Mutational burden on circulating cell-free tumor-DNA testing as a surrogate marker of mismatch repair deficiency or microsatellite instability in patients with colorectal cancers

Circulating cell-free tumor-DNA (cfDNA) testing (‘liquid biopsy’) is increasingly being employed both in clinical trials as well as clinical practice. With respect to colon cancer, the trends in cfDNA are associated with the responses observed (1). Furthermore, it is not only helpful in identifying inherent mutations conferring resistance to targeted therapies e.g., RAS/RAF mutations, it is also useful in identifying acquired mechanisms of resistance e.g., MET-amplifications as a mechanism of resistance to anti-epidermal growth factor receptor (anti-EGFR) monoclonal antibodies (2,3).