The withdrawal of anti-EGFR therapy correlates with a decline in KRAS-mutant allelic fraction in ctDNA obtained from patients with metastatic CRC with resistance to anti-EGFR therapies owing to an acquired KRAS mutation, suggesting that ctDNA analysis might enable real-time monitoring of the effects of the selective pressures of targeted therapies on tumour populations101. This evidence concerns the gene KRAS and colorectal carcinoma.