Impact of sensitive circulating tumor DNA monitoring on CT scan intervals during postoperative colorectal cancer surveillance

Objective This study investigated whether digital PCR (dPCR)-based circulating tumor DNA (ctDNA) monitoringcan allow longer intervals between computed tomography (CT) scans during postoperative surveillance of colorectal cancer (CRC). Design 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 (i.e., clinical) surveillance using serum tumor markers and CT. 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 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. Nonetheless, ctDNA monitoring would still have provided a lead time of 339 days for detection of clinical relapse (range, 42-533 days). Conclusion Our findings suggest that the ctDNA monitoring as part of post-operative surveillance and clinical relapse detection for patients with CRC could allow the CT interval to be lengthened.