 2023. We included all patients for whom testing was ordered. Then, among patients with any result further analyzed results by disease type, stage, and results. We examined clinical rationale for testing and whether results informed subsequent decisions. Results: A total of 99 GI cancer patients for whom ctDNA testing was ordered were identified. 80 patients had at least 1 ctDNA result including 68 colorectal patients and 12 other GI cancers (anal, bile duct, esophagogastric, pancreatic, and small bowel). Among patients with measurable ctDNA, at the most recent testing timepoint 16 had levels that met criteria for positive detection, while 64 were undetectable. Most commonly, testing was ordered in stage II/III CRC patients for post-operative surveillance. Other clinical use scenarios included 1) surveillance/treatment monitoring in oligometastatic CRC, 2) surveillance in non-metastatic esophagogastric cancer, 3) treatment monitoring in MSI-H/immunotherapy sensitive GI cancers. For at least 18 patients, results were a factor in shared clinical decision making between patients and providers. Conclusions: We found ctDNA monitoring is most commonly used in the adjuvant setting for CRC patients which is best supported by existing studies. Our data demonstrates that tumor informed testing can be successful in other GI cancers for both surveillance and therapy monitoring. Given the broad and rapid adoption of this technology, there needs to be continued efforts for both prospective validation studies and retrospective real world studies to guide clinical practice.