Monitoring of gastrointestinal carcinoma via molecular residual disease with circulating tumor DNA using a tumor‐informed assay

BACKGROUND: Circulating tumor DNA (ctDNA)‐based minimal residual disease (MRD) detection, which can identify disease relapse ahead of radiological imaging, has shown promising performance. The objective of this study was to develop and validate OriMIRACLE S (Minimal Residual Circulating Nucleic Acid Longitudinal Detection in Solid Tumor), a highly sensitive and specific tumor‐informed assay for MRD detection. METHODS: Tumor‐specific somatic single nucleotide variants (SNVs) were identified via whole exome sequencing of tumor tissue and matched germline DNA. Clonal SNVs were selected using the OriSelector algorithm for patient‐specific, multiplex PCR‐based NGS assays in MRD detection. Plasma‐free DNA from patients with gastrointestinal tumors prior to and following an operation, and during monitoring, were ultradeep sequenced. RESULTS: The detection of three positive sites was sufficient to achieve nearly 100% overall sample level sensitivity and specificity and was determined by calculating binomial probability based on customized panels containing 21 to 30 variants. A total of 127 patients with gastrointestinal tumors were enrolled in our study. Preoperatively, MRD was positive in 18 of 26 patients (69.23%). Following surgery, MRD was positive in 24 of 82 patients (29.27%). The positivity rate for MRD was 33.33% (n = 18) for gastric adenocarcinoma and 32.26% (n = 62) for colorectal cancer. Twenty (20) of 59 patients (34.48%) experienced a change in MRD status over the monitoring period. Patients 8 and 31 responded to 3 cycles of systemic therapy, after which levels for all ctDNA dropped below the detection limit. Patient 53 was an example of using MRD to predict tumor metastasis. Patient 55 showed a weak response to treatments first and respond to new systemic therapy after tumor progression. CONCLUSION: Our study identified a sensitive and specific clinical detection method for low frequency ctDNA, and explored the detection performance of this technology in gastrointestinal tumors.