To this aim, the concentration of tumour ctDNA in plasma samples of mice xenografted with SW620 cells was quantified using three human KRAS primer pairs that amplify sequences of 73 bp, 145 bp and 300 bp (Fig. 2, B) and with KRAS primers targeting mouse and human KRAS (214 and 189 bp, Figure S1). This evidence concerns the gene KRAS and neoplasm.