Impact of Sensitive Circulating Tumor DNA Monitoring on CT Scan Intervals During Postoperative Colorectal Cancer Surveillance.

Objective: This study investigated whether digital polymerase chain reaction (dPCR)-based circulating tumor DNA (ctDNA) monitoring can allow longer intervals between computed tomography (CT) scans during postoperative surveillance of colorectal cancer (CRC).

Background: Practical guidelines still recommend intensive postoperative surveillance of CRC using periodical CT scans and serum carcinoembryonic antigen testing.

Methods: The longitudinal dynamics of ctDNA for 52 patients with CRC as measured by dPCR using probes targeting 87 individual tumor-specific mutations (1-5 per patient) were compared with results from conventional (ie, clinical) surveillance using serum tumor markers and CT.

Results: A total of 382 CT procedures were carried out for the patient cohort (3.3/year per patient) and the median lead time from ctDNA relapse to clinical relapse was 182 days (range, 0-376 days). If the CT interval was annual, potential delays in the detection of clinical relapse would have occurred for 7 of the 10 patients who experienced clinical relapse (9 of 13 events), with a median delay of 164 days (range, 0-267 days). If annual CT surveillance was performed together with ctDNA monitoring, 218 (57.1%) CTs would not have been needed to detect the first clinical relapse. In addition, the ctDNA monitoring would have provided a lead time of 339 days for detection of clinical relapse (range, 42-533 days).

Conclusions: Our findings suggest that the ctDNA monitoring as part of postoperative surveillance and clinical relapse detection for patients with CRC could allow the CT interval to be lengthened.

Trial registration: This trial was registered with University Hospital Medical Information Network Clinical Trial Registry (UMIN000045114).