Digital PCR  and next-generation sequencing (NGS) are becoming the technologies of choice for detecting cancer variants. However, the high sequencing error rate of current NGS platforms is a major problem. In addition, sequencing multiple sites or genomic regions dramatically increases the number of false positives. The introduction of molecular barcodes [3–7] is likely to solve this problem. So called “barcoding” involves the labeling of DNA fragments with unique oligonucleotides, typically 10–15 bases long, which enables reads from the same DNA fragment to be grouped together. Constructing a consensus read from the grouped reads eliminates sequencing errors as well as errors introduced during PCR. However, molecular barcodes cannot detect base substitutions in genomic DNA introduced by DNA damage, and somatic mutations that preexist at a low frequency in the cells of healthy individuals  also make it difficult to discriminate ctDNA from cfDNA originating from normal cells. Thus, to use NGS for diagnostic purposes, such variants must be removed.