Circulating tumor DNA as a marker of minimal residual disease following local treatment of metastases from colorectal cancer.

Background: Local treatment of liver and/or lung metastases from colorectal cancer (CRC) is increasingly used in daily practice and comprises resection, radiofrequency ablation (RFA) and stereotactic radiotherapy (SBRT). The need for prognostic markers for patients undergoing such treatment is currently unmet. We investigated post-treatment circulating tumor-specific DNA (ctDNA) analysis and address a possible prognostic value in a pilot study.
Materials: From July 2015 to September 2017, patients undergoing standard of care local treatment of liver and/or lung metastases were included in a prospective translational study. Blood samples were drawn 2 weeks after local treatment and during follow-up. CtDNA was detected by ddPCR and a mass spectrometry-based platform MassARRAY ^® .
Results: Post treatment blood samples were available for 35 patients including five with detectable ctDNA (KRAS mutation, n  = 2; NRAS mutation, n  = 2; BRAF mutation, n  = 1) by ddPCR. 17 out of 35 patients (49%) developed recurrence within a median of 273 days (95%CI 95-NA) among patients positive for ctDNA, while the median time to recurrence was not reached for the group of patients negative for ctDNA ( p  = .03).
Conclusion: The presence of ctDNA following local treatment of metastatic CRC is associated with an increased risk of recurrence and a short time to failure.