ctDNA can be explored by different ways: a quantitative approach in which ctDNA concentration is measured; a targeted sequencing approach (mostly by digital droplet PCR, ddPCR), to determine specific mutation profile as epidermal growth factor receptor (EGFR) mutations for example, or large ctDNA sequencing (next-generation sequencing, whole-exome sequencing) to have an extended view on mutational tumor profile and evaluate the mutational burden, also defined as blood tumor mutational burden (bTMB). This evidence concerns the gene EGFR and neoplasm.