Unraveling the potential clinical utility of circulating tumor DNA detection in colorectal cancer—evaluation in a nationwide Danish cohort

BackgroundIncreasingly, circulating tumor DNA (ctDNA) is proposed as a tool for minimal residual disease (MRD) assessment. Digital PCR (dPCR) offers low analysis costs and turnaround times of less than a day, making it ripe for clinical implementation. Here, we used tumor-informed dPCR for ctDNA detection in a large CRC cohort to evaluate the potential for postoperative risk assessment and serial monitoring, and how the metastatic site may impact ctDNA detection. Additionally, we assessed how altering the ctDNA calling algorithm could customize performance for different clinical settings.Patients and methodsStage II-III CRC patients (N=851) treated with curative intent were recruited. Based on whole exome sequencing on matched tumor and germline DNA, a mutational target was selected for dPCR analysis. Plasma samples (8mL) were collected within 60 days post operation and – for a patient subset (n=246) – every 3-4 months for up to 36 months. Single-target dPCR was used for ctDNA detection.ResultsBoth postoperative and serial ctDNA detection was prognostic of recurrence (HR=11.3, 95%CI 7.8-16.4, P<0.001; HR=30.7, 95%CI 20.2-46.7, P<0.001), with a cumulative ctDNA detection rate of 87% at the end of sample collection in recurrence patients. The ctDNA growth rate was prognostic of survival (HR=2.6, 95%CI 1.5-4.4, P=0.001). In recurrence patients, postoperative ctDNA detection was challenging for lung metastases (4/21 detected) and peritoneal metastases (2/10 detected). By modifying the cutoff for calling a sample ctDNA positive, we were able to adjust the sensitivity and specificity of our test for different clinical contexts.ConclusionsThe presented results from 851 stage II-III CRC patients demonstrate that our personalized dPCR approach effectively detects MRD post operation and shows promise for serial ctDNA detection for recurrence surveillance. The ability to adjust sensitivity and specificity shows exciting potential to customize the ctDNA caller for specific clinical settings.