Clinical implications of monitoring circulating tumor DNA in patients with colorectal cancer

Purpose: We investigated if detection of circulating tumor DNA (ctDNA) after resection of colorectal cancer (CRC) identifies the patients with the highest risk of relapse, and furthermore, whether longitudinal ctDNA analysis allows early detection of relapse and informs about response to intervention.<br /><br />Experimental Design: In this longitudinal cohort study we used massively parallel sequencing to identify somatic mutations and used these as ctDNA markers to detect minimal residual disease and to monitor changes in tumor burden during a three year follow-up period.<br /><br />Results: A total of 45 patients and 371 plasma samples were included. Longitudinal samples from 27 patients revealed ctDNA post-operatively in all relapsing patients (n=14), but not in any of the non-relapsing patients. ctDNA detected relapse with an average lead-time of 9.4 months compared to CT imaging. Of 21 patients treated for localized disease, six had ctDNA detected within 3 months post-surgery. All six later relapsed compared to four of the remaining patients (Hazard ratio (HR), 37.7, 95% confidence interval (CI), 4.2-335.5; P<0.001). The ability of a 3 month ctDNA analysis to predict relapse was confirmed in 23 liver metastasis patients (HR 4.9; 95%CI, 1.5-15.7; P=0.007). Changes in ctDNA levels induced by relapse intervention (n=19) showed good agreement with changes in tumor volume (Kappa=0.41, Spearman's rho=0.4).<br /><br />Conclusions: Postoperative ctDNA detection provides evidence of residual disease and identifies patients at very high risk of relapse. Longitudinal surveillance enables early detection of relapse and informs about response to intervention. These observations have implications for the post-operative management of CRC patients.

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